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Agradecimentos: D.U. acknowledges financial support from the Brazilian Agencies FAPESP (No. 2014/01045-0), CNPq (402571/2016-9 and No. 306513/2017-0) and FAEPEX-UNICAMP. V.R. thanks funding from FAPESP (2007/01722-9) and CNPq (555647/2006-4 and 577046/2008-0). M.M. thanks funding from CNPq (No. 162541/2018-0). Access to the FEG-TEM/STEM from the Brazilian Nanotechnology National Laboratory is acknowledged (LNNANO, grant No. ME - 22329). M.A.C. acknowledges financial support from FAPESP (Nos. 2013/02300-1 and 2013/10957-0) and CNPq (No. 479486/ 2012-3). L.H.G.T., G.D., and C.D. acknowledge funding from the European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 312483 (ESTEEM2). M.H. acknowledges financial support from FAPESP (No. 2016/12807-4) Abstract: Scanning transmission electron microscopy is a crucial tool for nanoscience, achieving sub-nanometric spatial resolution in both image and spectroscopic studies. This generates large datasets that cannot be analyzed without computational assistance. The so-called machine learning procedures can exploit redundancies and find hidden correlations. Principal component analysis (PCA) is the most popular approach to denoise data by reducing data dimensionality and extracting meaningful information; however, there are many open questions on the accuracy of reconstructions. We have used experiments and simulations to analyze the effect of PCA on quantitative chemical analysis of binary alloy (AuAg) nanoparticles using energy-dispersive X-ray spectroscopy. Our results demonstrate that it is possible to obtain very good fidelity of chemical composition distribution when the signal-to-noise ratio exceeds a certain minimal level. Accurate denoising derives from a complex interplay between redundancy (data matrix size), counting noise, and noiseless data intensity variance (associated with sample chemical composition dispersion). We have suggested several quantitative bias estimators and noise evaluation procedures to help in the analysis and design of experiments. This work demonstrates the high potential of PCA denoising, but it also highlights the limitations and pitfalls that need to be avoided to minimize artifacts and perform reliable quantification FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: The authors would like to thank Dr. Richard Janissen (TU Delft, The Netherlands) for fruitful scientific discussions. The authors are greatly indebted to Vladimir Gaal and Marcos Puydinger (IFGW, UNICAMP) for their technical assistance. This work was financially supported by Samsung Eletrônica da Amazônia Ltda under the Brazilian Informatics Law 8.248/91 and partly by the Brazilian agencies CNPq (441799/2016-7) and FAPESP (grant 2019/07616-3). S.A, A.M.S and U.F.S.R acknowledges FAPESP, CNPq and CAPES, respectively, for funding their scholarships. We thank INFABIC/UNICAMP (FAPESP: 2014/50938-8, CNPq 465699/2014-6) and LAMULT – IFGW/UNICAMP for granting access to their facilities. We also acknowledge access to clean room facilities at both Semiconductor Component Center (CCSNano, UNICAMP) and Device Research Laboratory (IFGW, UNICAMP) Abstract: SU-8 is an attractive platform for the development of smart biochips owing to its high aspect ratio of micro/ nanostructures fabrication and remarkable optical and biocompatible properties. However, few works have explored sub-micron SU-8 thin films for applications in new generations of portable bioanalytical devices. In this work we discuss surface properties for the efficient immobilization of different bioanalytical components on SU-8 thin film surfaces. Short exposure time oxygen plasma treatment improved hydrophilicity and activation of surface carboxyl groups of 300 nm-thick SU-8 films, while maintaining surface roughness below 2 nm. Under these optimized surfaces conditions, covalent immobilization of Interleukin-6 and Prostate Specific Antigen antibodies on SU-8 surfaces was evaluated using quantitative fluorescence microscopy. The addition of standard crosslinker, 1-ethyl-3-(3-(dimethylamino)-propyl)-carbodiimide and N-hydroxysuccinimide mixture to our protocol yielded 15?20% higher antibody immobilization due to activation of surface carboxyl groups. The stability of the plasma treatment along time, and the ideal surface passivation of functionalized samples are demonstrated, along with the selective immobilization antibody to photolithographically-patterned SU-8 microstructures. Overall, our optimized protocol could find broad applications of functionalized SU-8 thin films in biomedical fields, particularly for the fabrication of SU-8 based miniaturized photonic and plasmonic biosensors CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: The authors acknowledge the support from Analytical Resources and Calibration Laboratory (LRAC) from the Chemical Engineering Department and the Multi-User Lab (LAMULT) from Institute of Physics "Gleb Wataghin", both at UNICAMP, which provided invaluable access to their equipment. We would also like to thank the National Nanotechnology Laboratory (LNNano) for granting access to the electron microscopy facilities. This work was financially supported by FAPESP (2019/07616-3, 2017/21235-7, and 2015/16611-4), FAPEMIG (PPM-00431-17) and CNPq (311677/2018-5, 429326/2018-1, 309285/2017-8). J. Hernandez-Montelongo and G. Gonçalves Nicastro acknowledge FAPESP scholarship (2013/14888-3 and 2013/02375-1, respectively). M. Zavarize acknowledges CNPq scholarship (141023/2017-1) Abstract: Materials coated with nanofilms obtained by polyelectrolytes assembled layer-by-layer are promising as antibacterial surfaces. Nanofilms of hyaluronan/chitosan (HA/CHI) have satisfactory antibacterial effects against human pathogenic bacteria, such as Escherichia coli and Staphylococcus aureus, but are not efficient for Pseudomonas aeruginosa. To better understand the interaction between P. aeruginosa and HA/CHI nanofilms, this work evaluates the role of type IV pili (T4P) and lipopolysaccharide (LPS) structures in the initial adhesion of this opportunistic pathogen on a bioinert silica substrate and a 20 nm-thick HA/CHI nanofilm using two genetically modified strains: Delta pilA and LPS-. Delta pilA cannot twitch and LPS- lacks the O-antigen structures of LPS molecules. Our results indicate that each strain presented a different adhesion on both surfaces according to their particular features. For the silica substrate, the PA14 wild-type strain exhibited motility because formed interconnected rings, as a result of cell motility; however, in the case of Delta pilA strain, nonconfluent aggregates were generated by the lack of twitching motility in cells. For the LPS- strain, bacteria completely covered the silica, demonstrating a significantly higher rate of adhesion and growth when compared to the other strains. The HA/CHI nanofilm produced membrane damage and lysis on all the used strains, confirming its antibacterial effect during the first hours of culture. However, the lack of LPS seemed to protect the bacteria partially from the HA/CHI nanofilm, probably due to their autoaggregative phenotype, preventing the exposure of part of the cells to the nanofilm. Moreover, in the case of PA14 wild-type, cells were able to adhere on top of the lysed bacteria, using them as a new surface. This behavior may explain why this antibacterial material has not been so efficient against P. aeruginosa for longer culture times FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIG CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: The authors would like to thank Prof. Steven E. Lindow (University of California, Berkeley) for fruitful discussions. The authors are greatly indebted to Vitor Pelegati (IB, UNICAMP) and Marcos Puydinger (IFGW, UNICAMP) for their technical assistance during confocal microscopy measurements and cleanroom instruments use, respectively. The authors thank INFABIC/UNICAMP (FAPESP: 2014/50938-8, CNPq: 465699/2014-6), LAMULT and Device Research Laboratory (IFGW, UNICAMP) for granting access to their facilities. This work was financially supported by the Brazilian agencies CNPq (441799/2016-7 and 429326/2018-1) and FAPESP (Grants number 2013/10957-0 and 2019/07616-3). S.A. and A.M.S. acknowledge FAPESP (2017/14398-7) and CNPq, respectively, for funding their scholarships Abstract: The morphological plasticity of bacteria to form filamentous cells commonly represents an adaptive strategy induced by stresses. In contrast, for diverse human and plant pathogens, filamentous cells have been recently observed during biofilm formation, but their functions and triggering mechanisms remain unclear. To experimentally identify the underlying function and hypothesized cell communication triggers of such cell morphogenesis, spatially controlled cell patterning is pivotal. Here, we demonstrate highly selective cell adhesion of the biofilm-forming phytopathogen Xylella fastidiosa to gold-patterned SiO2 substrates with well-defined geometries and dimensions. The consequent control of both cell density and distances between cell clusters demonstrated that filamentous cell formation depends on cell cluster density, and their ability to interconnect neighboring cell clusters is distance-dependent. This process allows the creation of large interconnected cell clusters that form the structural framework for macroscale biofilms. The addition of diffusible signaling molecules from supernatant extracts provides evidence that cell filamentation is induced by quorum sensing. These findings and our innovative platform could facilitate therapeutic developments targeting biofilm formation mechanisms of X. fastidiosa and other pathogens FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: This work was supported by the Netherlands Organization for Scientific Research (NWO/OCW) as part of the Frontiers of Nanoscience program (2015SYN08) and the Brazilian funding agencies FAPESP (2010/18107-8, 2010/51748-7, 2012/51580-4, 2013/02300-1, and 2015/16611-4) and CNPq (479486/2012-3 and 429326/2018-1) Abstract: Graphene oxide (GO) has immense potential for widespread use in diverse in vitro and in vivo biomedical applications owing to its thermal and chemical resistance, excellent electrical properties and solubility, and high surface-to-volume ratio. However, development of GO-based biological nanocomposites and biosensors has been hampered by its poor intrinsic biocompatibility and difficult covalent biofunctionalization across its lattice. Many studies exploit the strategy of chemically modifying GO by noncovalent and reversible attachment of (bio)molecules or sole covalent biofunctionalization of residual moieties at the lattice edges, resulting in a low coating coverage and a largely bioincompatible composite. Here, we address these problems and present a facile yet powerful method for the covalent biofunctionalization of GO using colamine (CA) and the poly(ethylene glycol) cross-linker that results in a vast improvement in the biomolecular coating density and heterogeneity across the entire GO lattice. We further demonstrate that our biofunctionalized GO with CA as the cross-linker provides superior nonspecific biomolecule adhesion suppression with increased biomarker detection sensitivity in a DNA-biosensing assay compared to the (3-aminopropyl)triethoxysilane cross-linker. Our optimized biofunctionalization method will aid the development of GO-based in situ applications including biosensors, tissue nanocomposites, and drug carriers FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: This work was supported by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil), grants 2010/51748-7, 2013/10957-0, and 2015/16611-4 and Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brazil), grant numbers 479486/2012-3 and 441799/2016-7. M.P.M. acknowledges scholarship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Brazil). J.H.-M and P.K.S. acknowledge FAPESP for funding their scholarships. This work also benefited from equipment access granted by Laboratory of Microfabrication at the National Nanotechnology Laboratory at Centro Nacional de Pesquisa em Energia e Materiais, Brazil Abstract: Microchannels can be used to simulate xylem vessels and investigate phytopathogen colonization under controlled conditions. In this work, we explore surface functionalization strategies for polydimethylsiloxane and glass microchannels to study microenvironment colonization by Xylella fastidiosa subsp. pauca cells. We closely monitored cell initial adhesion, growth, and motility inside microfluidic channels as a function of chemical environments that mimic those found in xylem vessels. Carboxymethylcellulose (CMC), a synthetic cellulose, and an adhesin that is overexpressed during early stages of X. fastidiosa biofilm formation, XadA1 protein, were immobilized on the device’s internal surfaces. This latter protocol increased bacterial density as compared with CMC. We quantitatively evaluated the different X. fastidiosa attachment affinities to each type of microchannel surface using a mathematical model and experimental observations acquired under constant flow of culture medium. We thus estimate that bacterial cells present ~4 and 82% better adhesion rates in CMC- and XadA1-functionalized channels, respectively. Furthermore, variable flow experiments show that bacterial adhesion forces against shear stresses approximately doubled in value for the XadA1-functionalized microchannel as compared with the polydimethylsiloxane and glass pristine channels. These results show the viability of functionalized microchannels to mimic xylem vessels and corroborate the important role of chemical environments, and particularly XadA1 adhesin, for early stages of X. fastidiosa biofilm formation, as well as adhesivity modulation along the pathogen life cycle Resumo: FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: D.S.O. received funding from the Brazilian National Council for Scientific and Technological Development (CNPq) Grant 422621/2018-8. M.A.C. received funding from CNPq Grant 429326/2018-1 and from The São Paulo Research Foundation (FAPESP) Grant 2019/07616-3. This research used the computing resources and technical assistance of the John David Rogers Computing Center (CCJDR) in the Institute of Physics "Gleb Wataghin", University of Campinas Abstract: Understanding atomistic mechanisms for catalyst-assisted nanowire growth is an essential step to improve control over the properties of these versatile nanomaterials. However, in silico approaches for III-V nanowire growth have been hindered so far mainly by the limited number of interatomic potentials. Here, we present an original interatomic potential for molecular dynamics simulations of Au-catalyzed GaAs nanowire growth. Our simulations provide important insights about the atomic distribution in the nanowire catalyst and the role of As atoms during GaAs nanowire growth. We show that a stable, thin layer of As around the catalyst is essential for nanowire growth and that the composition of the region close to the solid–liquid interface is nonuniform, alternating between Ga-rich and As/Au-rich layers. These features contribute to the reservoir effect, enlarging interface widths when exchanging group III or V species for heterostructure growth. Our simulation results also provide directions for challenging in situ experiments to further probe the existence of this thin As layer on the catalyst surface, as well as for finding improved conditions to obtain sharp interfaces in nanowires with axial heterostructures CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: We acknowledge the Brazilian Nanotechnology Laboratory (LNNano/CNPEM) for granting access to their electron microscopy facilities, and the Brazilian agency CAPES. B. C. da Silva acknowledges FAPESP for his scholarship (grant 15/24271-9). We also thank M. M. Tanabe for technical support with the optical setup. This work was financially supported by the Brazilian agencies CNPq (grants 305769/2015-4, 432882/2018-9, 479486/2012-3 and 441799/2016-7) and FAPESP (grants 15/16611-4, 12/11382-9 and 16/16365-6) Abstract: Definitive evidence for the direct band gap predicted for Wurtzite Gallium Phosphide (WZ GaP) nanowires has remained elusive due to the lack of strong band-to-band luminescence in these materials. In order to circumvent this problem, we successfully obtained large volume WZ GaP structures grown by nanoparticle-crawling assisted Vapor-Liquid-Solid method. With these structures, we were able to observe bound exciton recombination at 2.14 eV with FHWM of approximately 1 meV. In addition, we have measured the optical absorption edges using photoluminescence excitation spectroscopy. Our results show a 10 K band gap at 2.19 eV and indicate a weak oscillator strength for the lowest energy band-to-band absorption edge, which is a characteristic feature of a pseudo-direct band gap semiconductor. Furthermore, the valence band splitting energies are estimated as 110 meV and 30 meV for the three highest bands. Electronic band structure calculations using the HSE06 hybrid density functional agree qualitatively with the valence band splitting energies COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: This work was partially supported by the Brazilian Institute of Science and Technology (INCT) in Carbon Nanomaterials and the Brazilian agencies CAPES, CNPq (grant 429326/2018-1) and FAPESP (grant 2019/07616-3) Abstract: Semiconductor nanowires are long time candidates for numerous applications. Complete understanding of their most common growth process (vapour-liquid-solid), however, is essential in order to achieve the crystalline quality that applications demand. To date, most of the information gathered to understand vapour-liquid-solid growth comes from ex situ and in situ electron microscopy images. Still, those approaches might miss some important features due to time and length scales involved. In this sense, computational simulations can provide additional insights into the process. Yet, so far, no computational simulation was able to consistently reproduce the growth of more than one monolayer of a semiconductor nanowire through the vapour-liquid-solid method. By using a force matching software (PotFit), we developed a new GaAs interatomic potential for molecular dynamics simulations. Our potential can reproduce several features of the growth of self-catalyzed GaAs nanowires, including: formation of zinc blende and wurtzite layers, layer-by-layer formation of the solid phase, b-polar surface growth preference and the dependency between growth rate and precursor flow COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: The Brazilian authors acknowledge access to electron microscopy (LME) facilities at the National Nanotechnology Laboratory (LNNano, Brazil) and clean room facilities at both Semiconductor Component Center (CCSNano, UNICAMP) and Device Research Laboratory (IFGW, UNICAMP). The Brazilian authors also acknowledge access to the dual beam equipment at CCSNano, UNICAMP, and lithography facilities at LAMULT (IFGW, UNICAMP). We would also like to thank Dr. Richard Janissen (TUDelft) for technical assistance and fruitful discussions. This work was financially supported by the Brazilian agencies FAPESP (grant number 2015/16611-4), CAPES, CNPq (552491/2008-0 and 479486/2012-3) and carried out under the BRICS proposal (CNPq/BRICS - STI 441799/2016-7 and RFBR grant 18-57-70004) Abstract: Fabrication methodologies for integration of nano-objects into microscale devices is still an active area of research. Here we analyze possible methods of incorporation of semiconductor nanowires into lithographically-defined electrode pads. Mechanically-transferred InP nanowires were metallized into Au and Pt pads using a electron-beam-induced Pt metallization. Atomic and Kelvin Probe Force Microscopies show that a contamination of Pt on the nanowire and the region around it can prevent application of this technique to biosensors in which surface functionalization protocols must be applied as part of the fabrication methodology. Other transfer methods with more controlled nanowire positioning, such as nanotweezers, may be necessary to overcome this problem CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: This work was supported by the Brazilian agencies FAPESP grant 2015/16611-4 and CNPq 479486/2012-3. JHM acknowledges scholarship from FAPESP (grant 2013/14888-3) and financial support from UCT-FDI-0182018 project Abstract: In the last decade, hyaluronan (HA, polyanion) and chitosan (CHI, polycation) biopolymers have been assembled by layer-by-layer (LbL) for the synthesis of antibacterial coatings. As electrostatic interactions are the main driving force for the formation of LbL films, pH and ionic strength (IS) are important critical variables of synthesis. In this context, we used surface fractal analysis of HA/CHI films to characterize the growth process for different bilayers obtained with two pH (5 and 3) and IS values (0 and 0.1 M NaCl). Our results showed that the HA/CHI assembling is mainly affected by changes in the pH than IS. Fractal dimension (D-f) of pH 5 series presented values similar to 2.2, indicating that irregularities from the initial random adsorption process are minimized. However, when pH decreased to 3, D-f increases up to similar to 2.5, suggesting a transition to diffusion-limited aggregation FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: We thank Dr Z. Saghi for taking the ADF-STEM images of the twisted wires. D. U. acknowledges financial support from the Brazilian Agencies FAPESP (No. 2014/01045-0) and CNPq (No. 302767/2012-6). A. E. acknowledges funding from the Royal Society. P. A. M. acknowledges financial support from European Research Council through grant 291522-3DIMAGE and the EPSRC grant number EP/R025517/1. M. A. C. acknowledges financial support from FAPESP (Nos. 2013/02300-1 and 2013/10957-0) and CNPq (No. 479486/ 2012-3). L. H. G. T. and P. A. M. acknowledge funding from the European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 312483 (ESTEEM2) Abstract: Transmission electron microscopes (TEM) are widely used in nanotechnology research. However, it is still challenging to characterize nanoscale objects; their small size coupled with dynamical diffraction makes interpreting real- or reciprocal-space data difficult. Scanning precession electron diffraction ((S)PED) represents an invaluable contribution, reducing the dynamical contributions to the diffraction pattern at high spatial resolution. Here a detailed analysis of wurtzite InP nanowires (30-40 nm in diameter) containing a screw dislocation and an associated wire lattice torsion is presented. It has been possible to characterize the dislocation with great detail (Burgers and line vector, handedness). Through careful measurement of the strain field and comparison with dynamical electron diffraction simulations, this was found to be compatible with a Burgers vector modulus equal to one hexagonal lattice cell parameter despite the observed crystal rotation rate being larger (ca. 20%) than that predicted by classical elastic theory for the nominal wire diameter. These findings corroborate the importance of the (S)PED technique for characterizing nanoscale materials CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: The authors acknowledge the support from Multi-User Lab (LAMULT) from Institute of Physics "Gleb Wataghin" at UNICAMP, which provided invalu-able access to their equipments. This work was financially supported FAPEAM, CNPq, and CAPES Abstract: Hyaluronic acid (HA)/chitosan (CHI) films were assembled by LbL using different conditions of pH and ionic strength (IS) in order to obtain stable surfaces to avoid the adhesion and proliferation of Pseudomonas aeruginosa and Staphylococcus aureus. The results showed that pH and IS were key synthesis variables for obtaining different features, such as wettability, thickness and the availability of functional groups. The antibacterial effect was more effective against S. aureus with a reduction of approximately 3, 4, and 1.5 log reduction after 4, 8 and 24 h of culture time, respectively. In the case of P. aeruginosa, the films presented a lower bacterial reduction: 1 log reduction in times evaluated. In conclusion, the results of the antibacterial effect against S. aureus after 24 h, suggest that the HA/CHI films assembled by LbL can protect several substrates, such as biomedical devices, against bacterial proliferation FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO AMAZONAS - FAPEAM CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: The authors acknowledge J. H. Clerici, V. B. Pelegati, and M. O. Baratti for technical assistance, and Prof. H. F. de Carvalho and Prof. A. A. de Thomaz, from the University of Campinas, for valuable discussions. A.C. and E.P.A.M.B. would like to acknowledge Rene Van Veldhoven for the exceptional work and care for the MOVPE systems, and the technical support from the NanoLab@TU/e cleanroom. This work was financially supported by the FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo, Brazil), through grants 2010/51748-7, 2013/02300-1, and 2013/10957-0 and the CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brazil), grant number 479486/2012-3. A.M.d.S. acknowledges scholarship from the CNPq; P.K.S. acknowledges the FAPESP for funding his scholarship. M.A.C., A.A.d.S., and C.L.C. acknowledge the CNPq research fellowships. The authors thank the access to confocal microscopy equipment provided by the National Institute of Science and Technology on Photonics Applied to Cell Biology (INFABIC) at the University of Campinas; INFABIC is cofunded by the FAPESP (08/57906-3) and the CNPq (573913/2008-0). The authors also acknowledge the National Nanotechnology Laboratory (LNNano) at the CNPEM, Brazil, for granting access to their electron microscopy facilities. A.C. and E.P.A.M.B. acknowledge the funding of the Dutch Technology Foundation STW (Project 11826), which is part of the Netherlands Organisation for Scientific Research (NWO), and which is partly funded by the Dutch Ministry of Economic Affairs Abstract: The design and application of indium phosphide (InP) nanowire arrays to acquire Xylella fastidiosa bacterial cell vector force maps are discussed. The nanowire deflections are measured with subdiffraction localization confocal laser scanning microscopy (CLSM). The nanowire mechanical stability in air and liquid media as well as methods to average out thermally induced oscillations are investigated. The accuracy of center determination of the CLSM reflected laser intensity profile at nanowire apex is studied using Gaussian fitting and localization microscopy techniques. These results show that the method is reliable for measuring nanowire displacements above approximate to 25 nm. Corresponding force ranges probed by this method can be customized depending on nanowire geometry and array configuration. The method is applied to explore X. fastidiosa cell adhesion forces on the InP nanowire surface, and in situ probes the effect of N-acetylcysteine on adhered cells. Future perspectives for application of this method in microbiology studies are also outlined FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: This work was supported by the National Council for Scientific and Technological Development (CNPq) - Brazil (grant #479486/2012-3), Sao Paulo Research Foundation (FAPESP) - Brazil (grants #2010/51748-7 and #2013/10957-0), the Natural Sciences and Engineering Research Council (NSERC) and the Research Center of CHU de Quebec. Thiago Taketa would like to thank Sao Paulo Research Foundation (FAPESP) - Brazil, for grant #2013/05135-1 and CAPES - Brazil (Procad 88882.151600/2017-01). Jacobo Herandez-Montelongo would like to thank Sao Paulo Research Foundation (FAPESP) - Brazil for grant #2013/14888-3. Juliana M. Vaz would like to thank National Council for Scientific and Technological Development (CNPq) - Brazil grant number #249963/2013-2 Abstract: Chitosan is a biopolymer with antibacterial properties, which are dependent on its molecular weight (Mw) and its degree of deacetylation (DDA). When grafted on surfaces as a coating, chitosan antibacterial efficiency is also dependent on the polymer chain conformation on the surface, as the amine groups, responsible of the antibacterial effect, should be available for contact with bacteria. To investigate this behavior, chitosans with different Mw were grafted onto plasma aminated surfaces through three different spacers: glutaric anhydride (GA), poly(ethylene-glycol) bis(carboxymethyl) ether (PEGb), and poly (ethylene-alt-maleic anhydride) (PA). The grafting efficiency was evaluated by X-ray Photoelectron Spectroscopy (XPS), contact angle and Rose Bengal test, while morphological features were assessed by profilometry analyses. Results evidenced a clear influence of the anchor arm length and of the Mw of chitosan both on the grafting efficiency and on the antibacterial behavior. PA CHIMW surface exhibited a better antibacterial response compared to GA and PEGb, which could be correlated to a denser coating coverage as seen by XPS and profilometry results. Further, PA CHIMW coating displayed a higher amine density, thus promoting the interaction with the bacteria cell wall. Based on these results, chitosan-based coatings can then be extended to a wide range of antibacterial applications CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: We acknowledge the Brazilian Nanotechnology National Laboratory (LNNano, CNPEM) for access to their XPS facilities. This work was financially supported by FAPESP (grants # 2013/14888-3 and 2015/16611-4), CNPq and CAPES Abstract: Staphylococcus epidermidis is a gram-positive bacterium, and one of the most prevalent causes of nosocomial infections due to its strong ability to form biofilms on catheters and surgical implants. Here we explore the antimicrobial properties of Tet-124 peptides, which are part of the innate defense against different multicellular organisms in nature. Two different Tet-124 peptides were immobilized on a polyethylenimine (PEI) film to determine their impact on the antimicrobial properties: KLWWMIRRW (Tet-124), which contains only natural amino acids, and KLWWMIRRWG-(F-Br)-G (F-Br- 4-Bromophenylalanine), a modified Tet-124 sequence with the addition of an unnatural amino acid. The immobilization was obtained as a result of the electrostatic interaction between PEI amino groups and the C-terminal carboxylic groups of tryptophan and glycine amino acids of Tet-124 and Tet-124-Br peptides, respectively. The process was monitored and studied by water contact angle, Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and Quartz Crystal Microbalance with Dissipation (QCM-D) measurements. The antibacterial effect of our samples against S. epidermis was evaluated by the spread plate counting method, and cytotoxicity was tested using fibroblast cultures. Our results indicate the feasibility to immobilize electrostatically both Tet-124 peptides for biomedical applications FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Aberto

Agradecimentos: This work was financially supported by Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (grant numbers 2010/51748-7 and 2013/02300-1), Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (307139/2015-8), Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior and Fundacao de Amparo a Pesquisa do Estado de Minas Gerais. J. Hernandez-Montelongo and V. Nascimento acknowledge FAPESP and FAPEAM scholarships, respectively Abstract: In recent years, a common strategy, to obtain more uniform and controlled synthesis of polyelectrolytes multi layers (PEMs), relies on a previous polyethylenimine (PEI) coating of the substrate surface. PEI is a synthetic cationic polymer which provides a positive charge distribution on the materials to be covered with PEMs. Despite being an important step, this pre-layer deposition is frequently overlooked and no comprehensive characterizations or deep discussions are reported in literature. In that sense, this work reports on the synthesis of a typical PEI film that works as a precursor for PEMs, and its detailed physicochemical characterization. As many PEMs are produced for antibacterial and biomedical applications, the cytotoxicity of the film was also tested using fibroblasts, and its antibacterial activity was studied using Staphylococcus aureus and Pseudomonas aeruginosa. Our results present the formation of an ultra-thin film of PEI with a thickness around 3.5 nm, and with a significant percent of NH3+ (35% of the total amount of N) in its chemical structure; NH3+ is a key chemical group because it is considered an important bacterial killer agent. The film was stable and did not present important cytotoxic effect for fibroblasts up to 7 days, contrary to other reports. Finally, the PEI film showed high antibacterial activity against the S. aureus strain: reductions in cell density were higher than 95% up to 24 h FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIG FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO AMAZONAS - FAPEAM Fechado

Agradecimentos: R.J., P.K.S. and D.S.O. acknowledge scholarships from FAPESP and A.M.S. and D.B.A. from CAPES/CNPq. Access to confocal microscopy was granted by INFABIC/UNICAMP (FAPESP 08/57906-3, CNPq 573913/2008-0). We acknowledge access to electron microscopy (LME) and microfabrication (LMF) facilities at the National Nanotechnology Laboratory (LNNano, Brazil) and clean room facilities at both Semiconductor Component Center (CCSNano, UNICAMP) and Device Research Laboratory (IFGW, UNICAMP). Xf.XadA2 antibodies were provided by Dr. A. A. de Souza (IAC, Cordeirópolis, São Paulo, Brazil). The authors are greatly indebted to A. Gobbi and M.H. Piazzetta from LMF/LNNano for PDMS microfluidics processing, Dr. A. Kisner from IQ/UNICAMP and P .C. Galvão, from IQ/UNESP, for technical assistance during this work Abstract: Electrically active field-effect transistors (FET) based biosensors are of paramount importance in life science applications, as they offer direct, fast, and highly sensitive label-free detection capabilities of several biomolecules of specific interest. In this work, we report a detailed investigation on surface functionalization and covalent immobilization of biomarkers using biocompatible ethanolamine and poly(ethylene glycol) derivate coatings, as compared to the conventional approaches using silica monoliths, in order to substantially increase both the sensitivity and molecular selectivity of nanowire-based FET biosensor platforms. Quantitative fluorescence, atomic and Kelvin probe force microscopy allowed detailed investigation of the homogeneity and density of immobilized biomarkers on different biofunctionalized surfaces. Significantly enhanced binding specificity, biomarker density, and target biomolecule capture efficiency were thus achieved for DNA as well as for proteins from pathogens. This optimized functionalization methodology was applied to InP nanowires that due to their low surface recombination rates were used as new active transducers for biosensors. The developed devices provide ultrahigh label-free detection sensitivities similar to 1 fM for specific DNA sequences, measured via the net change in device electrical resistance. Similar levels of ultrasensitive detection of similar to 6 fM were achieved for a Chagas Disease protein marker (IBMP8-1). The developed InP nanowire biosensor provides thus a qualified tool for detection of the chronic infection stage of this disease, leading to improved diagnosis and control of spread. These methodological developments are expected to substantially enhance the chemical robustness, diagnostic reliability, detection sensitivity, and biomarker selectivity for current and future biosensing devices FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: This work was financially supported by the Brazilian agencies FAPESP (grants 2013/02300-1, 2016/16365-6, 2011/50975-2, 2012/22617-7 and 2015/16611-4) and CNPq (grants 479486/2012-3, 475343/2013-1 and 305769/20154) as well as the Spanish Ministry of Science and Innovation (grant MAT2009-10350). D S Oliveira and P K Sahoo acknowledge FAPESP for funding their scholarships. A. Molina-Sanchez acknowledges the Luxembourg National Research Fund, project C14/MS/7731521, FAST-2DMAT. The authors also acknowledge the National Laboratory of Nanotechnology (LNNANO/CNPEM, Brazil) for granting access to electron microscopy facilities Abstract: InAs nanowires grown by vapor-liquid-solid (VLS) method are investigated by photoluminescence. We observe that the Fermi energy of all samples is reduced by similar to 20 meV when the size of the Au nanoparticle used for catalysis is increased from 5 to 20 nm. Additional capping with a thin InP shell enhances the optical emission and does not affect the Fermi energy. The unexpected behavior of the Fermi energy is attributed to the differences in the residual donor (likely carbon) incorporation in the axial (low) and lateral (high incorporation) growth in the VLS and vapor-solid (VS) methods, respectively. The different impurity incorporation rate in these two regions leads to a core/shell InAs homostructure. In this case, the minority carriers (holes) diffuse to the core due to the built-in electric field created by the radial impurity distribution. As a result, the optical emission is dominated by the core region rather than by the more heavily doped InAs shell. Thus, the photoluminescence spectra and the Fermi energy become sensitive to the core diameter. These results are corroborated by a theoretical model using a self-consistent method to calculate the radial carrier distribution and Fermi energy for distinct diameters of Au nanoparticles FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: The authors acknowledge technical assistance from Vitor Pelegatti, from INFABIC/UNICAMP, Maria H. Piazetta and A.Gobbi, from LNNano/CNPEM. The authors are also greatly indebted to Dr. Richard Janissen, from Kavli Institute of Nanoscience, Delft University of Technology, and M.Sc. Duber Murillo from Applied Physics Department at the State University of Campinas, for fruitful discussions during this work Abstract: The pathogenicity of Xylella fastidiosa is associated with its systematic colonization of the plant xylem, forming bacterial biofilms. Mechanisms of bacterial transport among different xylem vessels, however, are not completely understood yet, but are strongly influenced by the presence of extracellular polymeric substances (EPS), which surrounds the assembly of cells forming the biofilm. In this work, we show quantitative measurements on the elastic properties of the system composed by EPS and bacterial cell. In order to investigate the mechanical properties of this system, force spectroscopy and confocal Raman measurements were carried out during Xylella fastidiosa subsp. pauca initial stages of adhesion and cluster formation. We show that stiffness progressively decreases with increasing culture growth time, from two to five days. For early adhesion samples, stiffness values are quite different at the bacterial polar and body regions. Lower stiffness values at the cell pole suggest a flexible mechanical, response at this region, associated with first cell adhesion to a surface. These results correlate very well with our observations of cell motion within microchannels, under conditions simulating xylem flow. Both the oscillatory movement of vertically attached single cells, as well as the transport of cell clusters within the biofilm matrix can be explained by the presence of softer materials at the cell pole and EPS matrix. Our results may thus add to a more detailed understanding of mechanisms used by cells to migrate among vessels in plant xylem FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: We acknowledge the Brazilian Nanotechnology Laboratory (LNNANO/CNPEM) for granting access to their electron microscopy facilities. We also acknowledge H T Obata for technical assistance with CBE growth. This work was financially supported by FAPESP (grants 2013/02300-1, 2016/16365-6 and 2015/16611-4) and CNPq (grant 479486/20123, 305769/2015-4). DSO and MZ acknowledge FAPESP and CAPES, respectively, for funding their scholarships. This work has also received support from the French state managed by the National Agency for Research under the program of future investment EQUIPEX TEMPOS-NANOTEM with the reference ANR-10-EQPX-50 Abstract: We report on the existence of two different regimes in one-step Ag-seeded InP nanowire growth. The vapor-liquid-solid-mechanism is present at larger In precursor flows and temperatures, similar to 500 degrees C, yielding high aspect ratio and pure wurtzite InP nanowires with a semi-spherical metal particle at the thin apex. Periodic diameter oscillations can be achieved under extreme In supersaturations at this temperature range, showing the presence of a liquid catalyst. However, under lower temperatures and In precursor flows, large diameter InP nanowires with mixed wurtzite/zincblende segments are obtained, similarly to In-assisted growth. Chemical composition analysis suggest that In-rich droplet formation is catalyzed at the substrate surface via Ag nanoparticles; this process might be facilitated by the sulfur contamination detected in these nanoparticles. Furthermore, part of the original Ag nanoparticle remains solid and is embedded inside the actual catalyst, providing an in situ method to switch growth mechanisms upon changing In precursor flow. Nevertheless, our Ag-seeded InP nanowires exhibit overall optical emission spectra consistent with the observed structural properties and similar to Au-catalyzed InP nanowires. We thus show that Ag nanoparticles may be a suitable replacement for Au in InP nanowire growth FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: We acknowledge the Brazilian Nanotechnology Laboratory (LNNano/CNPEM) and Laboratory of Structural Characterization (LCS/UFSCAR) for granting access to their electron microscopy facilities. B.C.d.S. acknowledges FAEPEX-UNICAMP and CAPES for scholarships. We also acknowledge D. M. Ugarte for discussions on transmission electron microscopy, H.T. Obata for technical assistance with CBE system, and S. R. Araujo for lamella preparation. This work was financially supported by the Brazilian agencies CAPES, CNPq (Grants 479486/2012-3, 305769/2015-4, and 2012/10127-5), and FAPESP (Grants 2012/11382-9, 2013/02300-1, 2014/23399-9, 2015/16611-4, and 2016/16365-6) Abstract: Here we show a new nanowire growth procedure, exploring the thermally activated motion of Au droplets on III-V surfaces. We show that by setting a single growth parameter we can activate the crawling motion of Au droplets in vacuum and locally modify surface composition in order to enhance vapor solid (VS) growth along oxide-free areas on the trail of the metal particle. Asymmetric VS growth rates are comparable in magnitude to the vapor liquid solid growth, producing unconventional wurtzite GaP morphologies, which shows negligible defect density as well as optical signal in the green spectral region. Finally, we demonstrate that this effect can also be explored in different substrate compositions and orientations with the final shape finely tuned by group III flow and nanoparticle size. This distinct morphology for wurtzite GaP nanomaterials can be interesting for the design of nanophotonics devices COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: We would like to thank Analytical Resources and Calibration Laboratory (LRAC) from Faculty of Chemical Engineering and Multi-user Lab (LAMULT) from Institute of Physics "Gleb Wataghin", both from UNICAMP, for providing the analytical facilities. We would also like to thank the National Nanotechnology Laboratory (LNNano) for granting access to the electron microscopy facilities. This work was financially supported by FAPESP (grant numbers 2010/51748-7 and 2013/02300-1), CNPq and CAPES. J. Hernandez-Montelongo and V. Nascimento acknowledge FAPESP and FAPEAM scholarships, respectively Abstract: In the last few years, chitosan-based coatings have been proposed as antibacterial surfaces for biomedical devices in order to prevent nosocomial infections. In that sense, this work reports the optimized synthesis of hyaluronan/chitosan (HA/CHI) nanofilms assembled layer-by-layer in order to maximize the antibacterial effect for two important human pathogenic bacteria, Staphylococcus aureus and Pseudomonas aeruginosa. In this assembly, HA forms a soft, highly hydrated, and nontoxic film, whereas CHI shows the antimicrobial characteristics. Our HA/CHI nanofilm synthesis optimization was based on changing pH values of the biopolymer stem-solutions and the consequent variation of their ionization degree. Furthermore, the surface density of primary amino groups, which are related to the antibacterial effect, was also enhanced by increasing the number of HA/CHI bilayers. The antibacterial effect of HA/CHI nanofilms was evaluated by the spread plate counting method for both bacteria. These results were correlated with the morphology of nanofilms (characterized using SEM and AFM), as well as with their chemical properties studied by UV–vis, Kelvin Probe Force microscopy and XPS spectroscopy FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: The authors acknowledge J. H. Clerici, V. B. Pelegati, and M. O. Baratti for technical assistance and C. B. Santos and Prof. A. P. de Souza, from CBMEG/UNICAMP for providing the XadA1 protein. A.C. and E.P.A.M.B. would like to acknowledge Rene Van Veldhoven for the exceptional work and care for the MOVPE systems and the technical support from the Nano-Lab@TU/e cleanroom. This work was financially supported by FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo, Brazil), through grants 2010/51748-7 and 2013/02300-1, and CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brazil), grant number 479486/2012-3. D.M.M. and M.P.M. acknowledge scholarships from CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior, Brazil); P.K.S. and R.J. acknowledge FAPESP for funding their scholarships. M.A.C., A.A.S., and H.F.C. acknowledge CNPq fellowships. The authors thank the access to confocal microscopy equipment provided by the National Institute of Science and Technology on Photonics Applied to Cell Biology (INFABIC) at the State University of Campinas; INFABIC is cofunded by FAPESP (08/57906-3) and CNPq (573913/2008-0). We also acknowledge the National Nano technology Laboratory (LNNano) at CNPEM, Brazil, for granting access to their electron microscopy facilities. A.C. and E.P.A.M.B. acknowledge the funding of the Dutch Technology Foundation STW (Project 11826), which is part of The Netherlands Organisation for Scientific Research (NWO), and which is partly funded by the Dutch Ministry of Economic Affairs Abstract: Surface attachment of a planktonic bacteria, mediated by adhesins and extracellular polymeric substances (EPS), is a crucial step for biofilm formation. Some pathogens can modulate cell adhesiveness, impacting host colonization and virulence. A framework able to quantify cell-surface interaction forces and their dependence on chemical surface composition may unveil adhesiveness control mechanisms as new targets for intervention and disease control. Here we employed InP nanowire arrays to dissect factors involved in the early stage biofilm formation of the phytopathogen Xylella fastidiosa. Ex vivo experiments demonstrate single-cell adhesion forces up to 45 nN, depending on the cell orientation with respect to the surface. Larger adhesion forces occur at the cell poles; secreted EPS layers and filaments provide additional mechanical support. Significant adhesion force enhancements were observed for single cells anchoring a biofilm and particularly on XadA1 adhesincoated surfaces, evidencing molecular mechanisms developed by bacterial pathogens to create a stronger holdfast to specific host tissues FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Aberto

Agradecimentos: The authors acknowledge the support from Analytical Resources and Calibration Laboratory (LRAC) from Chemical Engineering Department and the Multi-User Lab (LAMULT) from Institute of Physics "Gleb Wataghin", both at UNICAMP, which provided invaluable access to their equipments. We would also like to thank the National Nanotechnology Laboratory (LNNano) for granting access to the electron microscopy facilities. This work was financially supported by FAPESP (grant numbers 2010/51748-7 and 2013/02300-1), CNPq and CAPES. J. Hernandez-Montelongo and P. Sahoo acknowledge FAPESP scholarships; FAPEAM and CAPES provide the scholarships to V. Nascimento and D. Murillo, respectively Abstract: In this work, nanofilms of hyaluronan/chitosan (HA/CHI) assembled layer by layer were synthesized; their application as a potential antimicrobial material was demonstrated for the phytopathogen Xylella fastidiosa, a gram-negative bacterium, here used as a model. For the synthesis, the influence of pH and ionic strength of these natural polymer stem-solutions on final characteristics of the HA/CHI nanofilms was studied in detail. The antibacterial effect was evaluated using widefield fluorescence microscopy. These results were correlated with the chemical properties of the nanofilms, studied by FTIR and Raman spectroscopy, as well as with their morphology and surface properties characterized using SEM and AFM. The present findings can be extended to design and optimize HA/CHI nanofilms with enhanced antimicrobial behavior for other type of phytopathogenic gram-negative bacteria species, such as Xanthomonas citri, Xanthomas campestri and Ralstonia solanacearum FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO AMAZONAS - FAPEAM Fechado

Agradecimentos: We gratefully acknowledge the Laboratório de Espectroscopia e Calorimetria (LEC) and Laboratório Nacional de Biociências—LNBio (Campinas, Brazil) for their support with the circular dichroism assays and to the Brazilian Nanotechnology National Laboratory LNNano for helping us with the analysis of the AFM images and to the Field Emission Scanning Electron Microscopy—FESEM, Chemistry Institute, Unicamp, Campinas. Also, we are grateful to the staff of the Life Sciences Core Facility (LaCTAD) from the State University of Campinas (UNICAMP) for the ITC analysis. We also would like to thank to the professor Paulo Pinto Joazeiro of the Structural and Cell Biology Department of the Biology Institute from Unicamp. The authors gratefully acknowledge the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Process 2012/51580-4 and 2001/07533-7) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Computational Biology Program). ASS was partially supported by a Ph.D. fellowship from FAPESP (Process 2011/50268-4) and CAPES (Computational Biology Program), CS is the recipient of a postdoctoral fellowship Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and APS is the recipient of a research fellowship from CNPq Abstract: The Xylella fastidiosa subsp pauca strain 9a5c is a Gram-negative, xylem-limited bacterium that is able to form a biofilm and affects citrus crops in Brazil. Some genes are considered to be involved in biofilm formation, but the specific mechanisms involved in this process remain unknown. This limited understanding of how some bacteria form biofilms is a major barrier to our comprehension of the progression of diseases caused by biofilm-producing bacteria. Several investigations have shown that the toxin-antitoxin (TA) operon is related to biofilm formation. This operon is composed of a toxin with RNAse activity and its cognate antitoxin. Previous reports have indicated that the antitoxin is able to inhibit toxin activity and modulate the expression of the operon as well as other target genes involved in oxidative stress and mobility. In this study, we characterize a toxin antitoxin system consisting of XfMqsR and XfYgiT, respectively, from X. fastidiosa subsp. pauca strain 9a5c. These proteins display a high similarity to their homologs in X fastidiosa strain Temecula and a predicted tridimensional structure that is similar to MqsR-YgiT from Escherichia coli, The characterization was performed using in vitro assays such as analytical ultracentrifugation (AUC), size exclusion chromatography, isothermal titration calorimetry, and Western blotting. Using a fluorometric assay to detect RNAses, we demonstrated that XfMqsR is thermostable and can degrade RNA. XfMqsR is inhibited by XfYgiT, which interacts with its own promoter. XfYgiT is known to be localized in the intracellular compartment, however, we provide strong evidence that X. fastidiosa secretes wild-type XfYgiT into the extracellular environment via outer membrane vesicles, as confirmed by Western blotting and specific immunofluorescence labeling visualized by fluorescence microscopy. Taken together, our results characterize the TA system from X. fastidiosa strain 9a5c, and we also discuss the possible influence of wild-type XfYgiT in the cell CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: This study was supported by grants from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, 2012/51580-4 and 2001/07533-7). C.A.S. was the recipient of a Ph.D. fellowship from FAPESP (Process 2008/55690-3); R.J. acknowledges postdoctoral FAPESP scholarship (2009/53021-0). A.P.S. and M.A.C. are the recipients of a research fellowship from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). We gratefully acknowledge the Laboratório Nacional de Luz Síncrotron (LNLS, Campinas, Brazil) for providing beamline time. We thank Alessandra P. de Souza of the APTA Citrus ‘Sylvio Moreira’ Center, Agronomic Institute of Campinas, Cordeirópolis, SP, Brazil for the assistance with X. fastidiosa biofilms and Prof. Dr. Carlos H. I. Ramos of the Institute of Chemistry, University of Campinas, Campinas, SP, Brazil for providing anti-Hsp70/Hsc70 — Global antibody Abstract: The intriguing roles of the bacterial Tol-Pal trans-envelope protein complex range from maintenance of cell envelope integrity to potential participation in the process of cell division. In this study, we report the characterization of the XfFolB and XfPal proteins of the Tol-Pal complex of Xylella fastidiosa. X. fastidiosa is a major plant pathogen that forms biofilms inside xylem vessels, triggering the development of diseases in important cultivable plants around the word. Based on functional complementation experiments in Escherichia coli tolB and pal mutant strains, we confirmed the role of xftolB and xfpal in outer membrane integrity. In addition, we observed a dynamic and coordinated protein expression profile during the X. fastidiosa biofilm development process. Using small-angle X-ray scattering (SAXS), the low-resolution structure of the isolated XfToIB-XfPal complex in solution was solved for the first time. Finally, the localization of the XfFolB and XfPal polar ends was visualized via immunofluorescence labeling in vivo during bacterial cell growth. Our results highlight the major role of the components of the cell envelope, particularly the TolB-Pal complex, during the different phases of bacterial biofilm development FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: We acknowledge the National Laboratory of Nanotechnology (LNNANO/CNPEM) for granting access to their electron microscopy facilities. We also acknowledge Th. Chiaramonte for discussions on NW growth and H. T. Obata for technical assistance. This work was financially supported by FAPESP (grant 2013/02300-1), CNPq (grant 479486/2012-3) and CAPES. D.S. Oliveira acknowledges FAPESP for funding his scholarship Abstract: Semiconductor nanowires oriented along the [211] direction usually present twins parallel to their axis. For group IV nanowires this kind of twin allows the formation of a catalyst-nanowire interface composed of two equivalent {111} facets. For III-V nanowires, however, the twin will generate two facets with different polarities. In order to keep the < 211 > orientation stable, a balance in growth rates for these different facets must be reached. We report here the observation of stable, micron-long < 211 >-oriented InGaP nanowires with a spontaneous core-shell structure. We show that stacking fault formation in the crystal region corresponding to the {111} A facet termination provides a stable NW/NP interface for growth along the < 211 > direction. During sample cool down, however, the catalyst migrates to a lateral {111} B facet, allowing the growth of branches perpendicular to the initial orientation. In addition to that, we show that the core-shell structure is non-concentric, most likely due to the asymmetry between the facets formed in the NW sidewall; this effect generates stress along the nanowire, which can be relieved through bending FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: One of us (A.P.) thanks the Department of Atomic Energy, India, for financial aid. The authors acknowledge the expertise of R. Pandian, SND, for FESEM studies. We also thank S. Chandra and P. Jagadeesan of MPD, IGCAR, for useful discussions in the simulation studies. The UGC-DAE CSR, Kalpakkam node, is acknowledged for the computation and electron microscopy facility Abstract: The physicochemical processes at the surfaces of semiconductor nanostructures involved in electrochemical and sensing devices are strongly influenced by the presence of intrinsic or extrinsic defects. For revelation of the surface controlled sensing mechanism, intentional lattice oxygen defects are created on the surfaces of GaN nanowires for the elucidation of charge transfer process in methane (CH4) sensing. Experimental and simulation results of electron energy loss spectroscopy (EELS) studies on oxygen rich GaN nanowires confirmed the possible presence of 2(O-N) and V-Ga-3O(N) defect complexes. A global resistive response for sensor devices of ensemble nanowires and a localized charge transfer process in single GaN nanowires are studied by in situ scanning Kelvin probe microscopy (SKPM). A localized charge transfer process, involving the V-Ga-3O(N) defect complex on a nanowire surface, is attributed to controlling the global gas sensing behavior of the oxygen rich ensemble GaN nanowires Aberto

Agradecimentos: This work has received support from CNPq, from 2007/58962-1, 2008/55023-7, 2011/05989-5, Sao Paulo Research Foundation (FAPESP), from the National Agency for Research under the program of future investment TEMPOS-CHROMATEM with the reference no ANR-10-EQPX-50 and from the European Union Seventh Framework Programme (No FP7/2007-2013) under Grant agreement no n312483 (ESTEEM2) Abstract: We report the observation of light emission on wurtzite InP nanowires excited by fast electrons. The experiments were performed in a scanning transmission electron microscope using an in-house-built cathodoluminescence detector. Besides the exciton emission, at 850 nm, emission above the band gap from 400 to 800 nm was observed. In particular, this broad emission presented systematic periodic modulations indicating variations in the local excitation probability. The physical origin of the detected emission is not clear. Measurements of the spatial variation of the above-the-gap emission points to the formation of leaky cavity modes of a plasmonic nature along the nanowire length, indicating the wave nature of the excitation. We propose a phenomenological model, which fits closely the observed spatial variations CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: The authors thank CAPES, CNPq and FAPESP (2006/58998-3, 2008/51001-9, 2009/50596-1 and 2010/18656-1) for financial support; LME/LNLS for technical support during the electron microscopy work and LMF/LNLS for providing platinized counter-electrodes. We also thank Prof. Carol Collins for English revision Abstract: TiO2–MWCNT composite electrodes were prepared by a direct mixing method. The presence of acid-treated multi-wall carbon nanotubes (MWCNT–COOH) into the titanium dioxide (TiO2) photoanode was investigated by Raman spectroscopy and X-ray diffraction (XRD). The morphological properties of the composite photoanodes were analyzed by field emission scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The performance of quasi-solid state dye-sensitized solar cells (DSSC) using TiO2–MWCNT photoanodes was dependent on the MWCNT loading. Compared with a DSSC based on conventional TiO2 electrodes, the TiO2–MWCNT film containing 0.02 wt.% of carbon nanotubes provided an increase of ca. 30% in device's efficiency, which was attributed to an enhanced short-circuit current density (Jsc). The improvement on Jsc was correlated with an enhanced interconnectivity between MWCNT–COOH and TiO2 nanoparticles. The carbonaceous materials introduced an alternative electrical conduction pathway which facilitates rapid electron transport in the photoelectrode, as suggested from Kelvin probe force microscopy (KPFM) measurements. At high MWCNT loading, we observed that the energy conversion efficiency decreased due to energy losses from the optical absorption of carbonaceous materials, and also due to an increase in charge recombination COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: We thank the Spanish Ministry of Science and Innovation (grant Nos TEC2009-12075 and MAT2009-10350), CNPq, CAPES, FAPESP for financial support and P Motisuke, R L Carvalho and M J S P Brasil for experimental support. We also thank the Electron Microscopy Laboratory (LME) at the Brazilian Synchrotron Light Laboratory for support during microscopy experiments Abstract: Wurtzite InAs nanowire samples grown by chemical beam epitaxy have been analyzed by photoluminescence spectroscopy. The nanowires exhibit two main optical emission bands at low temperatures. They are attributed to the recombination of carriers in quantum well structures, formed by zincblende-wurtzite alternating layers, and to the donor-acceptor pair. The blue-shift observed in the former emission band when the excitation power is increased is in good agreement with the type-II band alignment between the wurtzite and zincblende sections predicted by previous theoretical works. When increasing the temperature and the excitation power successively, an additional band attributed to the band-to-band recombination from wurtzite InAs appears. We estimated a lower bound for the wurtzite band gap energy of approximately 0.46 eV at low temperature CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: The authors wish to thank the Institute for Energy and Nuclear Research/IPEN-CNEN in São Paulo, Brazil, for the use of its irradiation facilities. This study was supported by FAPESP and CNPq, Brazilian funding agencies Abstract: Double-stranded pBS plasmid DNA was irradiated with gamma rays at doses ranging from 1 to 12 kGy and electron beams from 1 to 10 kGy. Fragment-size distributions were determined by direct visualization, using atomic force microscopy with nanometer-resolution operating in non-tapping mode, combined with an improved methodology. The fragment distributions from irradiation with gamma rays revealed discrete-like patterns at all doses, suggesting that these patterns are modulated by the base pair composition of the plasmid. Irradiation with electron beams, at very high dose rates, generated continuous distributions of highly shattered DNA fragments, similar to results at much lower dose rates found in the literature. Altogether, these results indicate that AFM could supplement traditional methods for high-resolution measurements of radiation damage to DNA, while providing new and relevant information FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: This work was supported by grants from FAPESP and CNPq, Brazilian agencies for the promotion of science Abstract: Persistent harmful scenarios associated with disposal of radioactive waste, high-background radiation areas and severe nuclear accidents are of great concern regarding consequences to both human health and the environment. Of particular concern is the extracellular DNA in aquatic environments contaminated by radiological substances. Strand breaks induced by radiation promote decrease in the transformation efficiency for extracellular DNA. The focus of this study is the quantification of DNA damage following long-term exposure (over one year) to low doses of natural uranium (an alpha particle emitter) to simulate natural conditions, since nothing is known about alpha radiation induced damage to extracellular DNA. A high-resolution Atomic Force Microscope was used to evaluate DNA fragments. Double-stranded plasmid pBS as a model for extracellular DNA was exposed to different amounts of natural uranium. It was demonstrated that low concentrations of U in water (50 to 150 ppm) produce appreciable numbers of double strand breaks, scaling with the square of the average doses. The importance of these findings for environment monitoring of radiological pollution is addressed FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: This work was financially supported by FAPESP (Fundação de Amparo a Pesquisa do Estado de Sao Paulo) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico). A.L.D.M. and R.J. acknowledge scholarships from CNPq and FAPESP, respectively Abstract: The development of highly-sensitive and label-free operating semiconductor-based, biomaterial detecting sensors has important applications in areas such as environmental science, biomedical research and medical diagnostics. In the present study, we developed an Indium Phosphide (InP) semiconductor-based resistive biosensor using the change of its electronic properties upon biomaterial adsorption as sensing element. To detect biomaterial at low concentrations, the procedure of functionalization and covalent biomolecule immobilization was also optimized to guarantee high molecule density and high reproducibility which are prerequisite for reliable results. The characterization, such as biomolecular conjugation efficiency, detection concentration limits, recepton:ligand specificity and concentration detection range was analyzed by using three different biological systems: i) synthetic dsDNA and two phytopathogenic diseases, ii) the severe CB-form of Citrus Tristeza Virus (CIV) and iii) Xylella fastidiosa, both causing great economic loss worldwide. The experimental results show a sensitivity of 1 pM for specific ssDNA detection and about 2 nM for the specific detection of surface proteins of CTV and X fastidiosa phytopathogens. A brief comparison with other semiconductor based biosensors and other methodological approaches is discussed and confirms the high sensitivity and reproducibility of our InP based biosensor which could be suitable for reliable early infection diagnosis in environmental and life sciences FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: The authors gratefully acknowledge the financial support of the Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP (São Paulo, Brazil). We also thank the Laboratório de Espectroscopia e Calorimetria (LEC), Laboratório Nacional de Biociências – LNBio (Campinas, Brazil), for the support on the circular dichroism studies and Professor Maricilda Palandi de Mello, CBMEG, UNICAMP (Campinas, Brazil), for the support on the HeLa cells culture. Finally, the authors thank Professor Ricardo Aparício, IQ, UNICAMP, for the help with the preliminary studies of SAXS and Professor Lucimara Gaziola de la Torre, FEQ, UNICAMP, for the help with potential zeta and particle size measurements Abstract: The low efficiency of gene transfer is a recurrent problem in DNA vaccine development and gene therapy studies using non-viral vectors such as plasmid DNA (pDNA). This is mainly due to the fact that during their traffic to the target cell's nuclei, plasmid vectors must overcome a series of physical, enzymatic and diffusional barriers. The main objective of this work is the development of recombinant proteins specifically designed for pDNA delivery, which take advantage of molecular motors like dynein, for the transport of cargos from the periphery to the centrosome of mammalian cells. A DNA binding sequence was fused to the N-terminus of the recombinant human dynein light chain LC8. Expression studies indicated that the fusion protein was correctly expressed in soluble form using E. coli BL21(DE3) strain. As expected, gel permeation assays found the purified protein mainly present as dimers, the functional oligomeric state of LC8. Gel retardation assays and atomic force microscopy proved the ability of the fusion protein to interact and condense pDNA. Zeta potential measurements indicated that LC8 with DNA binding domain (LD4) has an enhanced capacity to interact and condense pDNA, generating positively charged complexes. Transfection of cultured HeLa cells confirmed the ability of the LD4 to facilitate pDNA uptake and indicate the involvement of the retrograde transport in the intracellular trafficking of pDNA:LD4 complexes. Finally, cytotoxicity studies demonstrated a very low toxicity of the fusion protein vector, indicating the potential for in vivo applications. The study presented here is part of an effort to develop new modular shuttle proteins able to take advantage of strategies used by viruses to infect mammalian cells, aiming to provide new tools for gene therapy and DNA vaccination studies FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: This work was supported by Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP), Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) and Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES). RA, MAC and APS were also supported by a researcher grant from CNPq. We gratefully acknowledge LNLS for W01B-MX2 beamline time and LNBio for use of the Honeybee 963 Pipettor robot facility Abstract: The ORF XF2234 in the Xylella fastidiosa genome was identified as encoding a small heat-shock protein of 17.9 kDa (HSP17.9). HSP17.9 was found as one of the proteins that are induced during X. fastidiosa proliferation and infection in citrus culture. Recombinant HSP17.9 was crystallized and surface atomic force microscopy experiments were conducted with the aim of better characterizing the HSP17.9 crystals. X-ray diffraction data were collected at 2.7 angstrom resolution. The crystal belonged to space group P4(3)22, with unit-cell parameters a = 68.90, b = 68.90, c = 72.51 angstrom, and is the first small heat-shock protein to crystallize in this space group FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Aberto

We investigated two stacked layers of InP/GaAs type-II quantum dots by transmission electron microscopy and optical spectroscopy. The results reveal that InP quantum dots formed in two quantum dot layers are more uniform than those from a single layer structure. The thermal activation energies as well as the photoluminescence decays are rather independent of the separation between quantum dot layers and the presence of the second layer. The quantum dot optical emission persists for thermal activation energy larger than the calculated exciton binding energy. The hotoluminescence decay is relatively fast for type-II alignment FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

The influence of four different materials (glass, stainless steel, polytetrafluoroethylene PTFE and polyamide) used as a paste drying support on the detachment conditions of dried maltodextrin films was investigated. The tests were accomplished in a drying chamber that allows the spreading of a uniform film of pastelike material over solid plates and the visual observation of the instant of the detachment from the surface. The chamber temperature and the water content of the dried film were compared with the corresponding glass transition temperature curve. The effect of the material roughness on the detachment of the dried maltoclextrin film was evaluated comparing glass plates with two different surfaces (smooth and sand-blasted glass). Results indicate that the higher the surface roughness, the drier should the film be, in order to promote self-detachment at the same temperature conditions. The chemical and physical interactions between the support material and the dried film also influence the process. The PTFE support required less severe detachment conditions than solids with lower surface roughness COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: The authors thank J. H. Clerici and K. O. Vicaro for helpful support in AFM measurements, Milton M. Tanabe for technical support, CME-UFRGS for TEM measurements, and the Brazilian Synchrotron Laboratory (Laboratório Nacional de Luz Sincrotron—LNLS) for GID measurements. We also acknowledge the financial support from CAPES, CNPq, FAPESP, and FAEP Abstract: We investigated structural and optical properties of type-II InP/GaAs quantum dots using reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction, and photoluminescence techniques. The InP dots present an efficient optical emission even when they are uncapped, which is attributed to the low surface recombination velocity in InP. We compare the difference in the optical properties between surface free dots, which are not covered by any material, with dots covered by a GaAs capping layer. We observed a bimodal dispersion of the dot size distribution, giving rise to two distinct emission bands. The results also revealed that the strain accumulated in the InP islands is slightly relieved for samples with large InP amounts. An unexpected result is the relatively large blue shift of the emission band from uncapped samples as compared to capped dots COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: This work was supported by the Brazilian Agencies FAPESP, CNPq, and FINEP. Two of the authors (J.R.R.B. and H.R.G.) acknowledge financial support from FAPESP. TEM measurements were carried out at the LME facilities of the Brazilian Synchrotron Light Laboratory (LNLS), Brazil. We also thank R. Marcon for technical assistance with the XRD measurements and J. G. Zelcovit for TEM sample preparation Abstract: We investigate the formation of compositional modulation and atomic ordering in InGaP films. Such bulk properties-as well as surface morphologies-present a strong dependence on growth parameters, mainly the V/III ratio. Our results indicate the importance of surface diffusion and, particularly, surface reconstruction for these processes. Most importantly from the application point of view, we show that the compositional modulation is not necessarily coupled to the surface instabilities, so that smooth InGaP films with periodic compositional variation could be obtained. This opens a new route for the generation of templates for quantum dot positioning and three-dimensional arrays of nanostructures FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FINANCIADORA DE ESTUDOS E PROJETOS - FINEP Aberto

Agradecimentos: One of the authors (L.N.) acknowledges scholarship from CNPq. This work was supported by FAPESP and CNPq. HRTEM and GIXD measurements were performed at LME and XRD-2 station, respectively, at the National Laboratory of Synchrotron Light (LNLS, Brazil) Abstract: The authors have investigated strain relaxation in InAs/InGaAs/InP nanowires (NW's). Transmission electron microscopy images show an additional stress field attributed to compositional modulation in the ternary layer, which disrupts NW formation and drives Ga interdiffusion into InAs, according to grazing incidence x-Ray diffraction under anomalous scattering conditions. The strain profile along the NW, however, is not significantly affected when interdiffusion is considered. Results show that the InAs NW energetic stability is preserved with the introduction of ternary buffer layer in the structure CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Orientadores: Mônica Alonso Cotta, Peter Alexander Bleinroth Schulz Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Neste trabalho caracterizamos as propriedades elétricas de nanoestruturas semicondutoras de InAs/InP, principalmente quantum dots e quantum wires, obtidas pelo modo de crescimento Stranski-Krastanov com epitaxia por feixe químico (CBE). Medidas de topografia, de condutância elétrica e corrente-voltagem com resolução espacial foram realizadas nas estruturas crescidas utilizando microscopia de força atômica em modo condutivo (C-AFM) com ponta metalizada. Estruturas tipo mesa foram processadas nas amostras usadas em C-AFM e medidas elétricas a temperaturas mais baixas que 273 K foram adquiridas. Transporte por emissão termiônica tridimensional (não-homogêneo) foi observado entre a ponta condutora e as nanoestruturas de InAs. Isso sugere que as vizinhanças da nanoestrutura, formada pela wetting layer (WL), alteram a configuração da altura da barreira, tornando-a dependente da voltagem aplicada na junção metal-semicondutor. Por outro lado, a voltagem de limiar, definida como a voltagem necessária para obter a menor corrente elétrica detetável, varia com o tamanho e forma da nanoestrutura; ela está relacionada com o estado eletrônico da nanoestrutura e também com o gap eletrônico do semicondutor, que é menor nas nanoestruturas maiores. Condução elétrica por hopping e ruído telegráfico aleatório (RTN) foram observados a baixas temperaturas nos dispositivos fabricados via e-beam com dezenas ou centenas de nanoestruturas de InAs/InP. O transporte tipo hopping de Éfros-Shklovskii ocorre a temperaturas mais altas (> 70 K) e polarizações baixas onde a densidade de portadores no dispositivo é baixa e a interação coulombiana forte. Com o aumento da polarização o hopping muda para intervalo variável de Mott em sistemas 2D, e correlacionado com a dimensionalidade da WL ¿o canal de condução. O RTN aparece em temperaturas mais baixas (< 40 K) mas somente nos dispositivos contendo nanoestruturas que permitem o aprisionamento de portadores. Simulações numéricas usando um modelo heurístico mostraram que poucas nanoestruturas podem alterar o transporte elétrico num ensemble com centenas delas Abstract: In this work we characterized the electrical properties of InAs/InP semiconductor nanostructures, mainly quantum dots e quantum wires, obtained by Stranski-Krastanov growth mode using chemical beam epitaxy (CBE). Topography, electrical conductance, and current-voltage measurements with spatial resolution were performed on the grown structures using atomic force microscopy in conductive mode (C-AFM) with metalized tip. Mesa-like structures were processed on the samples used in C-AFM; electrical measurements at temperatures lower than 273 K were then acquired. Three-dimensional thermionic emission (non-homogeneous) transport was observed between the conductive tip and the InAs nanostructures. This suggests that the nanostructure neighborhood, formed by the wetting layer (WL), changes the barrier height configuration and makes it dependent on the voltage applied to the metal-semiconductor junction. On the other hand, the threshold voltage, defined as the voltage necessary to detect the lowest current level, varies with nanostructure size and shape; it is related to the nanostructure electronic state and also to the semiconductor electronic gap that is smaller for the larger nanostructures. Electrical conductance via hopping and random telegraphic noise (RTN) were observed at low temperatures on the devices fabricated via e-beam with dozens or hundreds of InAs/InP nanostructures. The Éfros-Shklovskii hopping transport occurs at higher temperatures (> 70 K) and low polarizations where the device carrier density is low and the coulombian interaction is strong. Increasing the polarization the hopping changes to the Mott variable range on 2D system, which correlates to the WL dimensionality ¿the conduction channel. The RTN appears in low temperatures (< 40 K) but only in those devices with nanostructures that allow carrier trapping. Numerical simulations using a heuristic model showed that few nanostructures can change the electrical transport in an ensemble with hundreds of them Doutorado Física Doutor em Ciências FAPESP 01/13463-1

Orientador: Mônica Alonso Cotta Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Neste trabalho estudamos os mecanismos de crescimento durante a epitaxia por feixe químico de nanoestruturas III-V baseadas no sistema InAs/InP. Particularmente, foram estudados nanofios e ilhas de InAs sobre uma camada buffer InP(001) e nanofios de InAs sobre uma matriz de InGaAs/InP (com mesmo parâmetro de rede). Apresentaremos, nesta tese, as diferenças e similaridades destes sistemas quanto a condições de crescimento, distribuição de tamanho, forma e os efeitos de volume da camada de InGaAs sobre as nanoestruturas de InAs quando comparadas ao sistema InAs/InP. Nossa escolha do InGaAs/InP como camada buffer para a nucleação dos fios de InAs, foi feita porque facilitaria a utilização deste sistema em diversas aplicações, proporcionando maior flexibilidade no desenho dos dispositivos. Por outro lado, este material abre a possibilidade de controlar as características das nanoestruturas através das propriedades de bulk e superficiais da liga ternária InGaAs. Além disso, ligas ternárias podem exibir efeitos de volume que afetam suas propriedades superficiais. Estes fenômenos podem afetar a nucleação dos fios quânticos e por isso foram objeto de nosso estudo. Para isso utilizamos e correlacionamos medidas in situ de difração de elétrons de alta energia (RHEED), microscopia de força atômica (AFM) e eletrônica de transmissão (TEM), com os resultados obtidos por difração de raios X com incidência rasante (GIXD). Verificamos, deste modo, tanto a influência das condições de crescimento, como o comportamento da relaxação da energia elástica nas nanoestruturas. Com todos estes resultados mostramos como acontece a evolução da deformação nos nanofios e pontos quânticos de InAs/InP e como acontecem as transições de forma entre estes dois tipos de nanoestruturas, em função das condições de crescimento e tipo de superfície do substrato utilizado. Mostramos, também que a introdução de um composto ternário (InGaAs) entre o InAs e o InP não afeta significativamente a forma e tamanho das nanoestruturas quando comparadas ao caso InAs/InP. Em particular, a interdifusão gerada por variações locais da composição na camada buffer em nanofios de InAs pode ser minimizada através de mudanças nas condições de crescimento do InGaAs Abstract: In this work we study the growth mechanisms of III-V nanostructures by chemical beam epitaxy (CBE) based on the InAs/InP materials system. Particularly, nanowires and nanodots of InAs on InP (001) and InAs nanowires on InGaAs/InP (lattice matched) buffer layers were studied. The differences and similarities of these systems are presented in this text, as a function of growth conditions, size distribution, as well as the bulk effects of the InGaAs layer on InAs nanostructures when compared to the InAs/InP system. Our choice of InGaAs/InP buffer layer for InAs nanowire nucleation was due to the possible use of this system in many applications, providing greater flexibility in device design. Furthermore, this material opens up the possibility of controlling nanostructures characteristics through bulk and surface properties of the InGaAs ternary alloy. In other hand, ternary alloys may present volume effects that affect their surface properties. These phenomena can affect quantum wires nucleation and thus became one of the subjects of our study. With these goals in mind, we have correlated in situ high-energy electrons diffraction (RHEED) measurements, atomic force microscopy (AFM) and transmission electron microscopy (TEM) images with the results obtained by grazing incidence X-ray diffraction (GIXD). We report here the influence of the growth conditions on nanostructure shape as well as the behavior of elastic energy relaxation within the nanostructures. Our results show how the evolution of deformation within InAs/InP nanowires and quantum dots occur and how the shape transition between these two types of nanostructures depend on the growth conditions and the substrate surface type used. We also show that the introduction of a ternary compound (InGaAs) between InAs and InP does not significantly affect the shape and size of nanostructures as compared to the InAs / InP case. In particular, the interdifusion generated in InAs nanowires by local variations in the buffer layer composition can be minimized through changes in InGaAs growth conditions Doutorado Estrutura de Líquidos e Sólidos; Cristalografia Doutor em Ciências

Orientador: Mônica Alonso Cotta Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: Os processos cinéticos - difusão e adsorção - responsáveis pela formação de estruturas superficiais na interface sólido-vapor durante a epitaxia de filmes finos cristalinos foram estudados usando o método Monte Carlo Cinético. O crescimento epitaxial foi simulado computacionalmente baseando-se no modelo Solid-on-Solid (SOS). Supõe-se que o cristal possui uma estrutura cúbica simples e que a dinâmica do crescimento pode ser descrita por átomos de apenas uma espécie. A adsorção segue uma taxa constante enquanto que o processo de difusão dos átomos na superfície, associado ao comportamento de osciladores harmônicos bidimensionais, obedece uma taxa tipo Arrhenius. A simulação da evolução da superfície do filme crescido permitiu observar a transição entre modos de crescimento durante a variação da temperatura de crescimento. Com a inclusão da barreira Schwoebel ao modelo verificou-se a formação e evolução de estruturas de formato piramidal. Diferentes morfologias foram obtidas quando diferentes origens de anisotropia foram consideradas. Estudamos detalhadamente a influência de um caso particular de substrato rugoso na evolução dos filmes. Esse estudo possibilitou tanto a reprodução qualitativa dos principais aspectos de resultados experimentais de homoepitaxia de GaA realizada por epitaxia de feixe químico como a con.rmação da existência de uma barreira Schwoebel desprezível para esse sistema Abstract: The kinetic processes - diÿusion and adsorption - responsible by the formation of surface structures at the solid - vapour interface during the epitaxy of crystaline thin films were studied using the Kinetic Monte Carlo method. The computational simulation of epitaxial growth was based on the Solid-on-Solid (SOS) model. A simple cubic structure was used for the descripton of the crystal and the growth dynamics was described by one-specie atoms only. A constant rate describes the adsorption while the difusion process of the atoms on the surface, associated to the behavior of bidimensional harmonic oscillators, obeys an Arrhenius rate. The simulation of the surface evolution of the grown film was able to reproduce the transition between growth modes during with the change of the growth temperature. The formation and evolution of pyramidlike structures were observed when the Schwoebel barrier was included in the model. Different kinds of morphologies were achieved when different origins for anisotropy were considered. We have studied in detail the influence of a particular case of rough substrates on the film evolution. This study qualitatively reproduced the main aspects of experimental results on GaAs homoepitaxy by chemical beam epitaxy and confirmed the existence of a negligible Schwoebel barrier for this system Mestrado Física Mestre em Física

Orientador: Mônica Alonso Cotta Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: Este trabalho teve como objetivo implementar novas técnicas de microscopia por varredura com ponta de prova no equipamento existente no LPD/DFA/UNICAMP e aplicá-las ao estudo de propriedades elétricas de nanoestruturas semicondutoras. Em particular, foi necessário projetar, construir e implementar no microscópio, um circuito eletrônico de medição de corrente com alta sensibilidade para realizar medidas de condutividade local com microscopia por força atômica, utilizando uma ponta condutora. Com a adição de uma placa de aquisição de dados, foi possível obter também medidas de corrente-voltagem com resolução espacial (espectroscopia I'V). As técnicas implementadas foram primeiramente aplicadas em diferentes materiais no sentido de testar seu funcionamento, resolução e limites de utilização. Posteriormente aplicamos as técnicas de caracterização elétrica a filmes semicondutores crescidos por epitaxia de feixe químico, com particular interesse em filmes tensionados que originam nanoestruturas. O modo de força eletrostática foi utilizado para medidas do potencial de superfície (diferença entre as funções trabalho de dois materiais), com a finalidade de determinar a posição do nível de Fermi das diferentes amostras estudadas. Neste caso, a placa de aquisição de dados foi utilizada para fornecer diretamente o potencial de superfície, semelhante à técnica Kelvin-Probe. Embora a técnica não tenha mostrado resolução espacial para identificação das nanoestruturas na superfície da amostra, puderam ser observadas diferenças entre as várias amostras analisadas, interpretadas como resultado da presença do filme tensionado. Medidas de corrente e espectroscopia I'V, em amostras de InAs/InP, mostraram que a característica elétrica do contato entre a ponta metalizada e um dot é do tipo Schottky, devido à oxidação causada pela exposição ao ar. Variações de corrente sobre diferentes regiões de um mesmo dot são atribuídas a efeitos de convolução ponta-amostra. Utilizando o microscópio de força atômica como ferramenta para nanolitografia, foram desenvolvidos os processos iniciais para produção de dispositivos com as nanoestruturas crescidas. Isso permitirá que sejam realizadas medidas de transporte elétrico entre as nanoestruturas, com temperaturas mais baixas que a ambiente Abstract: In this work new scanning probe techniques were implemented to the existing atomic force microscope at LPD/DFA/UNICAMP and used to study the electrical properties of semiconductor nanostructures. To achieve this goal, it was necessary to design, build and set up an eletronic circuit able to measure currents with high sensitivity, for local conductance measurements with the atomic force microscope using conducting tips. With the addition of a data acquisition board, spatially-resolved current-voltage measurements (I'V spectroscopy) were obtained. The new techniques were first used with different materials in order to test their functioning, limits and resolution. After that, the electrical characterization techniques were used to study semiconductor samples grown by chemical beam epitaxy, with particular interest in strained films with self-assembled nanostructures. Electrostatic force microscopy was used for surface potential (difference in the work function of two different materials) measurements in order to determine the Fermi level energy of our samples. In this case the data acquisition board was used to directly provide the surface potential, similarly to the Kelvin-Probe technique. Although our results could not spatially resolve the surface nanostructures in our samples, different surface potential values were measured for the different samples, and were interpreted as a result of the presence of the strained film. Current measurements as well as I'V spectroscopy for InAs/InP samples have shown a Schottky-type contact for the metalized tip and dot, due to the oxidation of the sample surface caused by exposure to air. Current variations over different regions of the same dot were attributed to the tip-sample convolution. Using the atomic force microscope as a nanolithography tool, we have developed the initial processing steps to produce devices with the epitaxial nanostructures. This will allow electrical transport experiments at temperatures lower than 300K Mestrado Física Mestre em Física

Orientador: Mônica Alonso Cotta Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Nesta tese investigamos processos de adesão da Xylella fastidiosa, bactéria gram-negativa, fitopatógena, que forma biofilmes no xilema de plantas. O trabalho teve como objetivos entender alguns aspectos do processo de adesão bacteriana e do mecanismo de transporte de células e biofilmes em sistemas que simulam os vasos do xilema. Consideramos em particular as estratégias utilizadas pela X.fastidiosa para aderir à superfície, dentre elas, a secreção de substâncias poliméricas extracelulares (EPS), a presença de adesinas fimbriais (pili) e afimbriais (XadA1) e moléculas sinalizadoras de detecção de quórum (relacionadas à formação de agregados). Como ponto de partida quantificamos as propriedades elásticas do sistema composto pelo EPS e células bacterianas, em diferentes tempos de cultivo bacteriano. Para isso utilizamos medidas de espectroscopia de força e Raman confocal durante os estágios iniciais de adesão celular e formação de agregados. Mostramos que a rigidez do sistema célula/EPS diminui progressivamente com o aumento do tempo de crescimento bacteriano. Verificamos que existe uma mudança no valor de rigidez em diferentes partes da célula, região polar e corpo bacteriano; os menores valores de rigidez encontrados no polo sugerem uma resposta mecânica mais flexível nesta região, associada com o ponto de adesão inicial da célula à superfície. No estudo de adesão e mobilidade da X.fastidiosa, utilizamos dispositivos microfluídicos modificados quimicamente, via funcionalização de superfície (em microcanais Polidimetilsiloxano/vidro) e via introdução de molécula de detecção de quórum (em microcanais impressos em poliácido láctico), para tornar o ambiente mais próximo ao do xilema da planta. Foram feitas funcionalizações de superfície com uma celulose sintética, simulando a composição química dos vasos do xilema (majoritariamente composto por celulose), e com a adesina XadA1, e observamos os efeitos sobre a adesão, crescimento e mobilidade celular. Verificamos que a adesina XadA1 aumenta a densidade bacteriana se comparada às demais superficies, além de aumentar a força de adesão bacteriana à superfície. Quanto a inserção de molécula sinalizadora, observamos que a presença destas moléculas no cultivo bacteriano aumenta a densidade celular e altera a forma de pequenos agregados Abstract: In this thesis we investigated the adhesion processes of Xylella fastidiosa, a gram-negative, phytopathogenic bacterium that forms biofilms in the xylem of plants. The objective of this work was the understanding of several aspects of the bacterial adhesion process, as well as the mechanism of cell and biofilm transport in systems that simulate xylem vessels. In particular, we considered the strategies used by X.fastidiosa to adhere to a surface; among them, the secretion of extracellular polymeric substances (EPS), the presence of fimbrial (pili) and afimbrial (XadA1) adhesins and quorum detection molecules (related to cluster formation). As a starting point we quantified the elastic properties of the system composed of EPS and bacterial cells, at different times of bacterial culture. For this purpose, we used force spectroscopy and confocal Raman measurements during the initial stages of cell adhesion and cluster formation. We have shown that stiffness decreases progressively with increasing bacterial growth time. We observed that stiffness values varied along different parts of the cell, polar region and bacterial body. The lower stiffness values found at the pole suggest a more flexible mechanical response in this region, associated with the initial adhesion point of the cell to the surface. For the investigation on X.fastidiosa adhesion and mobility, we used chemically modified microfluidic devices via surface functionalization (in Polydimethylsiloxane / glass microchannels) and via the introduction of a quorum detection molecule (in microchannels printed on polylactic acid) to make the environment more closely resemble the plant xylem. Surface functionalizations were performed with a synthetic cellulose, simulating the chemical composition of xylem vessels (mainly composed of cellulose), and the XadA1 adhesin, and we observed the effects on cell adhesion, growth and mobility. Our results showed that immobilized XadA1 increased the bacterial density when compared to other surfaces studied; furthermore, it increased the bacterial adhesion force to the surface. Regarding the addition of the signaling molecules, we observed that their presence in the bacterial culture increases cell density and changes the shape of small clusters Doutorado Física Doutora em Ciências FAPESP 2010/51748-7 CNPQ 479486/2012-3 CAPES

Orientador: Mônica Alonso Cotta Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Neste trabalho estudamos características físico-químicas nos diferentes estágios de formação de biofilmes, principalmente no estágio inicial da adesão de bactérias planctônicas em superfícies. Usamos como modelo a bactéria fitopatogênica Xylella fastidiosa, que vive exclusivamente no xilema de diversas plantas lenhosas e é transmitido por diferentes insetos da ordem Hemíptera. As amostras analisadas neste estudo foram todas cultivadas sobre superfícies inorgânicas e após diferentes tempos de cultivo foram lavadas e secas antes de serem analisadas. Para estudar o processo integral de formação de biofilmes, examinamos amostras cultivadas sobre superfícies de vidro e Silício recoberto com ouro, em um meio de cultura complexo, chamado Periwinkle wilt. Através de técnicas como citoquímica, imunomarcação, microscopia e espectroscopia, analisamos os elementos produzidos pelas bactérias ou presentes na membrana celular durante cada estágio da formação de biofilmes. Conseguimos identificar espaço-temporalmente a aparição de pili, vesículas e três tipos diferentes de sustâncias poliméricas extracelulares, assim como algumas moléculas específicas que compõem estes elementos. Posteriormente, focalizamos nossos esforços no processo de adesão inicial em superfícies. Estudaram-se os três principais componentes envolvidos neste processo: adesinas, meio líquido e superfície. Primeiramente, se analisaram amostras de bactérias aderidas em superfícies de Silício. Nestas amostras aplicamos diferentes reagentes com a finalidade de investigar que tipo de ligação química está presente na interface adesina-superfície. Determinou-se que uma das ligações presentes nesta interface é a ligação glicosídica e que provavelmente está relacionada com as moléculas de lipopolissacarídeo localizadas na membrana bacteriana. A complexidade do meio de cultura fez que o estudo dos seus componentes fosse o elemento mais complicado de analisar. Inicialmente, deveram-se procurar as condições mínimas nas quais as bactérias sobrevivem, porém não conseguem aderir em superfícies. Assim, um meio de cultura complexo e definido, chamado Xylella fastidiosa Medium, foi modificado eliminando as componentes não relacionadas diretamente com a adesão bacteriana. Logo, adicionamos sistematicamente diferentes tipos de moléculas e/ou íons no meio de cultura simplificado identificando as condições que favorecem o processo de adesão. Encontramos uma dependência da adesão bacteriana com o pH do meio e a presença de cátions bivalentes com baixa energia de ionização. Como último parâmetro, estudamos a participação da superfície neste processo. Neste caso, além das superfícies de Silício, também usamos superfícies de Fosfeto de Índio para estudar o processo de adesão como função do pH do meio de cultura. A adesão nestas superfícies só apresentou diferenças significativas em um intervalo específico de pH. Analisando o conjunto de evidências obtidas em nossos experimentos, conseguiu-se formular um modelo que descreve este fenômeno tendo em conta todos os parâmetros estudados. Descreve-se o processo de adesão como a interação entre concentrações de duas espécies de moléculas diferentes alusivas à adesina e à superfície. Sugerimos que o processo de adesão pode ser tratado como um mecanismo puramente físico-químico e não biológico, razão pela qual nosso modelo poderia ser em teoria extrapolado a qualquer tipo de superfície e qualquer tipo de bactéria Abstract: In this work we study physico-chemical characteristics in the different stages of biofilm formation, particularly in the early stages of adhesion of planktonic bacteria to surfaces. We use as model the phytopathogenic bacterium Xylella fastidiosa, which lives exclusively in the xylem of several woody plants and is transmitted by different insects of the order Hemiptera. The samples analyzed in this study were all grown on inorganic surfaces and after different culture times were washed and dried before being analyzed. To study the entire biofilm formation process, we examined samples grown on glass and silicon covered with gold surfaces in a complex culture medium called Periwinkle wilt. Through techniques such as cytochemistry, immunostaining, microscopy and spectroscopy, we analyze the elements produced by the bacteria or present in the cell membrane during each stage of biofilm formation. We have been able to identify space-temporally the appearance of pili, vesicles and three different types of extracellular polymeric substances, as well as some specific molecules that compose these elements. Subsequently, we focused our efforts on the initial cell binding process on surfaces. The three main components that intervene in this process were studied: adhesins, liquid medium and surface. First, samples of bacteria adhered to silicon surfaces were analyzed. In these samples, we applied different reagents to investigate the type of chemical bond present at the adhesin-surface interface. It has been determined that one of the bonds present at this interface is the glycosidic bond, which is probably related to the lipopolysaccharide molecules located in the bacterial membrane. The complexity of the culture medium made the study of its components the most complicated element to analyze. Initially, it was necessary to look for the minimum conditions in which the bacteria survive, but they cannot adhere to surfaces. Thus, a complex and defined culture medium, called Xylella fastidiosa Medium, was modified eliminating components not directly related to bacterial adhesion. Then, we systematically add different types of molecules and / or ions in the simplified culture medium, identifying the conditions that favor the adhesion process. We found a dependence of bacterial adhesion with the pH of the medium and the presence of bivalent cations with low ionization energy. As a final parameter, we studied the participation of the surface in this process. In this case, in addition to the Silicon surfaces, we also used Indium Phosphide surfaces to study the adhesion process as a function of the pH of the culture medium. Adhesion on these surfaces only showed significant differences over a specific pH range. Analyzing the set of evidences obtained in our experiments, we were able to formulate a model that describes this phenomenon taking into account all the parameters studied. The adhesion process is described as the interaction between concentrations of two different species of molecules alluding to adhesin and to the surface. We suggest that the adhesion process can be treated as a purely physico-chemical and non-biological mechanism, so that our model could in theory be extrapolated to any type of surface and any type of bacteria Doutorado Física Doutor em Ciências CAPES 1060584 FAPESP 2010/51748-7 CNPQ 479486/2012-3

Orientadores: Luiz Fernando Zagonel, Mônica Alonso Cotta Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Neste trabalho, estudamos a dinâmica de crescimento de nanofios de GaP crescidos pelo método VLS (Vapor-Líquido-Sólido) via Epitaxia por Feixe Químico (CBE), usando nanopartículas catalisadoras de ouro. Investigando o efeito da temperatura na dinâmica de crescimento de nanofios de GaP encontramos uma grande variedade de nanofios em cada amostra, caracterizadas por diferentes direções de crescimento e/ou morfologias, apresentando sempre uma população dominante. Com o aumento da temperatura (510°C) observamos uma transição drástica na morfologia da população dominante, de nanofios típicos para uma nova e inesperada morfologia assimétrica. Mostramos ainda que modificando o tamanho da nanopartícula catalisadora de 5nm para 20nm os nanofios assimétricos ainda são favorecidos a alta temperatura. Procurando compreender o mecanismo de formação dos nanofios assimétricos, mostramos que estas estruturas cristalizam-se na fase WZ, com baixa densidade de defeitos, comparadas às outras amostras. Além disso, mostramos que a assimetria destes nanofios não é oriunda de diferenças de polaridade nas facetas laterais ou formação de defeitos cristalográficos que pudessem modificar a dinâmica de crescimento de modo a levar à morfologia assimétrica. Desta forma, propomos um cenário de crescimento simplificado, no qual a estrutura assimétrica é formada pela combinação do crescimento de nanofios ordinários, via VLS, junto com estruturas que crescem livre de catalizador via mecanismo VS (Vapor-Sólido), estas duas estruturas então se juntam, transferindo material e dando lugar a facetas de menor energia, resultando na formação da estrutura assimétrica. Por fim, medidas de fotoluminescência mostram a emissão característica no verde do GaP WZ para os nanofios assimétricos, mesmo com a estrutura não estando passivada, confirmando a boa qualidade cristalina das nossas amostras Abstract: In this work, we study the growth dynamics of GaP nanowires grown by VLS (Vapor-Liquid-Solid) method via Chemical Beam Epitaxy (CBE) using gold nanoparticles as catalyst. Investigating the effect of temperature on the growth dynamics of GaP nanowires we find a wide variety of nanowires in each sample, characterized by different growth directions and/or morphologies, always having a dominant population. With increasing temperature (510°C), we observed a dramatic transition in the morphology of the dominant population of typical nanowires to a new and unexpected asymmetric morphology. We also show that modifying the size of the catalyst nanoparticle from 5nm to 20mn the asymmetric nanowires are still favored at high temperature. Looking forward to understand the mechanism of formation of the asymmetric nanowires, we show that these structures crystallize in the WZ phase with low defect density when compared to the other samples. Furthermore, we show that the asymmetry of these nanowires is not derived from differences in polarity in side facets or the formation of crystallographic defects which might modify the growth dynamics so as to bring the asymmetric morphology. Thus, we propose a simplified growth scenario, in which the asymmetric structure is formed by growth combination of ordinary nanowires via VLS, along with structures that grow catalyst-free via VS (vapor-solid) mechanism, these two structures joined and by transferring materials facets with lower energy facets appear, resulting in the formation of asymmetrical structure. Finally, photoluminescence measurements show the characteristic emission in the green of WZ GaP for asymmetric nanowires, even with no passivation, which confirms the good crystalline quality of our samples Mestrado Física Mestre em Física FAEPEX CNPQ CAPES FAPESP

Orientadora: Mônica Alonso Cotta Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Este trabalho apresenta resultados de nossa investigação sobre as propriedades elétricas do biossensor do tipo transistor de efeito de campo (FET, do inglês Field Effect Transistor) baseado em fosfeto de índio (InP). A estrutura deste biossensor consiste em um filme fino de InP do tipo-n crescido por Epitaxia de Feixe Químico (CBE, do inglês Chemical Beam Epitaxy) sobre um substrato de InP semi-isolante. No nosso biosensor, o contato da porta foi substituído por uma camada de biomoléculas carregadas de interesse para a detecção, funcionalizadas na camada de óxido do InP. O campo elétrico associado a estas biomoléculas pode modular o canal de condução. O sistema de interação específica utilizado foi a hibridização de fitas de ssDNA (single stranded DNA) complementares, onde os oligonucleotídeos receptores (probe) ssDNA foram imobilizados covalentemente na superfície da amostra. Este procedimento foi realizado através da oxidação com plasma de O2, seguida da funcionalização utilizando etanolamina e polietileno glicol (PEG), que serve como linker para a imobilização de receptores na superfície. As medidas elétricas de detecção foram feitas com as moléculas de target diluídas em buffer TRIS. A hibridização do DNA provoca um aumento na densidade de cargas na superfície, que consequentemente aumenta a largura da região de depleção no semicondutor, variando a resistência medida. A resposta do biossensor corresponde à variação da resistência em função da concentração de target. O biossensor apresentou sensibilidade para medidas de concentrações entre 10 pM e 30 pM, onde ocorre a saturação, e o tempo de resposta, no qual encontramos a estabilização do sinal medido, foi de aproximadamente 20 min. Variando a concentração de portadores e a espessura da camada semicondutora, verificamos alterações no limite de saturação (até ?M) e na sensibilidade do dispositivo. O controle destas propriedades, porém, mostrou-se limitado devido à variações na dopagem residual do semicondutor, e por isso discutimos aqui alternativas à geometria do dispositivo. Analisamos também a camada funcionalizada através de medidas de topografia e potencial de superfície usando métodos de microscopia de varredura por sonda (SPM, do inglês Scanning Probe Microscopy). Pudemos identificar a variação no potencial de superfície associada à imobilização do PEG e do DNA probe, mas não obtivemos resolução para o DNA target. Esta técnica permitiu porém verificar a estratificação de quatro níveis de potencial de superfície, no caso onde a funcionalização resultou em camadas mais espessas do que os valores típicos (~2 nm de espessura), em pequenas áreas do semicondutor Abstract: This dissertation presents our results for the electrical properties investigation of Indium Phosphide (InP) based Field Effect Transistor (FET) biosensor. The structure of this biosensor consists of a thin n-type InP film grown by Chemical Beam Epitaxy (CBE) on a semi-insulating InP substrate. In our biosensor, the gate contact has been replaced by charged biomolecules of interest for detection, functionalized to the InP oxide layer. The electric field associated with these biomolecules provides the conduction channel modulation. The specific interaction system used here was the hybridization of single stranded-DNA (ssDNA) complementary oligonucleotides, for which the ssDNA receivers (probes) were covalently immobilized on the sample surface. The functionalization was carried out by oxidation with O2 plasma, followed by grafting biomolecules using ethanolamine and polyethylene glycol (PEG), which act as a linker for immobilizing the receptors on the surface. Electrical detection measurements were made with the target molecules diluted in TRIS buffer. DNA hybridization causes an increase in the surface charge density; consequently the semiconductor depletion width increases, affecting the measured resistance. The biosensor response function corresponds to the resistance variation as a function of target concentration. Our biosensor showed measured sensitivity to concentrations between 10 pM and 30 pM, for which signal saturation occurs. The response time, for which the measured signal stabilization was observed, was approximately 20 min. By varying the carrier concentration and the thickness of the semiconductor layer, we observed changes in the saturation limit (up ?M) and device sensitivity. The control of these properties, however, is limited due to variations in the residual doping of the semiconductor. Therefore we discuss here alternative device geometries. We also analyzed the functionalized layer by topography and surface potential measurements obtained using scanning probe microscopy (SPM) methods. We were able to identify the change in surface potential associated with the immobilization of PEG and probe DNA, but not for the target DNA. These techniques have however shown four surface potential levels in the case when the functionalization resulted in non-uniform layers, thicker than the typical values (~ 2 nm), in small areas of the semiconductor Mestrado Física Mestra em Física CNPQ 165741/2014-7 FAPESP CAPES