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Multifunctional micro- and nanoparticles have potential uses in advanced detection methods, such as the combined separation and detection of biomolecules. Combining multiple tasks is possible but requires the specific tailoring of these particles during synthesis or further functionalization. Here, we synthesized nanostructured gold shells on magnetic particle cores and demonstrated the use of them in surface-enhanced Raman scattering (SERS). To grow the gold shells, gold seeds were bound to silica-coated iron oxide aggregate particles. We explored different functional groups on the surface to achieve different interactions with gold seeds. Then, we used an aqueous cetyltrimethylammonium bromide (CTAB)-based strategy to grow the seeds into spikes. We investigated the influence of the surface chemistry on seed attachment and on further growth of spikes. We also explored different experimental conditions to achieve either spiky or bumpy plasmonic structures on the particles. We demonstrated that the particles showed SERS enhancement of a model Raman probe molecule, 2-mercaptopyrimidine, on the order of 10 4 . We also investigated the impact of gold shell morphology-spiky or bumpy-on SERS enhancements and on particle stability over time. We found that spiky shells lead to greater enhancements, however their high aspect ratio structures are less stable and morphological changes occur more quickly than observed with bumpy shells.

Combined separation and detection of biomolecules has the potential to speed up and improve the sensitivity of disease detection, environmental testing, and biomolecular analysis. In this work, we synthesized magnetic particles coated with spiky nanostructured gold shells and used them to magnetically separate out and detect oligonucleotides using SERS. The distance dependence of the SERS signal was then harnessed to detect DNA hybridization using a Raman label bound to a hairpin probe. The distance of the Raman label from the surface increased upon complementary DNA hybridization, leading to a decrease in signal intensity. This work demonstrates the use of the particles for combined separation and detection of oligonucleotides without the use of an extrinsic tag or secondary hybridization step., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Adsorption of the Glycine-Proline (Gly-Pro) dipeptide has been investigated using surface science complementary techniques on Au(110) and Ag(110), showing some interesting differences both in the chemical form and surface organization of the adsorbed peptide. On Au(110), Gly-Pro mainly adsorbs in neutral form (COOH/NH 2 ), at low coverage or for a short interaction time; the surface species become zwitterionic at a higher coverage or longer interaction time. These changes are accompanied by a complete reorganization of the molecules at the surface. On Ag(110), only anionic molecules (COO - /NH 2 ) were detected on the surface and only one type of arrangement was observed. These results will be compared to some previously obtained on Cu(110), thus providing a unique comparison of the adsorption of the same di-peptide on three different metal surfaces; the great influence of the substrate on both the chemical form and the arrangement of adsorbed di-peptides was made clear.

Sophorolipids are bioderived glycolipids displaying interesting antimicrobial properties. We show that they can be used to develop biocidal monolayers against Listeria ivanovii, a Gram-positive bacterium. The present work points out the dependence between the surface density and the antibacterial activity of grafted sophorolipids. It also emphasizes the broad spectrum of activity of these coatings, demonstrating their potential against both Gram-positive strains (Enteroccocus faecalis, Staphylococcus epidermidis, Streptococcus pyogenes) and Gram-negative strains (Escherichia coli, Pseudomonas aeruginosa and Salmonella typhymurium). After exposure to sophorolipids grafted onto gold, all these bacterial strains show a significant reduction in viability resulting from membrane damage as evidenced by fluorescent labelling and SEM-FEG analysis., (Copyright © 2017 Elsevier B.V. All rights reserved.)

By changing the ultrahigh vacuum (UHV) deposition method, classical sublimation versus electrospray ionization, one can tune the chemistry of a chiral dipeptide molecule (Gly-Pro, GP), when adsorbed on a Cu(110) surface, from anionic to zwitterionic. This chemical shift will influence the adsorption mode of the dipeptide, either in a three-point fashion in the case of anionic GP molecules with a strong interaction among the copper surface, both O atoms of the carboxylate moiety, and the nitrogen atoms, or in the case of zwitterions GP, the adsorption mode relies on the sole interaction of one carboxylate oxygen atom. These different anchoring modes strongly modify the expression of surface 2D chirality and the supramolecular assemblies with two very distinct unit cells.

Amino acids and peptides are often used as "model" segments of proteins for studying their behavior in various types of environments, and/or elaborating functional surfaces. Indeed, though the protein behavior is much more complex than that of their isolated segments, knowledge of the binding mode as well as of the chemical structure of peptides on metal or oxide surfaces is a significant step toward the control of materials in a biological environment. Such knowledge has considerably increased in the past few years, thanks to the combination of advanced characterization techniques and of modeling methods. Investigations of biomolecule-surface interactions in water/solvent environments are quite numerous, but only in a few cases is it possible to reach an understanding of the molecule-(water)-surface interaction with a level of detail comparable to that of the UHV studies. This contribution aims at reviewing the recent data describing the amino acid and peptide interaction with metal or oxide surfaces in the presence of water.

We report a simple and original method to synthesize gold nanoparticles in which a fungal protein, the hydrophobin Vmh2 from Pleurotus ostreatus and dicarboxylic acid-terminated polyethylene-glycol (PEG) has been used as additional components in a one step process, leading to hybrid protein-metal nanoparticles (NPs). The nanoparticles have been characterized by ultra-violet/visible, infrared and X-ray photoelectron spectroscopies, dynamic light scattering and also by electron microscopy imaging. The results of these analytical techniques highlight nanometric sized, stable, hybrid complexes of about 12 nm, with outer surface rich in functional chemical groups. Interaction with protein and antibodies has also been exploited., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Adhesion of proteins and bacteria was reduced by a factor close to one order of magnitude, and adhered bacteria were dramatically damaged on copper surfaces by grafting a PEG-modified PMMA-based (polymethyl methacrylate) copolymer together with an antimicrobial peptide. To obtain PEG and a peptide grafted together on the surface, a UV sensitive copolymer (containing PMMA, PEG and a UV sensitive reagent) was primary synthesized and deposited. After selective UV irradiation of this copolymer layer, an antimicrobial peptide, Magainin I, was grafted onto freed-polymer coated-copper surface via a spacer molecule (a mercapto carboxylic acid). The functionalization was characterized at each step by Polarization Modulation Reflection Absorption Infrared Spectroscopy (PM-RAIRS). The antiadhesive properties of the copolymer layer and antibacterial activity of the anchored Magainin I, were individually tested toward adsorption of bovine serum albumin (BSA) proteins, and against Gram positive bacteria, Listeria ivanovii, respectively. The results revealed that adhesion of both proteins and bacteria has been considerably reduced; moreover, the peptide still displays some antimicrobial activity after grafting. This work gives new ideas and perspectives to elaborate complex surface coatings where several agents are needed like for anti-biofilm or sensing applications., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In this paper, we describe the successful construction, characteristics and interaction with proteins of stimuli-responsive thin nanostructured films prepared by layer-by-layer (LbL) sequential assembly of PNIPAM-containing polyelectrolytes and PAH. PAA-b-PNIPAM block copolymers were synthesized in order to benefit from (i) the ionizable properties of PAA, to be involved in the LbL assembly, and (ii) the sensitivity of PNIPAM to temperature stimulus. The impact of parameters related to the structure and size of the macromolecules (their molecular weight and the relative degree of polymerization of PAA and PNIPAM), and the interaction with proteins under physico-chemical stimuli, such as pH and temperature, are carefully investigated. The incorporation of PAA-b-PNIPAM into multilayered films is shown to be successful whatever the block copolymer used, resulting in slightly thicker films than the corresponding (PAA/PAH)n film. Importantly, the protein adsorption studies demonstrate that it is possible to alter the adsorption behavior of proteins on (PAA-b-PNIPAM/PAH)n surfaces by varying the temperature and/or the pH of the medium, which seems to be intimately related to two key factors: (i) the ability of PNIPAM units to undergo conformational changes and (ii) the structural changes of the film made of weak polyelectrolytes. The simplicity of construction of these PNIPAM block copolymer-based LbL coatings on a large range of substrates, combined with their highly tunable features, make them ideal candidates to be employed for various biomedical applications requiring the control of protein adsorption.

Despite the numerous studies on the self-assembled monolayers (SAMs) of alkylthiols on gold, the mechanisms involved, especially the nature and influence of the thiol-gold interface are still under debate. In this work the adsorption of aminothiols on Au(111) surfaces has been studied by using surface IR and X-ray photoelectron spectroscopy (XPS) as well as by density functional theory (DFT) modeling. Two aminothiols were used, cysteamine (CEA) and mercaptoundecylamine (MUAM), which contain two and eleven carbon atoms, respectively. By combining experimental and theoretical methods, it was possible to draw a molecular picture of the thiol-gold interface. The long-chain aminothiol produced better ordered SAMs, but, interestingly, the XPS data showed different sulfur binding environments depending on the alkyl chain length; an additional peak at low binding energy was observed upon CEA adsorption, which indicates the presence of sulfur in a different environment. DFT modeling showed that the positions of the sulfur atoms in the SAMs on gold with similar unit cells [(2√3×2√3)R30°] depended on the length of the alkyl chain. Short-chain alkylthiol SAMs were adsorbed more strongly than long-chain thiol SAMs and were shown to induce surface reconstruction by extracting atoms from the surface, possibly forming adatom/vacancy combinations that lead to the additional XPS peak. In the case of short alkylthiols, the thiol-gold interface governs the layer, CEA adsorbs strongly, and the mechanism is closer to single-molecule adsorption than self-assembly, whereas for long chains, interactions between alkyl chains drive the system to self-assembly, leading to a higher level of SAM organization and restricting the influence of the sulfur-gold interface., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Classical antibacterial surfaces usually involve antiadhesive and/or biocidal strategies. Glycosylated surfaces are usually used to prevent biofilm formation via antiadhesive mechanisms. We report here the first example of a glycosylated surface with biocidal properties created by the covalent grafting of sophorolipids (a sophorose unit linked by a glycosidic bond to an oleic acid) through a self-assembled monolayer (SAM) of short aminothiols on gold (111) surfaces. The biocidal effect of such surfaces on Gram+ bacteria was assessed by a wide combination of techniques including microscopy observations, fluorescent staining, and bacterial growth tests. About 50% of the bacteria are killed via alteration of the cell envelope. In addition, the roles of the sophorose unit and aliphatic chain configuration are highlighted by the lack of activity of substrates modified, respectively, with sophorose-free oleic acid and sophorolipid-derivative having a saturated aliphatic chain. This system demonstrates thus the direct implication of a carbohydrate in the destabilization and disruption of the bacterial cell envelope.

The adsorption of chiral Gly-Pro dipeptide on Cu(110) has been characterized by combining in situ polarization modulation infrared reflection absorption spectroscopy (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS). The chemical state of the dipeptide, and its anchoring points and adsorption geometry, were determined at various coverage values. Gly-Pro molecules are present on Cu(110) in their anionic form (NH2 /COO(-)) and adsorb under a 3-point binding via both oxygen atoms of the carboxylate group and via the nitrogen atom of the amine group. Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) have shown the presence of an extended 2D chiral array, sustained via intermolecular H-bonds interactions. Furthermore, due to the particular shape of the molecule, only one homochiral domain is formed, creating thus a truly chiral surface., (© 2015 Wiley Periodicals, Inc.)

Development of resistant bacteria onto biomaterials is a major problem leading to nosocomial infections. Antimicrobial peptides are good candidates for the generation of antimicrobial surfaces because of their broad-spectrum activity and their original mechanism of action (i.e. rapid lysis of the bacterial membrane) making them less susceptible to the development of bacterial resistance. In this study, we report on the covalent immobilisation of temporin-SHa on a gold surface modified by a thiolated self-assembled monolayer. Temporin-SHa (FLSGIVGMLGKLF amide) is a small hydrophobic and low cationic antimicrobial peptide with potent and very broad-spectrum activity against Gram-positive and Gram-negative bacteria, yeasts and parasites. We have analysed the influence of the binding mode of temporin-SHa on the antibacterial efficiency by using a covalent binding either via the peptide NH2 groups (random grafting of α- and ε-NH2 to the surface) or via its C-terminal end (oriented grafting using the analogue temporin-SHa-COOH). The surface functionalization was characterised by IR spectroscopy (polarisation modulation reflection absorption IR spectroscopy) while antibacterial activity against Listeria ivanovii was assessed by microscopy techniques, such as atomic force microscopy and scanning electron microscopy equipped with a field emission gun. Our results revealed that temporin-SHa retains its antimicrobial activity after covalent grafting. A higher amount of bound temporin-SHa is observed for the C-terminally oriented grafting compared with the random grafting (NH2 groups). Temporin-SHa therefore represents an attractive candidate as antimicrobial coating agent., (Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.)

Controlled immobilization of proteins is crucial in many applications, including biosensors. Allergen biosensing, for example, requires molecular recognition of suitably immobilized proteins by specific antibodies and sensitive measurement of this interaction. Self-assembled monolayers (SAMs), terminated by active functions, and are of great interest for the immobilization of biomolecules. The efficiency of further biorecognition involving molecules immobilized on these surfaces demonstrates an interesting dependence on the chain length and terminal function of the SAM. This motivated us to investigate adsorption of two proteins both known as milk allergens-β-lactoglobulin and apo-transferrin-on amine-terminated SAMs. We varied the chain length by using either short or long chain amine-terminated thiols (cysteamine, CEA, and 11-mercaptoundecylamine, MUAM). We also investigated the influence of the addition of a rigid cross-linker, p-phenylene diisothiocyanate (PDITC), to these amine layers prior to protein adsorption. Protein binding was studied using polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) and atomic force microscopy (AFM) to characterize their amount and dispersion. We found that protein immobilization varies with SAM chain length and is also influenced by the presence of a cross-linker. The presence of a rigid cross-linker favours the binding of proteins on long chain SAMs, while the effect is almost nonexistent on shorter chains. In addition, the presence of the cross-linker induces a better dispersion of the proteins on the surfaces, regardless of the length of the thiols forming the SAMs. The effects of chain length and chemistry of protein binding are discussed., (Copyright © 2014. Published by Elsevier B.V.)

Aromatic self-assembled monolayers (SAMs) can be used as negative tone electron resists in functional surface lithographic fabrication. A dense and resistant molecular network is obtained under electron irradiation through the formation of a cross-linked network. The elementary processes and possible mechanisms involved were investigated through the response of a model aromatic SAM, p-terphenylthiol SAM, to low-energy electron (0-10 eV) irradiation. Energy loss spectra as well as vibrational excitation functions were measured using High Resolution Electron Energy Loss Spectroscopy (HREELS). A resonant electron attachment process was identified around 6 eV through associated enhanced excitation probability of the CH stretching modes ν(CH)(ph) at 378 meV. Electron irradiation at 6 eV was observed to induce a peak around 367 meV in the energy loss spectra, attributed to the formation of sp(3)-hybridized CHx groups within the SAM. This partial loss of aromaticity is interpreted to be the result of resonance formation, which relaxes by reorganization and/or CH bond dissociation mechanisms followed by radical chain reactions. These processes may also account for cross-linking induced by electron irradiation of aromatic SAMs in general.

A combination of XPS, in situ RAIRS, LEED, and STM experiments together with ab initio DFT calculations were used to elucidate the self-assembly properties at the atomic level, and enabled the interpretation of the expression of surface chirality upon adsorption of both enantiomers of methionine on a clean Au(111) surface under UHV conditions. The combination of experimental results, in particular, LEED and STM data with quantum chemical calculations is shown to be a successful setup strategy for addressing this challenge. It was found that the methionine molecular self-assembly consists of the first molecule lying parallel to the gold surface and the second interacting with the first methionine through a 2D H-bond network. The interaction with the gold surface is weak. The stability of the assembly is mainly due to the presence of intermolecular H bonds, resulting in the formation of ziplike dimer rows on the Au(111) surface. The methionine molecules interact with each other via their amino acid functional groups. The assembly shows an asymmetric pattern due to a slightly different orientation of the methionine molecules with respect to the surface. Simulations of the STM image of methionine assemblies were consistent with the experimental STM image. The present study shows another example of Au(111) stabilizing a self-assembled biological layer, which is not chemically perturbed by the surface.

We show in this article that doxorubicin-modified gold nanoparticles (Au NP-DOX) can be used for the post-amplification of the wavelength shift of localized surface plasmon resonance (LSPR) signals after DNA hybridization events. We take advantage of the intercalation properties of DOX with guanine-rich oligonucleotides and the plasmon coupling between surface-linked gold nanostructures and Au NP-DOX in solution to detect in a sensitive manner DNA hybridisation events. Post-treatment of double-stranded DNA with Au NP-DOX resulted in a detection limit of ≈600 pM, several times lower than that without post-incubation (LOD ≈ 40 nM).

As of lately, the demand for developing artificial sensors with improved capabilities for the detection of explosives, toxics or drugs has increased. Ideally, sensor devices should provide high sensitivity and give a response that is specific to a given target molecule without being influenced by possible interfering molecules in the atmosphere. These properties strongly depend on the structure of the chemical compound used as a sensitive material. It is thus crucial to select the right compound and this step would be facilitated with the aid of predictive tools. The present investigations have been focused on a family of functionalized polysiloxane polymers deposited on a QCM device, producing only weak interactions compatible with reversible sensors. The quartz frequency variation at equilibrium has been linked to the partition coefficient that was evaluated using a thermodynamic description of the adsorption process. We have shown that the relative responses of two polymers can be directly determined from the Gibbs free enthalpy of mixing as determined from NMR measurements performed on neat liquid mixtures. An equivalence of this term-including both enthalpy and entropy contributions-to the energy interaction term calculated using Hansen solubility coefficients, has been demonstrated previously. These results constitute a basis for the development of a numerical program for calculating equilibrium sensor responses. For small molecules, the adsorption kinetics can be easily accounted for by a Fick diffusion coefficient estimated from the Van der Waals volume., (Copyright © 2013 Elsevier B.V. All rights reserved.)

In this work, the influence of surface charge and layer rigidity on Bovin Serum Albumin (BSA) adsorption has been investigated. To this aim, Self Assembled Monolayers (SAMs) bearing terminal COOH or COO(-) groups were built on gold surfaces. The rigidity of the acid terminated SAMs was modified using either an aliphatic, mercaptoundecanoic acid (MUA), or an aromatic, mercaptobenzoic acid (MBA) thiol. X-Ray Photoelectron Spectroscopy (XPS), Polarization Modulation Reflection Absorption Infrared Spectroscopy (PM-RAIRS) and contact angle measurements, were used to deeply characterize the so-built layers. The surface charge was successfully modified by varying the pH of the rinsing solution. Indeed, COOH were the dominating species upon rinsing at pH 2 and COO(-) species dominated upon rinsing at pH 11. Rinsing at an intermediate pH, 5.5, led to the coexistence of both carboxylic and carboxylate moieties. The hydrophilic character of the surface was also found to depend on the rinsing pH, with a minimum after rinsing at intermediate pH. Using aromatic or aliphatic thiols did not affect the speciation but led to considerable differences in the hydrophilic character of these surfaces. Eventually, the adsorption of BSA on the acidic layers was investigated using PM-RAIRS. The results showed interesting differences between the charged layers. Thus, for both MUA and MBA -based SAMs, the amount of adsorbed proteins decreased when the amount of COO(-) on the surface increased. Interestingly, these effects were totally annihilated when the adsorption was carried out in PBS buffer. Moreover, for similar surface charges, the aromatic layers were able to bind higher amounts of proteins than the aliphatic ones. This work points out the key role of both surface charge and rigidity on protein adsorption. The influence of additional parameters, such as hydrophilicity and SAMs' rigidity is also established., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Functionalized silica-based thin films, modified with hydrophobic groups, were synthesized and used as sensors for nitroaromatic compound (NAC) specific detection. Their performance and behavior, in terms of stability, ageing and regeneration, have been fully characterized by combining chemical characterization techniques and electron microscopy. NAC was efficiently and specifically detected using these silica-based sensors, but showed a great degradation in the presence of humidity. Moreover, the sensor sensitivity seriously decreases with storage time. Methyl- and phenyl-functionalization helped to overcome this humidity sensitivity. Surface characterization enabled us to establish a direct correlation between the appearance, and increasing amount, of adsorbed carbonyl-containing species, and sensor efficiency. This contamination, appearing after only one month, was particularly important when sensors were stored in plastic containers. Rinsing with cyclohexane enables us to recover part of the sensor performance but does not yield a complete regeneration of the sensors. This work led us to the definition of optimized elaboration and storage conditions for nitroaromatic sensors.

The mechanism of interaction of Zn porphyrin (ZnPP) with TiO2 surfaces is investigated with a view to optimizing the synthesis of hybrid nanomaterials. The strategy consists of studying the adsorption of ZnPP on TiO2 flat surfaces by taking advantage of complementary surface characterization techniques. Combining a detailed X-ray photoelectron spectroscopic analysis with AFM imaging allows ZnPP-surface and ZnPP intermolecular interactions to be discriminated. Probing the adsorption of ZnPP on TiO2 nanoparticles (NPs) reveals the dominant role of ZnPP-mediated interactions, which are associated with the formation of ZnPP multilayers and/or with the state of aggregation of NPs. These preliminary investigations provide a guideline to synthesizing a novel ZnPP-TiO2 hybrid nanomaterial in a one-step protocol. In this material, ZnPP molecules are presumably involved in the TiO2 lattice rather than on the NP surface. Furthermore, ZnPP molecules preserve their electronic properties within the TiO2 NPs, and this makes the ZnPP-TiO2 hybrid nanomaterial an excellent candidate for nanomedicine and related applications, such as localization of nanoparticles in cells and tissues or in photodynamic therapy., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A chiral pentadecapeptide, l-gramicidine, has been shown to undergo specific adsorption onto gold surfaces modified by chiral amino acids, d- and l-methionine, upon adsorption in the liquid phase. There is a chiral recognition only between the slightly anionic l-peptide and the l-modified surface exhibiting cationic molecules. However, whatever the probe and target molecule charges, very weak recognition was observed between molecules of opposite chirality.

Low-energy electron induced degradation of a model self-assembled monolayer (SAM) of acid terminated alkanethiol was studied under ultra-high vacuum (UHV) conditions at room and low (~40 K) temperatures. Low-energy electron induced chemical modifications of 11-mercaptoundecanoic acid (MUA, HS-(CH2)10-COOH) SAMs deposited on gold were probed in situ as a function of the irradiation energy (<11 eV) by combining two complementary techniques: High Resolution Electron Energy Loss Spectroscopy (HREELS), a surface sensitive vibrational spectroscopy technique, and Electron Stimulated Desorption (ESD) analysis of neutral fragments. The SAM's terminal functions were observed to be selectively damaged at around 1 eV by a resonant electron attachment mechanism, observed to decay by CO, CO2 and H2O formation and desorption. CO2 and H2O were also directly identified at low temperature by vibrational analysis of the irradiated SAMs. At higher irradiation energy, both terminal functions and spacer alkyl chains are damaged upon electron irradiation, by resonant and non-resonant processes.

Matrix isolation is a powerful tool for studying photochemical processes occurring in isolated molecules. In this way, we characterized the chemical modifications occurring within a tri peptide molecule, IGF, when exposed to the influence of Ultraviolet (UV) irradiation. This paper first describes the successful formation of the tripeptide (IGF) argon matrix under vacuum conditions, followed by the in situ UV irradiation and characterization of the molecular matrix reactivity after UV-irradiation. These studies have been performed by combining two complementary spectroscopic techniques, Fourier-Transform Reflexion Absorption Spectroscopy (FT-IRRAS) and X-ray Photoelectron Spectroscopy (XPS). The IR spectra of the isolated peptide-matrix, before and after UV irradiation, revealed significant differences that could be associated either to a partial deprotonation of the molecule or to a tautomeric conversion of some amide bonds to imide ones on some peptide molecules. XPS analyses undoubtedly confirmed the second hypothesis; the combination of IRRAS and XPS results provide evidence that UV irradiation of peptides induces a chemical reaction, namely a shift of the double bond, meaning partial conversion from amide tautomer into an imidic acid tautomer., (Copyright © 2013 Elsevier B.V. All rights reserved.)

In this article, the detection of DNA hybridization taking advantage of the plasmonic properties of gold nanostructures is described. The approach is based on the amplification of the wavelength shift of a multilayered localized surface plasmon resonance (LSPR) sensor interface upon hybridization with gold nanorods and nanostars-labeled DNA. The amplification results in a significant decrease of the limit of detection from ≈40 nM as observed for unlabeled DNA to 0.2 nM for labeled DNA molecules. Furthermore, the plasmonic band, characteristic of the labeled DNA, is different from that of the LSPR interface. Indeed, next to the plasmon band at around 550 nm, being in resonance with the plasmon band of the LSPR interface, additional plasmonic peaks at 439 nm for gold nanostar-labeled DNA and 797 nm for gold nanorod-labeled DNA are observed, which were used as plasmonic signatures for successful hybridization.

In this paper, we report a feasible solvent-free approach for the synthesis and self-assembling of gold nanorods after bioconjugation to antibodies; scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed a remarkable shape and size narrow distribution, as well as a tendency to form linear assemblies on a clean gold surface, upon interaction with antibodies. These bioconjugated gold nanorods were in turns tested in a model Fourier Transform Surface Plasmon Resonance (FT-SPR)-based immunosensor, leading to an improvement of the detection sensitivity by a factor of 8. The results highlight the simplicity of the synthesis protocol of gold nanorods and the interest of using them as labels to enhance the sensitivity of SPR-based sensors., (Copyright © 2012 Elsevier B.V. All rights reserved.)

An antimicrobial peptide, Magainin I (Mag), was grafted to a titanium oxide surface, via an antiadhesive poly(ethylene glycol) (PEG) cross-linker. The latter plays a 2-fold part, being antiadhesive, and enabling the covalent immobilization of the peptide. The functionalization was characterized at each step by reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). The antiadhesive properties of PEG, and antibacterial activity of the anchored Magainin I, were individually tested toward adsorption of bovin serum albumin (BSA) proteins, and against Gram positive bacteria, Listeria ivanovii , respectively. The results reveal that adhesion of both proteins and bacteria have been considerably reduced, accompanied by an inhibition of the growth of remaining adhered bacteria. This work thus offers a novel approach to functionalize oxide surfaces against biofilms and to measure the so-obtained properties in each of the successive steps of a biofilm formation.

To tackle the loss of activity of surfaces functionalized by coating and covalently bound molecules to materials, an intermediate system implying the noncovalent immobilization of active molecules in the inner cavity of grafted cyclodextrins (CDs) was investigated. The antifungal and antibiofilm activities of the most stable complexes of Anidulafungin (ANF; echinocandin) and thymol (THY; terpen) in various CDs were demonstrated to be almost the same as the free molecules. The selected CD was covalently bond to self-assembled monolayers on gold surfaces. The immobilized antifungal agents reduced the number of culturable Candida albicans ATCC 3153 attached to the surface by 64 ± 8% for ANF and 75 ± 15% for THY. The inhibitory activity was persistent for THY-loaded samples, whereas it was completely lost for ANF-loaded surfaces after one use. However, reloading of the echinocandin restored the activity. Using fluorescent dying and confocal microscopy, it was proposed that the ANF-loaded surfaces inhibited the adherence of the yeasts, whereas the activity of immobilized THY was found fungicidal. This kind of tailored approach for functionalizing surfaces that could allow a progressive release of ANF or THY gave promising results but still needs to be improved to display a full activity., (© 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.)

SPR biosensing is increasingly popular for the detection of a multitude of biomolecules. It offers label-free detection and study of proteins, nucleic acids, and other biomolecules in real time. A recent trend involves incorporation of AuNPs, either within the sensing surface itself or as signal enhancing tagging molecules. The importance of AuNP and detecting agent spacing is described and techniques using macromolecular spacing aids are highlighted. Recent methods to enhance SPR detection capabilities using gold nanoparticles are reviewed, as well as device fabrication and the results of incorporation. SPR detection is a highly versatile method for the detection of biomolecules and, with the incorporation of AuNPs, shows promise in extending it to a number of new applications., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Prevention of bacterial adhesion and biofilm formation on the surfaces of materials is a topic of major medical and societal importance. Various synthetic approaches based on immobilization or release of bactericidal substances such as metal derivatives, polyammonium salts and antibiotics were extensively explored to produce antibacterial coatings. Although providing encouraging results, these approaches suffer from the use of active agents which may be associated with side-effects such as cytotoxicity, hypersensibility, inflammatory responses or the progressive alarming phenomenon of antibiotic resistance. In addition to these synthetic approaches, living organisms, e.g. animals and plants, have developed fascinating strategies over millions of years to prevent efficiently the colonization of their surfaces by pathogens. These strategies have been recently mimicked to create a new generation of bio-inspired biofilm-resistant surfaces. In this review, we discuss some of these bio-inspired methods devoted to the development of antibiofilm surfaces. We describe the elaboration of antibacterial coatings based on natural bactericidal substances produced by living organisms such as antimicrobial peptides, bacteriolytic enzymes and essential oils. We discuss also the development of layers mimicking algae surfaces and based on anti-quorum-sensing molecules which affect cell-to-cell communication. Finally, we report on very recent strategies directly inspired from marine animal life and based on surface microstructuring., (Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Adsorption of biomolecules at metal surfaces often creates two-dimensional ordering of the adlayers. However, metal substrate reconstruction is less commonly observed, unless upon annealing of the molecule-surface system. Here, we report on the drastic room-temperature reconstruction of the Au(111) surface, driven by the adsorption of insulin growth factor tripeptide molecules. Scanning tunneling microscopy images show that the surface reconstruction, which takes place without annealing the system, is dynamic and evolves over time. It is initiated at kinks and steps edges, but the reconstruction also takes place within defect-free terraces. Theoretical calculations are performed to explain the reconstruction at the molecular level., (© 2012 American Chemical Society)

Molecular interaction with metal surfaces raises fundamental questions regarding their binding tendency, their dispersion on the surface, as well as their conformation which may change their biological properties; addressing these questions, and being able to tune protein interactions, is of primary importance for the control of biointerfaces. In this study, one tripeptide, GSH (glu-cys-gly), was used to condition gold surfaces and thus influence the adsorption of bovine serum albumin (BSA). Depending on the pH value of the GSH solution, cationic, zwitterionic or anionic forms of the tripeptide could be stabilised on the surface, before interacting with BSA solutions. The amount of proteins was observed to depend both on the chemical state of the adsorbed underlying peptide and on the solvent of the protein solution, indicating an important role of electrostatic interactions upon protein adsorption. Moreover, atomic force microscopy (AFM), and synchrotron IR microscopy revealed a heterogeneous distribution of proteins on the GSH layer.

A direct, label-free immunosensor was designed for the rapid detection and quantification of staphylococcal enterotoxin A (SEA) in buffered solutions using quartz crystal microbalance with dissipation (QCM-D) as transduction method. The sensing layer including the anti-SEA antibody was constructed by chemisorption of a self-assembled monolayer of cysteamine on the gold electrodes placed over the quartz crystal sensor followed by activation of the surface amino groups with the rigid homobifunctional cross-linker 1,4-phenylene diisothiocyanate (PDITC) and covalent linking of binding protein (protein A or protein G). Four anti-SEA antibodies (two of which from commercial source) have been selected to set up the most sensitive detection device. With the optimized sensing layer, a standard curve for the direct assay of SEA was established from QCM-D responses within a working range of 50-1000 or 2000 ngml(-1) with a detection limit of 20 ngml(-1). The total time for analysis was 15 min. Using a sandwich type assay, the response was ca. twice higher and consequently the lowest measurable concentration dropped down to 7 ngml(-1) for a total assay time of 25 min., (Copyright © 2011 Elsevier B.V. All rights reserved.)

This work is focused on studying the grafting of gold nanoparticles (Np) on a cystamine self-assembled monolayer on gold, in order to build sensitive immunosensors. The synthesis and deposition of gold nanoparticles, 13 and 55 nm sizes, were characterised by combining Polarisation Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS), X-ray Photoelectron Spectroscopy (XPS) Surface Enhanced Raman Scattering (SERS), and Atomic Force Microscopy (AFM) which all indicated the formation of a dispersed layer of nanoparticles. This observation is explained by the compromise between the high reactivity of amine-terminated layers towards gold, and interparticle repulsions. Nps were then functionalised with antibody probes, and the recognition by an anti-rIgG was assayed both on planar and Np gold surfaces. The important result is that nanoparticles of 55 nm are preferable for the following reasons: they enable to build a denser and well dispersed layer and they increase both the number of receptors (IgGs) and their accessibility. Beside these geometric improvements, a net enhancement of the Raman signal was observed on the 55 nm nanoparticle layer, making this new platform promising for optical detection based biosensors., (Copyright © 2011 Elsevier B.V. All rights reserved.)

We report the synthesis of diacid-terminated PEG-functionalized cubic TiO(2) nanocrystals by a simple one-step solvothermal method, and their further use to form nanostructured surfaces for protein immobilization. The relevance and major interest of the so-obtained nanocrystals are the presence of terminal carboxylic acid groups at their surface, as confirmed by infrared analyses, in addition to the surrounding PEG chains, essential to avoid non specific interactions. These functional chemical groups were used to (i) immobilize the synthesized nanocubes on a cysteamine-modified Au surface, and to (ii) attach proteins via a presumable covalent link. AFM images show that the shapes and the narrow size distribution of the nanocubes, observed by TEM, were preserved after their immobilization on the modified Au surface. Moreover, the efficiency and specificity of antigen recognition were demonstrated using spectroscopic analyses. Our successful approach provides a versatile and facile way to elaborate specific and sensitive nanostructured surfaces for biosensors.

Antibacterial peptides, magainin I and nisin were covalently bound to stainless steel surfaces. Several procedures of surface functionalisation processes have been investigated and optimized, each step being characterized by polarization modulation reflection absorption infrared spectroscopy (PM-RAIRS) and X-ray photoemission spectroscopy (XPS). Grafting of antibacterial peptides was successfully achieved by a 3 steps functionalisation process on a chitosan polymeric layer. The antibacterial activity of the anchored magainin and nisin was tested against a gram-positive bacteria, Listeria ivanovii, i.e., the possible survival and attachment of this bacteria, was characterized on modified stainless steel surfaces. The results revealed that the adsorbed peptides reduced the adhesion of bacteria on the functionalised stainless steel surface., (Copyright © 2011 Elsevier B.V. All rights reserved.)

A peptide antibiotic, gramicidin A, was covalently bound to cystamine self-assembled monolayers on gold surfaces. Each step of the surface functionalization was characterized by polarization modulation infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy. The antimicrobial activity of the anchored gramicidin was tested against three Gram-positive bacteria (Listeria ivanovii, Enterococcus faecalis, and Staphylococcus aureus), the Gram-negative bacterium Escherichia coli and the yeast Candida albicans. The results revealed that the adsorbed gramicidin reduced, from 60% for E. coli to 90% for C. albicans, the number of culturable microorganisms attached to the surface. The activity was proven to be persistent overtime, up to 6 months after the first use. The bacteria attached to the functionalized surfaces were permeabilized as shown by confocal microscopy. Taken together, these results indicate a bacteriostatic mode of action of the immobilized peptide. Finally, using green fluorescent protein-expressing bacteria, it was shown that the development of a bacterial biofilm was delayed on peptide-grafted surfaces for at least 24 h.

The aim of this work was to create patterned surfaces for localized and specific biochemical recognition. For this purpose, we have developed a protocol for orthogonal and material-selective surface modifications of microfabricated patterned surfaces composed of SiO(2) areas (100 μm diameter) surrounded by Au. The SiO(2) spots were chemically modified by a sequence of reactions (silanization using an amine-terminated silane (APTES), followed by amine coupling of a biotin analogue and biospecific recognition) to achieve efficient immobilization of streptavidin in a functional form. The surrounding Au was rendered inert to protein adsorption by modification by HS(CH(2))(10)CONH(CH(2))(2)(OCH(2)CH(2))(7)OH (thiol-OEG). The surface modification protocol was developed by testing separately homogeneous SiO(2) and Au surfaces, to obtain the two following results: (i) SiO(2) surfaces which allowed the grafting of streptavidin, and subsequent immobilization of biotinylated antibodies, and (ii) Au surfaces showing almost no affinity for the same streptavidin and antibody solutions. The surface interactions were monitored by quartz crystal microbalance with dissipation monitoring (QCM-D), and chemical analyses were performed by polarization modulation-reflexion absorption infrared spectroscopy (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS) to assess the validity of the initial orthogonal assembly of APTES and thiol-OEG. Eventually, microscopy imaging of the modified Au/SiO(2) patterned substrates validated the specific binding of streptavidin on the SiO(2)/APTES areas, as well as the subsequent binding of biotinylated anti-rIgG and further detection of fluorescent rIgG on the functionalized SiO(2) areas. These results demonstrate a successful protocol for the preparation of patterned biofunctional surfaces, based on microfabricated Au/SiO(2) templates and supported by careful surface analysis. The strong immobilization of the biomolecules resulting from the described protocol is advantageous in particular for micropatterned substrates for cell-surface interactions.

Polycyclic aromatic hydrocarbons (PAHs) are a family of contaminants originating from the incomplete combustion of organic compounds, present in the urban air, water, soil and also foodstuff. Due to their recognised carcinogenicity, their concentration in urban air is routinely monitored and governmental instances have set rules as regards their maximum allowable concentration. Benzo[a]pyrene (BaP) is one of the PAHs, highly toxic, whose concentration correlates well with the total PAHs contents in environmental samples; its detection by immunosensors has been rarely described because of its low molecular weight and poor solubility in water. In this paper, we report the design and testing of optical and piezoelectric immunosensors for the determination of BaP by using Polarisation-Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) or Quartz Crystal Microbalance with dissipation measurements (QCM-D) as transduction techniques, and a comparison of their analytical performances. We found relevant to set up immunosensors based on a direct or indirect competitive format. BaP was detected by PM-IRRAS with both immunosensor formats with similar sensitivity, ca. 5 μM. Flow-injection piezoelectric transduction in the indirect competitive format set up led to a slightly better sensitivity than that reached by PM-IRRAS. No general conclusion about the most efficient set up could be drawn from comparing the sensitivities, but the reported data illustrate the potential of PM-IRRAS as well as flow-injection QCM-D as efficient label-free transduction techniques., (Copyright © 2010 Elsevier B.V. All rights reserved.)

This paper describes a controlled way to immobilize gold nanoparticles on planar gold surfaces and the use of the resulting 3D platform to build up a 3D biosensor. The surface was first functionalized by grafting hexanedithiol, this molecule has 2 thiol end groups, which enables its chemical grafting to planar gold while retaining a free thiol group to attach nanoparticles. This step was optimized by varying experimental parameters such as solvent, temperature and immersion time. The grafting was monitored by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). The high resolution XPS sulfur peak made clear the existence of two contributions, S bound to gold and free S, thus led us to determine the optimal conditions to graft hexanedithiol in an extended conformation. 15 nm spherical gold nanoparticles were then immobilized on the resulting surface and their presence was evidenced by surface enhanced Raman spectroscopy (SERS) and atomic force microscopy (AFM). The resulting gold layer was used to build up a 3D biosensor by grafting protein A (PrA), rabbit immunoglobulin (rIgG), and bovine serum albumin (BSA), respectively. Each step was characterized by PM-IRRAS then compared to the results on planar gold surface. Despite the small size of particles and their rather low density on the planar surface, the amount of immobilized proteins, starting from PrA, was almost doubled. The amount of rIgG fixed on the 3D layer was also significantly increased ( approximately 4 times higher than on planar surfaces), however accompanied by a slight decrease of their accessibility, checked by assaying the recognition of a secondary IgG. This work demonstrates the feasibility and interest of building arrays of nanoparticles to immobilize molecular receptors; it also shows that controlling the conditions of elaboration of the biosensor at each step is determining for optimizing the number of molecular receptors., (Copyright (c) 2010 Elsevier B.V. All rights reserved.)