Search

Recent advances in technology are expected to increase our current understanding of neuroscience. Nanotechnology and nanomaterials can alter and control neural functionality in both

Molybdenum dioxide (MoO2), considering its near-metallic conductivity and surface plasmonic properties, is a great material for electronics, energy storage devices and biosensing. Yet to this day, room-temperature synthesis of large area MoO2, which allows deposition on arbitrary substrates, has remained a challenge. Due to their reactive interfaces and specific solubility conditions, gallium-based liquid metal alloys offer unique opportunities for synthesizing materials that can meet these challenges. Herein, a substrate-independent liquid metal-based method for the room temperature deposition and patterning of MoO2 is presented. By introducing a molybdate precursor to the surrounding of a eutectic gallium-indium alloy droplet, a uniform layer of hydrated molybdenum oxide (H2MoO3) is formed at the interface. This layer is then exfoliated and transferred onto a desired substrate. Utilizing the transferred H2MoO3 layer, a laser-writing technique is developed which selectively transforms this H2MoO3 into crystalline MoO2 and produces electrically conductive MoO2 patterns at room temperature. The electrical conductivity and plasmonic properties of the MoO2 are analyzed and demonstrated. The presented metal oxide room-temperature deposition and patterning method can find many applications in optoelectronics, sensing, and energy industries.

This paper describes the synthesis of a new type of nanowires, potassium tetracyanoplatinate sesquihydrate Krogmann salt or K(def)TCP. Seed-mediated electrocrystallization nucleates and confines the K(def)TCP crystals into nanowires. Our data show that the width of K(def)TCP scales proportionally with the diameter of the seed, which is consistent with the nanoconfinement effect of the seed. K(def)TCP nanowires are also electrodeposited on lithographic Au patterns as interconnects and tested for impedance-based gas sensing. The results demonstrate the use of electrocrystallization to construct nanowire sensing units directly on patterned substrates to enable scaling up of nanowire sensor technology. IMPACT STATEMENT We show for the first time nanowires directly formed as interconnects on electronic substrates by electrocrystallization are used as sensor materials to detect gases.

Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken into account in colloidal dispersion formulations.

Langmuir–Blodgett films of metallosurfactants were used in Au|molecule|Au devices to investigate the mechanisms of current rectification.

Nanopatterns have applications in many areas including sensors, optoelectronics, and crystallization screening. Particle lithography is a convenient method to manufacture nanoring nanopatterns based on organosilane surface chemistry. The pattern thickness is generally limited to the monolayer thickness. This work is focused on the chemical vapor deposition conditions that yield nanopatterns with multilayer thickness. The supra-monolayer n-octadecyltrichlorosilane (OTS) nanoring patterns are made using polystyrene particle lithography. The supra-monolayer nanopatterns are used as "nano-flasks" to deposit and nucleate nanoparticles of small organic molecules including n-docosane, aspirin, and clarithromycin. The supra-monolayer OTS nanopattern is an effective template for nanoparticle array deposition of all three chemicals with high degree of fidelity to the substrate pattern. The nanoparticle size is varied by solution concentration. The preferential deposition of the organic molecules inside the nanoring is attributed to the dewetting of the liquid film on the nanopattern. The dewetting process effectively distributes the liquid film among the "nano-flasks" so that millions of solution experiments can be carried out in isolated droplets with droplet volume as small as 1×10(-10) nL. The research demonstrates a method to manufacture "nano-flask" arrays for high-throughput nanoparticle deposition trials and manufacture of monodisperse organic/drug nanoparticles through self-assembly.

This paper describes nanorod formation induced by nanoparticle seeds. Carboxylic acids self-assemble on graphite into an epitaxial pattern. However, this persistent pattern is changed into nanorods by nanoparticles. Two control parameters have been identified, including nucleus/substrate contact angle and seed-to-critical nucleus size ratio. Effective carboxylic chain length and nanoparticle size range are identified, which can be related to the seed size effect. Some nanorods are detached when methyl-terminated nanoparticles are used, and the percentage of detached nanorods increases with increasing carbon chain length. In contrast, the nanorods do not detach from carboxyl-terminated nanoparticles. This study offers direct experimental evidence to molecular simulation prediction that nuclei display a confined morphology on a highly curved seed surface due to the difficulty of maintaining an unstrained structure and they readily detach from the surface during heterogeneous crystal nucleation. This study c...

The effect of cross-linking layer-by-layer (LbL) films consisting of bioreducible poly(2-dimethylaminoethyl methacrylate) (rPDMAEMA) and DNA is examined with regard to rigidity, biodegradability, cell adhesion, and transfection activity using 1,5-diiodopentane (DIP) cross-linker. DIP chemically reacts with the tertiary amines of rPDMAEMA, altering the chemical composition of these LbL films. The result is a change in surface morphology, film swelling behavior, and film rigidity, measured with AFM and ellipsometry. It is found that the apparent Young's modulus is increased more than 4 times its original value upon cross-linking. Cross-linking mass is additionally confirmed with a quartz crystal microbalance with dissipation (QCM-D). Comprehensive analyses of these experimental values were investigated to calculate the degree of cross-linking using the rubber elasticity theory and the Flory-Rehner theory. Additionally, the Flory-Huggins parameter, chi, was calculated. Good agreement in the two methods yields a cross-linking density of approximately 0.82 mmol/cm(3). The Flory-Huggins parameter increased upon cross-linking from 1.07 to 1.2, indicating increased hydrophobicity of the network and formation of bulk water droplets within the films. In addition, the effects of cross-linking on film disassembly by 1,4-dithiothreitol (DTT) are found to be insignificant despite the alteration in film rigidity. Mouse fibroblast cells and smooth muscle cells are used to study the effect of cross-linking on cell adhesion and cell transfection activity. In vitro transfection activity up to seven days is quantified using secreted alkaline phosphatase (SEAP) DNA. Film cross-linking is found to enhance cell adhesion and prolong the duration of cellular transfection. These results contribute to the development of bioreducible polymer coatings for localized gene delivery.

Dendrimers, with their well-defined globular shape and a high density of functional groups, are ideal nanoscale materials for templating sensor surfaces. This work exploits dendrimers as a versatile platform for capturing biomarkers with improved sensitivity and specificity. Synthesis, characterization, fabrication, and functional validation of the dendrimer-based assay platform are described. Bifunctional hydroxyl/thiol functionalized G4-polyamidoamine (PAMAM) dendrimer is synthesized and immobilized on to the polyethylene-glycol (PEG)-functionalized assay plate by coupling PEG-maleimide and dendrimer thiol groups. Simultaneously, part of the dendrimer thiol groups are converted to hydrazide functionalities. The resulting dendrimer-modified surface is coupled to the capture antibody in the Fc region of the oxidized antibody. This preserves the orientation flexibility of the antigen binding region (Fv) of the antibody. To validate the approach, the fabricated plates are further used as a solid phase for developing a sandwich type ELISA to detect IL-6 and IL-1β, important biomarkers for early stages of chorioamnionitis. The dendrimer-modified plate provides assays with significantly enhanced sensitivity, lower nonspecific adsorption, and a detection limit of 0.13 pg ml-1 for IL-6 luminol detection and 1.15 pg ml-1 for IL-1β TMB detection, which are significantly better than those for the traditional ELISA. The assays were validated in human serum samples from normal (non-pregnant) woman and pregnant women with pyelonephritis. The specificity and the improved sensitivity of the dendrimer-based capture strategy could have significant implications for the detection of a wide range of cytokines and biomarkers since the capture strategy could be applied to multiplex microbead assays, conductometric immunosensors and field effect biosensors.

ENATBIO: a National Conference on Emerging Nanoscience in Technology and Biomedicine Guangzhao Mao, PhD, Golam Newaz, Chiming Wei, MD, PhD⁎ Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, Michigan, USA Department of Mechanical Engineering, Wayne State University, Detroit, Michigan, USA Department of Surgery, Johns Hopkins University School of Medicine, Ellicott City, Maryland, USA

The possibility of using surface topography for guidance of different biological molecules and cells is a relevant topic that can be applied to a wide research activity. This study investigated the adsorption of fibronectin to a diffraction grated silicon surface. The rectangular grating profile featured a controlled surface with 350 nm period and a corrugation depth of 90 nm. Results demonstrated that the controlled surface had a significantly positive effect on the fibronectin binding. Thus, nanoscale surface topography can enhance fibronectin binding.

Poor drug encapsulation efficiency and rapid release of the encapsulated drug limit the use of nanoparticles in biomedical applications involving water-soluble drugs. We have developed a novel polymer-surfactant nanoparticle formulation, using the anionic surfactant Aerosol OT (AOT) and polysaccharide polymer alginate, for sustained release of water-soluble drugs. Particle size of nanoparticles, as determined by atomic force microscopy and transmission electron microscopy, was in the range of 40-70 nm. Weakly basic molecules like methylene blue, doxorubicin, rhodamine, verapamil, and clonidine could be encapsulated efficiently in AOT-alginate nanoparticles. In vitro release studies with basic drug molecules indicate that nanoparticles released 60-70% of the encapsulated drug over 4 weeks, with near zero-order release during the first 15 days. Studies with anionic drug molecules demonstrate poorer drug encapsulation efficiency and more rapid drug release than those observed with basic drugs. Further studies investigating the effect of sodium concentration in the release medium and the charge of the drug suggest that calcium-sodium exchange between nanoparticle matrix and release medium and electrostatic interaction between drug and nanoparticle matrix are important determinants of drug release. In conclusion, we have formulated a novel surfactant-polymer drug delivery carrier demonstrating sustained release of water-soluble drugs.

This paper reports the disassembly of layer-by-layer (LbL) films of plasmid DNA and a reducible cationic polypeptide. To utilize a reducing microenvironment of cellular plasma membrane as a potential trigger, LbL films are assembled to contain both DNA and the TAT-based polypeptide (PTAT) with reducible disulfide bonds in the backbone. The assembly and disassembly processes are monitored by goniometry, ellipsometry, and atomic force microscopy (AFM). The structure of the PTAT films is compared with that of non-reducible poly( l -lysine) (PLL) films. Both PTAT and PLL films exhibit exponential growth but with the contact angle alternating between characteristic values. Ellipsometry and AFM show a gradual and complete disassembly of the PTAT but not the PLL films in a 24 h period in the reducing environment in vitro. This study suggests a potential of using reducible LbL films for controlled DNA delivery.

Increasingly, organosilane self-assembled monolayers (SAMs) are used to modify the surfaces of silicon-based sensors and atomic force microscope (AFM) probes. Organosilane SAMs are preferred due to their fast and easy preparation, stability, and applicability to a wide range of substrates. The traditional dip coating method from solution often yields ill-defined particulate aggregates on the two-dimensional SAM. The presence of such three-dimensional aggregates seriously reduces the performance of miniaturized biosensor devices and AFM probes. It is difficult to control the amount of water in solution-based deposition. This paper describes a chemical vapor deposition (CVD) method to deposit octadecyltrichlorosilane (OTS) monolayers on silicon wafers and AFM probes under vacuum condition. OTS coated surfaces with static water contact angle ranging from 20° to 107° can be obtained by controlling the deposition conditions. The silicon substrates and AFM probes after CVD are characterized by AFM, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and contact angle goniometry. The OTS monolayer is in a uniform low-density state below 65%. Above 65%, densely packed crystalline-like domains start to form. It takes 24 h to reach the adsorption saturation. The time span in the CVD deposition is much longer than the solution case and thus allowing precise variation of the substrate hydrophobicity for biosensor applications.

Layer-by-layer (LbL) films containing cationic polyelectrolytes and anionic bioactive molecules such as DNA are promising biomaterials for controlled and localized gene delivery for a number of biomedical applications including cancer DNA vaccine delivery. Bioreducible LbL films made of disulfide-containing poly(amido amine)s (PAAs) and plasmid DNA can be degraded by redox-active membrane proteins through the thiol-disulfide exchange reaction to release DNA exclusively into the extracellular microenvironment adjacent to the film. In order to better understand the film degradation mechanism and nature of the released species, the bioreducible film degradation is studied by atomic force microscopy, fluorescence, and dynamic light scattering in solutions containing a reducing agent. The PAA/DNA LbL film undergoes fast bulk degradation with micrometer-sized pieces breaking off from the substrate. This bulk degradation behavior is arrested by periodic insertions of a nonbioreducible poly(ethylenimine) (PEI) layer. The LbL films containing PAA/DNA and PEI/DNA bilayers display sequential film disassembly and are capable of continuously releasing DNA nanoparticles over a prolonged time. Insertion of the PEI layer enables the bioreducible LbL films to transfect human embryonic kidney 293 cells. The data conclude that the PEI layer is effective as a barrier layer against interlayer diffusion during LbL film assembly and more importantly during film disassembly. Without the barrier layer, the high mobility of cleaved PAA fragments is responsible for bulk degradation of bioreducible LbL films, which may prevent their ultimate gene-delivery applications. This work establishes a direct link among film internal structure, disassembly mechanism, and transfection efficiency. It provides a simple method to design bioreducible LbL films for sequential and long-time DNA release.

This paper reports the synthesis and characterization of polystyrene nanorods in hemicylindrical hemimicelles of a nonionic polyoxyethylene surfactant, C 12 E 5, on graphite. The surface structure is characterized by atomic force microscopy (AFM), Fourier transform infrared spectroscopy, and contact angle goniometry. Uniformly aligned polystyrene nanorods are captured by AFM. The nanorod dimensions are studied as a function of the reaction time and styrene monomer concentration. The template synthesis using self-assembled surfactant surface aggregates promises to create functional and stable nanostructures for optoelectronics and surface engineering.

The self-associating structures at the solid-liquid interface of three nonionic trisiloxane surfactants ((CH3)3SiO)2Si(CH3)(CH2)3(OCH2CH2)n OH (n = 6, 8, and 12), or BEn, are studied as a function of substrate properties by atomic force microscopy (AFM) imaging and force measurement. These trisiloxane surfactants are known as superwetters, which promote rapid spreading of dilute aqueous solutions on low-energy surfaces. This study also attempts to relate the BEn surface aggregate structures at the solid-liquid interface to their superwetting behavior. Four substrates are used in the study: muscovite mica, highly oriented pyrolytic graphite, and oxidized silicon wafer with and without a full monolayer of self-assembled n-octadecyltrichlorosilane (OTS). The concentration of BEn is fixed at 2 times the critical aggregation concentration (CAC). The BEn surfactants are only weakly attracted to hydrophilic surfaces, more on oxidized silicon than on mica. All three form ordinary planar monolayers on HOPG and OTS-covered oxidized silicon. The significance of surfactant adsorption on the AFM tip is investigated by comparing the force curves obtained by tips with and without thiol modification. The surface aggregate structures of the BEn surfactants correlate with their bulk structures and do not exhibit anomalous adsorption behavior. The adsorption behavior of the BEn superwetters is similar to that of the CmEn surfactants. Thus, our results confirm previous work showing that superwetting shares its main features with other classes of surfactants.

We investigate the making of semiconductor nanorods using well-defined molecular templates. The films are characterized by AFM and XPS. The spin-coated monolayer of arachidic acid assembles on graphite as 1D nanostripes with bilayer periodicity. The copper arachidate film shows curved stripes, which become straight after reacting with hydrogen sulfide. The new template scheme may facilitate the fabrication of nanorod arrays of a variety of inorganic and semiconducting materials.

Synthetic vector-based gene delivery continues to gain strength as viable alternatives to viral vectors due to safety and other concerns. DNA release dynamics is key to the understanding and control of gene delivery from nanosystems. Here we describe atomic force microscope (AFM) application to the understanding of DNA release dynamics from bioreducible polycation-based nanosystems. The two nanosystems are polyplex nanoparticles and layer-by-layer (LbL) films.

This paper describes the formation of organic nanorods induced by monolayer-protected inorganic nanoparticles. Alkanes and alkane derivatives, such as n-carboxylic acids, self-assemble on highly oriented pyrolytic graphite (HOPG) into a persistent molecular packing structure that is dictated by the epitaxial interaction between the carbon chain plane and the HOPG basal plane. Carboxylic acids form 2-D crystalline layers consisting of nanostripe domains whose periodicity is one or two times the molecular chain length. However, when the molecular ordering occurs in the vicinity of a nanoparticle, this persistent HOPG-dominated nanostripe pattern is disrupted, and nanorods attached to the nanoparticles become the dominant structure. In order to understand the underlying mechanism of the nanoparticle-mediated nanorod formation, the effects of film-forming conditions, carboxylic acid chain length, nanoparticle size, and chemical composition of the nanoparticle are examined. It is determined that carboxylic acid nanorods can be induced by nanoparticles of different core materials including CdSe, CdS, and Au, as long as the protecting monolayer allows sufficient dispersion and colloidal stability of the nanoparticles in solution. A carboxylic chain length range amenable to the nanorod formation is identified, as is the relationship between the nanoparticle size and the number of nanorods per nanoparticle. This study contributes to the understanding of seed-mediated crystallization and molecular ordering. Moreover, it defines the parameters governing solution-based formation of hybrid nanostructures and nanopatterns incorporating dual functionality as defined by the inorganic nanoparticle and organic nanorod, respectively.

DNA release dynamics from layer-by-layer (LbL) films is an important aspect to consider with regards to localized gene delivery systems. The rate of DNA release and the condensation state of DNA during release are of particular interest in the field of gene delivery. A hyperbranched poly(amido amine) (RHB) containing bioreducible disulfide bonds is used to form interpolyelectrolyte complexes with DNA during LbL film assembly. During film disassembly, DNA is released in physiologic conditions due to the reducing nature of the RHB. Uncondensed DNA deposited on the surface was compared to DNA condensed by RHB in polyplex form by using two types of LbL films, RHB/DNA/RHB and polyplex terminated films, RHB/DNA/polyplex. LbL films with up to three layers are used in order to facilitate high-resolution atomic force microscopy (AFM) imaging. X-ray reflectivity, ellipsometry, and Fourier transform infrared spectroscopy are also used. The film disassembly, rearrangement, and release of molecules from the surface due to thiol-disulfide exchange is conducted in reducing dithiothreitol (DTT) solutions. Salt is found to accelerate the overall rate of film disassembly. Additionally, it was found that the polyplex layer disassembles faster than the DNA layer. The predominant intermediate structure is the toroid structure for the polyplex layer and the fiber bundle structure for the DNA layer during film disassembly. This study offers a simple means to modulate DNA release from LbL films by utilizing both condensed and uncondensed DNA in different layers. The study highlights nanostructures, toroids, and bundles as dominant intermediate DNA structures during DNA release from LbL films.

Two-dimensional periodic structures with nanometer feature sizes have been widely used in many photonic devices. The profile and size of the nanostructure elements can greatly affect optical performances. Various practical subwavelength structures working in the visible and near infrared region have been fabricated using electron-beam writing or laser interference techniques. In this paper, we present a new technique which use nanosphere lithography (NSL) and reactive-ion etching to fabricate two-dimensional nanostructures with tunable nanoelement size and profile.

We use the self-assembled polystyrene nanosphere monolayer pattern to replace photoresist mask for the fabrication of 2D nanostructures on various substrates. The optical properties of these artificial structures are measured and compared with theoretical calculation.

This communication describes a spin-coating method to nucleate organic molecular rods of uniform size from an inorganic nanoparticle at a solid surface. The particle-rod hybrid structure spontaneously forms when a film is spin coated from a mixed 2-propanol solution of arachidic acid (AA) and nanoparticles of cadmium selenide capped by mercaptoundecanoic acid (MUA-CdSe) on graphite. AFM images show that MUA-CdSe nanoparticles nucleate single crystalline rods of AA with a cross section of a single unit cell of the C-form. The solution-based process potentially allows the precise tuning of the wetting profile of the solution on the surface-attached nanoparticle, which provides the reservoir for the growth of the single crystalline rods. The results suggest that nanoparticles can be regarded as nanoseeds for the nucleation of guest crystals. It should be possible to further functionalize the AA rods by electrostatic complexation with metal or organic ions.

We have created nanospirals by self-assembly during droplet evaporation. The nanospirals, 60–70 nm in diameter, formed when solvent mixtures of methanol and m-cresol were used. In contrast, spin coating using only methanol as the solvent produced epitaxial films of stripe nanopatterns and using only m-cresol disordered structure. Due to the disparity in vapor pressure between the two solvents, droplets of m-cresol solution remaining on the substrate serve as templates for the self-assembly of carboxylic acid molecules, which in turn allows the visualization of solution droplet evaporation one molecule at a time.

A new approach to the generation of nanoparticle arrays in periodic as well as non-periodic fashions has been discovered based on reduction of oxidized nanoscroll/nanoribbon precursors in the transmission electron microscope (carbothermal reduction) or by hydrogen annealing. Arrays consisting of nickel arsenide nanoparticles of size 3-4 nm have been generated.