Thickness-dependent humidity sensing by poly(vinyl alcohol) stabilized Au-Ag and Ag-Au core-shell bimetallic nanomorph resistors.

We herein report a simple chemical route to prepare Au-Ag and Ag-Au core-shell bimetallic nanostructures by reduction of two kinds of noble metal ions in the presence of a water-soluble polymer such as poly(vinyl alcohol) (PVA). PVA was intentionally chosen as it can play a dual role of a supporting matrix as well as stabilizer. The simultaneous reduction of metal ions leads to an alloy type of structure. Ag(c)-Au(s) core-shell structures display tendency to form prismatic nanostructures in conjunction with nanocubes while Au(c)-Ag(s) core-shell structures show formation of merely nanocubes. Although UV-visible spectroscopy and X-ray photoelectron spectroscopy analyses of the samples typically suggest the formation of both Ag(c)-Au(s) and Au(c)-Ag(s) bimetallic nanostructures, the definitive evidence comes from high-resolution transmission electron microscopy-high-angle annular dark field elemental mapping in the case of Au(c)-Ag(s) nanomorphs only. The resultant nanocomposite materials are used to fabricate resistors on ceramic rods having two electrodes by drop casting technique. These resistors are examined for their relative humidity (RH) response in the range (2-93% RH) and both the bimetallic nanocomposite materials offer optimized sensitivity of about 20 Kohm/% RH and 300 ohm/% RH at low and higher humidity conditions, respectively, which is better than that of individual nanoparticles.

Fluorescence-based immunosensor using three-dimensional CNT network structure for sensitive and reproducible detection of oral squamous cell carcinoma biomarker.

A hierarchical three-dimensional network of carbon nanotubes on Si pillar substrate (3DN-CNTs) was developed for the accurate detection of oral squamous cell carcinoma (OSCC) in clinical saliva samples. The 3DN-CNTs were uniformly coated with a layer of aluminum oxides to enhance structural stability during biomarker detection. Cytokeratin-19 antigen (Cyfra 21-1) was utilized as a model biomarker of OSCC for fluorescence-based immunosensor using 3DN-CNTs (3DN-CNTs sensor). The 3DN-CNTs sensor enhances the sensitivity of Cyfra 21-1 detection by increasing the density of immobilized antibody through high surface area of 3DN-CNTs and enhancing the accessibility of biomolecules through the ordered pathway of hierarchical structure. The reliable detection limit for sensing of Cyfra 21-1 was estimated as in the level of 0.5 ng/mL and the quantitative estimation of Cyfra 21-1 was analyzed by 4-parameter logistic (4-PL) model for curve-fitting analysis. Clinical applicability of 3DN-CNTs sensor was evaluated through correlation with the commercially available electrochemiluminescence (ECL) detection system in the hospital. The assay results of the two systems for clinical saliva samples showed a good linear correlation. The 3DN-CNTs sensor offers great potential for accurate diagnosis of OSCC using Cyfra 21-1 biomarker in clinical fluids.

Designing Ecofriendly Bionanocomposite Assembly with Improved Antimicrobial and Potent on-site Zika Virus Vector Larvicidal Activities with its Mode of Action.

Dialyzed natural polymer, fibroin, from Bombyx mori was used to synthesize biocompatible silver and gold nanoparticles in-situ in dispersion form. The films of pure fibroin (PF), fibroin-silver nanocomposite (FSNC) and fibroin-gold nanocomposite (FGNC) were fabricated by drop casting method. The characterization of the resultant dispersion and films was performed by visual color change, UV-Vis spectroscopy and atomic force microscopy. The dispersions of PF, FSNC and FGNC were tested for antibacterial activity against E. coli NCIM 2065, S. aureus NCIM 5021, K. pneumoniae NCIM 2957, P. aeruginosa ATCC 9027 and antifungal activity against A. fumigatus NCIM 902. FSNC dispersion exhibited an effective antimicrobial action against all the tested microbes as compared to FGNC dispersion. The mechanism of action for FSNC and FGNC against these microorganisms is proposed. Additionally, the larvicidal activity of the films was investigated against the larvae of Aedes aegypti. The films of FSNC exhibited 100% mortality while the films of FGNC revealed 86-98% mortality against all the larval instars and pupae of A. aegypti. The phytotoxicity study of the nanocomposite films was also carried out to confirm the reusability of water. This is first noble metal nanocomposite based report on larvicidal activity of zika virus vector.

Swift tuning from spherical molybdenum microspheres to hierarchical molybdenum disulfide nanostructures by switching from solvothermal to hydrothermal synthesis route.

Herein, we report the synthesis of metallic molybdenum microspheres and hierarchical MoS2 nanostructures by facile template-free solvothermal and hydrothermal approach, respectively. The morphological transition of the Mo microspheres to hierarchical MoS2 nanoflower architectures is observed to be accomplished with change in solvent from ethylenediamine to water. The resultant marigold flower-like MoS2 nanostructures are few layers thick with poor crystallinity while spherical ball-like molybdenum microspheres exhibit better crystalline nature. This is the first report pertaining to the synthesis of Mo microspheres and MoS2 nanoflowers without using any surfactant, template or substrate in hydro/solvothermal regime. It is opined that such nanoarchitectures of MoS2 are useful candidates for energy related applications such as hydrogen evolution reaction, Li ion battery and pseudocapacitors. Inquisitively, metallic Mo can potentially act as catalyst as well as fairly economical Surface Enhanced Raman Spectroscopy (SERS) substrate in biosensor applications.

A label-free electrochemical immunosensor for the detection of cardiac marker using graphene quantum dots (GQDs).

A label-free immunosensor based on electrochemical impedance spectroscopy has been developed for the sensitive detection of a cardiac biomarker myoglobin (cMyo). Hydrothermally synthesized graphene quantum dots (GQDs) have been used as an immobilized template on screen printed electrodes for the construction of an impedimetric sensor platform. The GQDs-modified electrode was conjugated with highly specific anti-myoglobin antibodies to develop the desired immunosensor. The values of charge transfer resistance (Rct) were monitored as a function of varying antigen concentration. The Rct value of the immunosensor showed a linear increase (from 0.20 to 0.31kΩ) in the range of 0.01-100ng/mL cMyo. The specific detection of cMyo was also made in the presence of other competing proteins. The limit of detection for the proposed immunosensor was estimated as 0.01ng/mL which is comparable to the standard ELISA techniques.

Neuroprotective and antioxidant activities of bamboo salt soy sauce against H2O2-induced oxidative stress in rat cortical neurons.

Bamboo salt (BS) and soy sauce (SS) are traditional foods in Asia, which contain antioxidants that have cytoprotective effects on the body. The majority of SS products contain high levels of common salt, consumption of which has been associated with numerous detrimental effects on the body. However, BS may be considered a healthier substitute to common salt. The present study hypothesized that SS made from BS, known as bamboo salt soy sauce (BSSS), may possess enhanced cytoprotective properties; this was evaluated using a hydrogen peroxide (H2O2)-induced neuronal cell death rat model. Rat neuronal cells were pretreated with various concentrations (0.001, 0.01, 0.1, 1 and 10%) of BSSS, traditional soy sauce (TRSS) and brewed soy sauce (BRSS), and were subsequently exposed to H2O2 (100 µM). The viability of neuronal cells, and the occurrence of DNA fragmentation, was subsequently examined. Pretreatment of neuronal cells with TRSS and BRSS reduced cell viability in a concentration-dependent manner, whereas neuronal cells pretreated with BSSS exhibited increased cell viability, as compared with non-treated neuronal cells. Furthermore, neuronal cells pretreated with 0.01% BSSS exhibited the greatest increase in viability. Exposure of neuronal cells to H2O2 significantly increased the levels of reactive oxygen species (ROS), B-cell lymphoma 2-associated X protein, poly (ADP-ribose), cleaved poly (ADP-ribose) polymerase, cytochrome c, apoptosis-inducing factor, cleaved caspase-9 and cleaved caspase-3, in all cases. Pretreatment of neuronal cells with BSSS significantly reduced the levels of ROS generated by H2O2, and increased the levels of phosphorylated AKT and phosphorylated glycogen synthase kinase-3ß. Furthermore, the observed effects of BSSS could be blocked by administration of 10 µM LY294002, a phosphatidylinositol 3-kinase inhibitor. The results of the present study suggested that BSSS may exert positive neuroprotective effects against H2O2-induced cell death by reducing oxidative stress, enhancing survival signaling, and inhibiting death signals.

A 3D networked polydiacetylene sensor for enhanced sensitivity.

A three order sensitivity enhancement over a 2D system was achieved with a polydiacetylene-immobilized 3D networked sensor matrix.

Control over Neurite Directionality and Neurite Elongation on Anisotropic Micropillar Arrays.

Control over neurite orientation in primary hippocampal neurons is achieved by using interrupted, anisotropic micropillar arrays as a cell culture platform. Both neurite orientation and neurite length are controlled by a function of interpillar distance.

Enhanced Acid Diffusion Control by Using Photoacid Generator Bound Polymer Resist.

Photoacid generators (PAGs) have been widely used as a key component for improving photoresist performance. The acid diffusion influences on the photoresist characteristics of resolution and line edge roughness (LER). The PAG bound polymer resist has been a key component for solving the problems of PAG aggregation and acid diffusion control. A triphenyl sulfonium salt methacrylate as PAG was synthesized and copolymerized with crosslinkable glycidyl methacrylate and methyl methacrylate by radical reaction for a new PAG bound polymer resist. The characterization of resist polymers was carried out by 1H NMR. The lithographic performance of photoresists was investigated by ArF lithography. Both PAG bound resist and the PAG blended resist were employed to demonstrate the effect of PAG unit in a resist system. The polymer bound PAG resist improved the LER and showed a higher resolution than the PAG blend resist.

Gold Nanowire Bundles Grown Radially Outward from Silicon Micropillars.

One-dimensional (1D) micro- and nanostructures have become increasingly popular because of their tremendous prospect in various applications. While the design and fabrication of these structures from a single component in two-dimensional (2D) arrays is common, the attainment of hierarchical three-dimensional (3D) architectures made up of multicomponent one-dimensional structures is rare. Herein we report, for the first time, the lateral growth of gold nanowires from the sidewalls of substrate grown silicon micropillars to form a unique "wire-on-pillar" architecture. Unlike zero-dimensional (0D) point-like, 1D linear, and 2D planar Au structures, the obtained 3D "wire-on-pillar" Au architecture provides abundant hotspots between adjacent Au wires, which led to remarkably high surface-enhanced Raman scattering (SERS) signals.

Bio-inspired Hierarchical Nanowebs for Green Catalysis.

Bio-inspired 3D hierarchical nanowebs are fabricated using silicon micropillars, carbon nanotubes (CNT), and manganese oxide. The Si pillars act as artificial branches for growing CNTs and the secondary metal coating strengthens the structures. The simple but effective structure provides both chemical and mechanical stability to be used as a green catalyst for recycling waste polymers into raw materials.

Elucidating how bamboo salt interacts with supported lipid membranes: influence of alkalinity on membrane fluidity.

Bamboo salt is a traditional medicine produced from sea salt. It is widely used in Oriental medicine and is an alkalizing agent with reported antiinflammatory, antimicrobial and chemotherapeutic properties. Notwithstanding, linking specific molecular mechanisms with these properties has been challenging to establish in biological systems. In part, this issue may be related to bamboo salt eliciting nonspecific effects on components found within these systems. Herein, we investigated the effects of bamboo salt solution on supported lipid bilayers as a model system to characterize the interaction between lipid membranes and bamboo salt. The atomic composition of unprocessed and processed bamboo salts was first analyzed by mass spectrometry, and we identified several elements that have not been previously reported in other bamboo salt preparations. The alkalinity of hydrated samples was also measured and determined to be between pH 10 and 11 for bamboo salts. The effect of processed bamboo salt solutions on the fluidic properties of a supported lipid bilayer on glass was next investigated by fluorescence recovery after photobleaching (FRAP) analysis. It was demonstrated that, with increasing ionic strength of the bamboo salt solution, the fluidity of a lipid bilayer increased. On the contrary, increasing the ionic strength of near-neutral buffer solutions with sodium chloride salt diminished fluidity. To reconcile these two observations, we identified that solution alkalinity is critical for the effects of bamboo salt on membrane fluidity, as confirmed using three additional commercial bamboo salt preparations. Extended-DLVO model calculations support that the effects of bamboo salt on lipid membranes are due to the alkalinity imparting a stronger hydration force. Collectively, the results of this work demonstrate that processing of bamboo salt strongly affects its atomic composition and that the alkalinity of bamboo salt solutions contributes to its effect on membrane fluidity.

A Highly Sensitive and Reliable Strain Sensor Using a Hierarchical 3D and Ordered Network of Carbon Nanotubes.

A 3D network of single-walled carbon nanotubes embedded in poly-(dimethylsiloxane) is presented as a promising route to the fabrication of a flexible film with ordered and interconnected single-walled carbon nanotubes. This is possible using a simple transfer method of as-grown hierarchical single-walled carbon nanotubes on a Si pillar substrate. This film is used as a highly sensitive strain gauge sensor. This type of network embedded in a polymer film should be applicable to many fields involving mechanically stable and reliable strain sensors.

Contribution of temperature to deformation of adsorbed vesicles studied by nanoplasmonic biosensing.

With increasing temperature, biological macromolecules and nanometer-sized aggregates typically undergo complex and poorly understood reconfigurations, especially in the adsorbed state. Herein, we demonstrate the strong potential of using localized surface plasmon resonance (LSPR) sensors to address challenging questions related to this topic. By employing an LSPR-based gold nanodisk array platform, we have studied the adsorption of sub-100-nm diameter 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid vesicles on titanium oxide at two temperatures, 23 and 50 °C. Inside this temperature range, DPPC lipid vesicles undergo the gel-to-fluid phase transition accompanied by membrane area expansion, while DOPC lipid vesicles remain in the fluid-phase state. To interpret the corresponding measurement results, we have derived general equations describing the effect of deformation of adsorbed vesicles on the LSPR signal. At the two temperatures, the shape of adsorbed DPPC lipid vesicles on titanium oxide remains nearly equivalent, while DOPC lipid vesicles become less deformed at higher temperature. Adsorption and rupture of DPPC lipid vesicles on silicon oxide were also studied for comparison. In contrast to the results obtained on titanium oxide, adsorbed vesicles on silicon oxide become more deformed at higher temperature. Collectively, the findings demonstrate that increasing temperature may ultimately promote, hinder, or have negligible effect on the deformation of adsorbed vesicles. The physics behind these observations is discussed, and helps to clarify the interplay of various, often hidden, factors involved in adsorption of biological macromolecules at interfaces.

TiO2 particles on a 3D network of single-walled nanotubes for NH3 gas sensors.

Ammonia (NH3) gas is one of the gases which causes damage to environment such as acidification and climate change. In this study, a gas sensor based on the three-dimensional (3D) network of single-walled nanotubes (SWNTs) was fabricated for the detection of NH3 gas in dry air. The sensor showed enhanced performance due to the fast gas diffusion rate and weak interactions between the carbon nanotubes and the substrate. Metal oxide particles were introduced to enhance the performance of the gas sensor. Atomic layer deposition (ALD) was employed to deposit the metal oxide in the complex structure, and good control over thickness was achieved. The hybrid gas sensor consisting of the 3D network of SWNTs with anatase TiO2 particles showed stable, repeatable, and enhanced gas sensor performance. The phase of TiO2 particles was characterized by Raman and the morphology of the TiO2 particles on the 3D network of SWNTs was analyzed by transmission electron microscope.

The effect of hydrophilic photoacid generator on acid diffusion in chemical amplification resists.

A photoacid generator (PAG) is a component of chemical amplification photoresists (CAR). The most widely used PAG in CAR system is triphenyl onium salt which is well known to one of the best leaving groups from various radiation. Acid diffusion influences resist characteristics in area such as resolution and linewidth control. The structure of the hydrophilic PAG was designed to restrict acid diffusion within the photoresist. Acid amplification was suppressed by the hydroxyl group-acid interaction. Novel PAGs with functional groups were synthesized and characterized. Poly(GMA-co-MMA) was synthesized with a combination of crosslinkable glycidyl methacrylate (GMA) and highly refractive methyl methacrylate (MMA). The synthesized polymers were confirmed by NMR and FT-IR, and their thermal properties were studied using TGA and DSC. The resists were evaluated as a positive type resist for ArF lithography. PAGs exhibited good acid generation efficiency with controlled acid diffusion. We found that the energy latitude property of the photoresist was improved with hydroxyl-PAG.

Synthesis of triphenylsulfonium triflate bound copolymer for electron beam lithography.

Photoacid generator (PAG) has been widely used as a key component in photoresist for high-resolution patterning with high sensitivity. A novel acrylic monomer, triphenylsulfonium salt methyl methacrylate (TPSMA), was synthesized and includes triphenylsulfonium triflate as a PAG. The poly(MMA-co-TPSMA) (PMT) as a polymer-bound PAG was synthesized with methyl methacrylate (MMA) and TPSMA for electron beam lithography. Characterization of PMT was carried out by NMR and FTIR. The molecular weight was analyzed by GPC. Thermal properties were studied using TGA and DSC. Thecharacterization results were in good agreement with corresponding chemical compositions and thermal stability. PMT was subsequently employed in electron beam lithography and its lithographic performance was confirmed by FE-SEM. This PMT was accomplished to improve the lithographic performance including sensitivity, line width roughness (LWR) and resolution. We found that PMT was capable of 20 nm negative tone patterns with better sensitivity than hydrogensilsesquioxane (HSQ) which is a conventional negative tone resist.

Fabrication of cobalt magnetic nanostructures using atomic force microscope lithography.

Cobalt nanopatterns are promising assemblies for patterned magnetic storage applications. The fabrication of cobalt magnetic nanostructures on n-tridecylamine x hydrochloride (TDA x HCl) self-assembled monolayer (SAM) modified silicon surfaces using direct writing atomic force microscope (AFM) lithography for localized electrochemical reduction of cobalt ions was demonstrated. The ions were reduced to form metal nanowires along the direction of the electricfield between the AFM tip and the substrate. In this lithography process, TDA x HCI SAMs play an important role in the lithography process for improving the resolution of cobalt nanopatterns by preventing nonspecific reduction of cobalt ions on the unwritten background. Cobalt nanowires and nanodots with width of 225 +/- 26 nm and diameter of 208 +/- 28 nm were successfully fabricated. Platinium-coated polydimethylsiloxane (PDMS) stamp was used fabricating bulk cobalt structures which can be detected by energy dispersive X-ray spectroscopy for element analysis and the physical and magnetic properties of these cobalt nanopatterns were characterized using AFM and magnetic force microscope.

Growth, solvent effects, and thermal desorption behavior of octylthiocyanate self-assembled monolayers on Au(111).

The growth process, solvent effects, and thermal desorption behavior of octylthiocyanate [OTC, CH(3)(CH(2))(7)S-CN] self-assembled monolayers (SAMs) on Au(111) were characterized by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). To investigate their growth processes, octanethiol [OT, CH(3)(CH(2))(7)S-H] and OTC SAMs were prepared in 0.5 µM ethanol solution at room temperature as a function of immersion time: 10 min, 1 h, 2 h, and 24 h. STM imaging revealed that OT SAMs underwent a phase transition from the liquid phase containing striped-phase domains to the closely packed c(4 × 2) phase. OTC SAMs underwent a different phase transition from the liquid phase containing aggregated molecules to the disordered phase containing striped-phase domains. The adsorption amounts of OTC SAMs formed after immersion for 10 min and 24 h were measured to be 16% and 30% smaller than those of OT SAMs under the same conditions. STM and XPS results show that the growth kinetics of OTC SAMs on Au(111) are much slower than those of OT SAMs. Hexane resulted in OTC SAMs of higher structural quality than ethanol, DMF, or toluene. TDS measurements revealed that the relative desorption intensities of octanethiolate (C8S(+), monomer) and dioctyl disulfide (C8SSC8(+), dimer) to octanethiol (C8SH(+)) fragments for OTC SAMs were much weaker than those of OT SAMs. This is because desorption of monomers and dimers is strongly suppressed by low surface coverage of OTC SAMs, as revealed by STM observations.

Synthesis of novel photoacid generator containing resist polymer for electron beam lithography.

Photoacid generators (PAGs) have been widely used as a key material in the development of novel photoresist materials. One of the important uses of PAGs is found in chemically amplified photoresists (CARs) because of their high photosensitivity and high resolution capability. Triphenylsulfonium salt methacrylate (TPSMA) as the PAG has been bounded in the main polymer backbone. TPSMA was employed for synthesis of terpolymers, poly(MMA-co-tBVPC-co-TPSMA) and poly(tBVPC-co-tBOCPOMI-co-TPSMA) as a positive tone photoresists by free radical polymerization using AIBN. Terpolymers with various ratio of TPSMA, MMA, tBVPC and tBOCOPMI were synthesized and well characterized by FTIR, NMR. Molecular weight distribution was analyzed by GPC. Thermal properties were studied using TGA, DSC which showed thermal stability of terpolymer up to 150 degrees C. We have applied E-beam lithography and KrF lithography in order to demonstrate the effect of the polymer bounded PAG resists. These positive tone resists were successfully applied for fabrication of nano-scale patterns.