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.

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.

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.

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.

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.

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.

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.

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.

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.

Biophysical characterization of the molecular orientation of an antibody-immobilized layer using secondary ion mass spectrometry.

The molecular orientation of antibody layers formed on separate solid matrices (e.g., gold-coated glass substrate) was characterized by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS) in static mode. For comparison, three different antibody species, IgG, F(ab')(2), and Fab, were prepared, biotinylated in random and site-directed fashions, and immobilized on distinct streptavidin-coated surfaces. ToF-SIMS analyses of each antibody layer revealed that the secondary ion intensity peaks measured at the mass-to-charge (m/z) ratio 253, 325, and 647 were unique to the site-directly immobilized antibodies. The ions in the three peaks were detected neither from the streptavidin layer nor from the randomly prepared antibody, indicating that the insolubilized antibody layers constructed in the two different manners had distinct molecular arrangements. The antibody preparations were further tested for their binding characteristics in sandwich-type immunoassays, which showed that the site-directed antibodies consistently enhanced the detection capability comparing to those randomly prepared. Based on the analytical results of both the ToF-SIMS analysis and sandwich-type immunoassays, the site-directed antibody species were immobilized on the surfaces in a more orientated manner, with their antigen binding sites exposed to the bulk solution, than when random immobilization was used.

Modification of silicon substrate using low-energy proton beam for selective growth of CNTs.

A 3 keV low-energy proton beam was used to irradiate a silicon substrate for selective modification. The water contact angle measurement, chemical etching test with HF and the auger electron spectroscopy were used to investigate the chemical properties and the material composition of the proton beam-irradiated silicon substrate. The proton beam-irradiated silicon substrate was covered with a silicon oxide layer of about 60-70 angstroms due to the incorporation of oxygen molecules after exposure to ambient air. The silicon oxide layer produced by the proton beam was highly resistant to HF treatment which typically used to remove the silicon oxide on a substrate, and the surface of it was more hydrophilic than the native silicon oxide removed silicon surface with Si-H surface group. For the selective growth of carbon nanotubes (CNTs), the silicon oxide pattern was easily fabricated via proton beam irradiation when the silicon substrate was covered with a shadow mask. The Fe-Mo bimetallic catalysts for the growth of CNTs were adsorbed onto the silicon oxide layer, which is more hydrophilic than the silicon surface. The CNTs were grown on the patterned substrate using a chemical vapor deposition method, and it was confirmed by scanning electron microscopy.

Electrical impedance properties of carbon nanotube composite electrodes for chemical and biosensor.

Electrical impedance properties of different type of carbon nanotubes based bulk electrodes have been investigated to develop chemical and biosensors. The bulk composite electrodes were fabricated with single-wall and multi-wall carbon nanotubes involving ionic conducting host polymer, Nafion, by using traditional solution-casting techniques. Under the various amounts of buffer solution, resistance and capacitance of the electrodes were measured with LCR meter and their characteristics due to ionic conducting host polymer were investigated by means of electrokinetic analysis. The capacitance values showed drastic change while the resistances only changed within few percent ranges. Electrical impedance measurement provided rapid and simple sensing mechanism to develop chemical sensor and biosensors with bulk nano electrodes.

The fabrication of polyaniline/single-walled carbon nanotube fibers containing a highly-oriented filler.

Highly uniform composite nanofibers composed of well-oriented single-walled carbon nanotubes (SWCNTs) wrapped in a conducting polymer have been fabricated using electrospinning. Water-soluble polyaniline (WS-PANI) was used as a conducting material to improve the processability during electrospinning. The WS-PANI formed a homogeneous dispersion with the SWCNTs and poly(vinyl alcohol), and good compatibility of the WS-PANI with the SWCNTs was demonstrated by data showing interactions between two components and the wrapping of the SWCNTs by the WS-PANI. Through transmission electron microscopy, atomic force microscopy, and polarized Raman spectroscopy, we confirmed that the WS-PANI plays an important role as a conducting polymer matrix to achieve aligned SWCNTs in composite nanofibers and to form uniform nanofibers.

Direct nanofabrication of copper on silicon substrate by electrochemical atomic force microscope lithography.

The electrochemical reaction by applying an electrical bias between an atomic force microscope (AFM) tip and a substrate was used to directly fabricate desired copper patterns. The negative sample bias could strongly reduce copper at the point localized by an AFM tip but not oxidize silicon. The mixture solution of Cu(NO3)2 and poly(sodium 4-styrenesulfonate) which are highly soluble in water was used to form a conductive copper ion film. The arrayed dots and line patterns were fabricated by electrical exposure at regular steps and continuous bias, respectively. This technique demonstrated the fabrication of copper patterns by using the electrochemical reduction by AFM lithography.

Two-dimensional ordering of benzenethiol self-assembled monolayers guided by displacement of cyclohexanethiols on Au(111).

Although the adsorption of benzenethiols (BT) on Au(111) usually leads to the formation of disordered phases, we demonstrate here that the displacement of preadsorbed cyclohexanethiol self-assembled monolayers (SAMs) on Au(111) by BT molecules can be a successful approach to obtain two-dimensional BT SAMs with long-range ordered domains.

Fabrication of patterned single-walled carbon nanotube films using electrophoretic deposition.

Thin films of chemically functionalized single-walled carbon nanotubes (SWNTs) were fabricated by using a direct current (dc) electrophoretic deposition method. SWNTs were shortened and then functionalized with acid chloride group to combine with the amine group-terminated gold substrate. Silica nanospheres with a diameter of about 190 nm were arrayed on gold substrate to pattern a thin SWNT film. Periodically patterned SWNT film was eventually produced and would be used in potential applications like electron emitters and large surface area electrodes.

Characterization of mixed self-assembled monolayers for immobilization of streptavidin using chemical force microscopy.

Mixed self-assembled monolayers (SAMs) to immobilize streptavidin on a gold surface were investigated by measuring the pull-off force between an AFM tip and a biotin-modified surface using CFM. Biotin-LC-NHS was modified on SAMs prepared from a mixed solution of cystamine and MEOH. Increased pull-off forces between the AFM tip and the surface were observed with an increased cystamine mole fraction in the solution. Streptavidin was immobilized onto biotin-LC-NHS modified mixed SAMs and analyzed by tapping AFM. Also, the formation of mixed SAMs containing MUOH and MBDA was confirmed using CFM. The measured pull-off forces on the only MBDA surface were larger than those on the surface with MUOH. These results can be applied to determine an optimal mixing ratio of MUOH and MBDA SAMs that reduces non-specific streptavidin binding onto a surface.

Effect of solvent and dopant on poly(3,4-ethylenedioxythiophene) thin films by atomic force microscope lithography.

AMF anodization lithography was performed on organic thin films with conducting polymers which is poly(3,4-ethylenedioxythiophene). The conductivity of PEDOT thin films was changed by different dopants and organic solvents. Two different dopants are poly(4-styrenesulfonate) and di(2-ethylhexyl)-sulfosuccinate. Also, DMF and IPA were used to prepare the PEDOT thin films doped with PSS and DEHS on silicon surface. The conductivities of these PEDOT variants were compared by obtaining their I-V curves between tip and thin films using AFM. Silicon oxide nanopatterns with higher aspect ratios can be obtained from the films with higher conductivity.

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.