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PubMed2005

Hydrogen bonding effects on the surface structure and photoelectrochemical properties of nanostructured SnO2 electrodes modified with porphyrin and fullerene composites.

Hydrogen bonding effects on surface structure, photophysical properties, and photoelectrochemistry have been examined in a mixed film of porphyrin and fullerene composites with and without hydrogen bonding on indium tin oxide and nanostructured SnO2 electrodes. The nanostructured SnO2 electrodes modified with the mixed films of porphyrin and fullerene composites with hydrogen bonding exhibited efficient photocurrent generation compared to the reference systems without hydrogen bonding. Atomic force microscopy, infrared reflection absorption, and ultraviolet-visible absorption spectroscopies and time-resolved fluorescence lifetime and transient absorption spectroscopic measurements disclosed the relationship between the surface structure and photophysical and photoelectrochemical properties relating to the formation of hydrogen bonding between the porphyrins and/or the C60 moieties in the films on the electrode surface. These results show that hydrogen bonding is a highly promising methodology for the fabrication of donor and acceptor composites on nanostructured semiconducting electrodes, which exhibit high photoelectrochemical properties.

Electrochemistry↗
PubMed2005

Self-assembly of active IrO2 colloid catalyst on an ITO electrode for efficient electrochemical water oxidation.

Active catalysts for water oxidation to evolve O(2) are required for the construction of artificial photosynthetic devices that are expected to be promising energy-providing systems in the future. The citrate-stabilized IrO(2) colloid was self-assembled onto an indium tin oxide (ITO) electrode to form a monolayer of the colloidal IrO(2) particles when it was dipped in the colloid solution. The self-assembly could be achieved by a chemical interaction between carboxylate groups on the citrate stabilizer and hydroxyl groups on the ITO surface to form ester bonds. Efficient electrocatalysis for water oxidation was demonstrated using the electrode modified by the self-assembled IrO(2) colloid to yield the highest turnover frequency ((2.3-2.5) x 10(4) h(-1)) of IrO(2) in the hitherto-reported catalysts for electrochemical water oxidation.

Catalysis↗
PubMed2006

Improved performance in dye-sensitized solar cells employing TiO2 photoelectrodes coated with metal hydroxides.

The performance of dye-sensitized solar cells (DSCs) was compared before and after processing the TiO(2) electrodes by minute-order electrochemical reactions with metal nitrates, where the metals were Mg, Zn, Al, and La, in 2-propanol. An overcoating of metal hydroxide was formed without the need for a sintering process, and magnesium hydroxide was found to give the largest improvement in photovoltage, fill factor, and eventually overall conversion efficiency of the DSCs. To analyze the nature of the improvement, the diffusion coefficient (D) and electron lifetime (tau) were determined. While little influence of overcoating on D was seen, a correlation between the increase in tau and V(oc) was observed for the metals examined here. The remarkable improvement in the electron lifetime of the DSCs suggests that an overcoating with magnesium hydroxide species function as the blocking layers at the fluorine-doped tin oxide and TiO(2) interfaces, thus contributing to the suppression of electron leakage, i.e., recombination processes between unidirectional transporting electrons and poly-iodides such as tri-iodide in the processed TiO(2) photoelectrode systems. The increase in V(oc) can be explained by the increased electron density caused by the increase in electron lifetime.

2-Propanol↗
PubMed2006

Photoinduced thermal copper reduction onto gold nanocrystals under potentiostatic control.

We study the photoreduction of adsorbed copper ions onto Au nanoparticles, on an indium tin oxide (ITO) electrode in an aqueous electrochemical cell, as a function of applied voltage and laser intensity. The photocurrent is a nonlinear function of laser intensity and increases sharply with cathodic voltage in the underpotential deposition region. The photoreduction is attributed to laser heating of the Au nanoparticles rather than "hot electron" processes. Numerical simulation of the Butler-Volmer kinetic equation using experimental parameters predicts a several orders of magnitude increase in current for a temperature rise of a few Kelvin.

Adsorption↗
PubMed2006

Organized assemblies of single wall carbon nanotubes and porphyrin for photochemical solar cells: charge injection from excited porphyrin into single-walled carbon nanotubes.

Photochemical solar cells have been constructed from organized assemblies of single-walled carbon nanotubes (SWCNT) and protonated porphyrin on nanostructured SnO2 electrodes. The protonated form of porphyrin (H4P2+) and SWCNT composites form 0.5-3.0 microm-sized rodlike structures and they can be assembled onto nanostructured SnO2 films [optically transparent electrode OTE/SnO2] by an electrophoretic deposition method. These organized assemblies are photoactive and absorb strongly in the entire visible region. The incident photon to photocurrent efficiency (IPCE) of OTE/SnO2/SWCNT-H4P2+ is approximately 13% at an applied potential of 0.2 V versus saturated calomel electrode. Femtosecond pump-probe spectroscopy experiments confirm the decay of the excited porphyrin in the SWCNT-H4P2+ assembly as it injects electrons into SWCNT. The dual role of SWCNT in promoting photoinduced charge separation and facilitating charge transport is presented.

Electrodes↗
PubMed2005

Polypeptide-mediated silica growth on indium tin oxide surfaces.

Herein, we describe the formation of silica structures on indium tin oxide (ITO) surfaces using poly-L-lysine (PLL) to template the condensation of silicic acid. Precisely controlled electrostatic fields were used to preposition PLL onto ITO surfaces. Subsequent polypeptide-mediated silicification resulted in the formation of silica with concentration gradients that followed the pattern of the externally applied electrostatic field used in the deposition of the PLL. The resulting silica structures were securely attached to the ITO surface. The technique described here offers an inexpensive and rapid method for the deposition of polypeptides on surfaces.

Biomimetics↗
PubMed2005

Chemical control of electrode functionalization for detection of DNA hybridization by electrochemical impedance spectroscopy.

We report sensitive label-free detection of DNA oligonucleotide sequences using ac impedance measurements. The surface attachment chemistry is critical, and using mixed self-assembled monolayers on a gold electrode results in much better performance than homogeneous self-assembled monolayers. Contrary to expectations, binding of the target sequence reduces rather than increases the charge transfer resistance. Similar behavior is observed on indium tin oxide electrodes, and we ascribe it to the hydrophilicity and rigidity of the DNA duplex that cause it to reside further from the electrode surface and facilitate the approach of negatively charged redox moieties to the interface.

Base Sequence↗
PubMed2005

Photoinduced electron transfer in self-assembled monolayers of porphyrin-fullerene dyads on ITO.

Two porphyrin-fullerene dyads were synthesized to form self-assembled monolayers (SAMs) on indium-tin oxide (ITO) electrode, with either ITO-porphyrin-fullerene or ITO-fullerene-porphyrin orientations. The dyads contain two linkers for connecting the porphyrin and fullerene moieties and enforcing them essentially to similar geometries of the donor-acceptor pair, and two linkers to ensure the attachment of the dyads to the ITO surface with two desired opposite orientations. The transient photovoltage responses (Maxwell displacement charge) were measured for the dyad films covered by insulating LB films, thus ensuring that the dyads interact only with the ITO electrode. The direction of the electron transfer was from the photoexcited dyad to ITO independent of the dyad orientation. The response amplitude for the ITO-fullerene-porphyrin structure, where the primary intramolecular electron-transfer direction coincides with the direction of the final electron transfer from the dyad to ITO, was 25 times stronger than that for the opposite ITO-porphyrin-fullerene orientation of the dyad. Static photocurrent measurements in a liquid electrochemical cell, however, show only a minor orientation effect, indicating that the photocurrent generation is controlled by the processes at the SAM-liquid interface.

Electrodes↗
PubMed2005

Porous tin oxide nanostructured microspheres for sensor applications.

We have sought to enhance the sensitivity of conductometric gas microsensors through the design and fabrication of porous, three-dimensional tin oxide nanoparticle structures. Electrostatically controlled layer-by-layer processing in aqueous solutions was used to decorate sacrificial latex microspheres with Sb:SnO2 nanoparticles. To evaluate their sensing performance, these structures were then deposited as films, via micropipetting, on MEMS micro-hot-plate platforms with interdigitated electrodes. Prior to gas testing, rapid heating of the micro-hot-plates was used to remove the sacrificial latex templates, thereby revealing a 3-D structure composed of interconnected spherical tin oxide nanoparticle shells with porous ultrathin walls. Changes in film conductance, caused by exposure to test gases (methanol, carbon monoxide, benzene, water) in a dry air background, were measured at different temperatures. Hollow nanoparticle microsphere films exhibited partial selectivity for these different gases, good dynamic range at different temperatures and gas concentrations, and good repeatability and stability over long runs. These films also yielded approximately 3-fold and 5-fold increases in sensitivity to methanol when compared to SnO2 polycrystalline chemical vapor deposition films and Sb:SnO2 microporous nanoparticle films, respectively. Gains in sensitivity are attributed to the multiscale porous architecture of the hollow microsphere films. This architecture promotes gas diffusion and increases the active surface area.

Electrodes↗
PubMed2005

Layer-by-layer assembly of poly(ethyleneimine) and plasmid DNA onto transparent indium-tin oxide electrodes for temporally and spatially specific gene transfer.

The layer-by-layer assembly technique was used to adsorb alternately poly(ethyleneimine) and plasmid DNA onto the surface of a transparent electrode made of indium-tin oxide. The surface with adsorbed poly(ethyleneimine) and DNA was characterized by X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and contact angle measurements. These analyses revealed that the alternate adsorption process generated a multilayered assembly of cationic poly(ethyleneimine) and anionic DNA. For the spatially and temporally specific gene transfer, cells were cultured on the plasmid-loaded electrode and then a short electric pulse was applied to the cell-electrode system. It was shown that, upon electric pulsing, the plasmid was released from the electrode and transferred into the cells, resulting in efficient gene expression even in primary cultured cells. Transfection could be effected for hippocampal neurons after 3-day culture on the plasmid-loaded electrode, which indicated the feasibility of selecting the time of transfection. Our results also showed that electroporation could be performed in a spatially specific manner by using a plasmid-arrayed electrode, demonstrating the feasibility of the method for the fabrication of transfected cell microarrays.

Animals↗
PubMed2006

Self-assembly of tin oxide nanoparticles: localized percolating network formation in polymer matrix.

A novel method to prepare transparent antistatic films by trapping nanoparticles in thin surface layers is proposed, and high performance of the product is demonstrated. Coating solutions consisting of surface-active antimony-doped tin oxide (ATO) nanoparticles, an organic solvent mixture of high affinity with poly(methyl methacrylate) substrate, and an ultraviolet curable resin are used for the film formation. Antistatic property of the layer is obtained at ATO concentrations above the critical concentration for percolation. A scaling analysis of the data shows that the critical concentration (0.004 volume fraction) is extremely low as compared to the value predicted by the percolation theory for randomly packed systems as well as the values in ever developed composite films filled with ATO particles. Microscopic observation of the deposited layers indicates that percolating clusters of ATO particles are localized on the layer surfaces. The excellent electrical and optical properties of the layer are attributed to the characteristic microstructure.

Antimony↗
PubMed2006

Cathodic electrodeposition of mixed molybdenum tungsten oxides from peroxo-polymolybdotungstate solutions.

Mixed molybdenum tungsten trioxide films of varying stoichiometry (MoxW1 - xO3, 0 < x < 1) were prepared by cathodic electrodeposition on indium tin oxide (ITO)-coated glass substrates from aqueous peroxo-polymolybdotungstate solutions. Electrochemical quartz crystal microbalance (EQCM), cyclic voltammetry, and chronocoulometry were used to gain insight into the electrodeposition mechanism. The compositional and structural properties were characterized for MoxW1 - xO3 films deposited at intermediate potentials (-0.35 V vs Ag/AgCl) and sintered at 250 degrees C using energy-dispersive spectroscopy, X-ray diffraction, and Raman spectroscopy. These studies reveal that films consist of homogeneously mixed MoxW1 - xO3, with an enriched Mo content ranging in composition from 0.4 < x < 0.7 depending upon the mol % Mo present in the deposition solution. Chronoamperometry and spectroelectrochemical measurements were conducted to estimate lithium ion diffusion coefficients and coloration efficiencies for the mixed metal oxide films in 1 M LiClO4/propylene carbonate. The subtle interplay between structural and compositional properties due to the uniform mixing of Mo and W oxide components shows that electrochromic and lithium ion transport properties are moderately enhanced relative to those of single-component WO3 and MoO3 and demonstrate improved structural stability over pure MoO3 polymorphs during electrochemical cycling.

Cations↗
PubMed2006

Functionalization of indium tin oxide.

The preparation and functionalization of ITO surfaces has been studied using primarily X-ray photoemission spectroscopy and infrared reflection-absorption spectroscopy (IRRAS) and the reagents n-hexylamine and n-octyltrimethoxysilane (OTMS). Particular attention has been paid to characterization of the surfaces both before and after functionalization. Surfaces cleaned by ultraviolet (UV)/ozone treatment and subsequently exposed to room air have approximately 0.5-0.8 monolayers (ML) of adsorbed impurity C. Most is in the form of aliphatic species, but as much as one-half is partially oxidized and consists of C-OH, C-O-C, and/or >C=O groups. The coverage of these species can be reduced by cleaning in organic solvents prior to UV/ozone treatment. The OH coverage on the ITO surfaces studied here is relatively small (approximately 1.0 OH nm-2), based on the Si coverage after reaction with OTMS. A satellite feature in the O 1s XPS spectrum, often suggested to be a quantitative measure of adsorbed OH, receives a significant contribution from sources not directly related to hydroxylated ITO. n-Hexylamine adsorbs, at a saturation coverage of approximately 0.08 ML, via a Lewis acid-base interaction. The particular acid site has not been conclusively identified, but it is speculated that surface Sn sites may be involved. For OTMS, a saturation coverage of about 0.21 ML is found, and the C/Si atom ratios suggest that some displacement of preadsorbed organic impurities occurs during adsorption. The alkyl chain of adsorbed OTMS is disordered, with no preferred stereoisomer. However, the chain appears to lie mainly parallel to the surface with the plane defined by the terminal CH3-CH2-CH2- segment oriented essentially perpendicular to the surface.

Adsorption↗
PubMed2005

Electrochemical tuning of silver nanoparticles fabricated by nanosphere lithography.

An electrochemical method is developed to quantitatively modify and spectroscopically monitor the size and shape of Ag nanotriangles fabricated by nanosphere lithography (NSL) on an indium tin oxide (ITO) electrode surface. AFM and SEM results demonstrate that the preferential order of electrochemical oxidation for a nanotriangle is, surprisingly, bottom edges first, then triangular tips, then out-of-plane height.

Crystallization↗
PubMed2006

Toward the nanoscopic "electronic nose": hydrogen vs carbon monoxide discrimination with an array of individual metal oxide nano- and mesowire sensors.

The array of chemiresistors made of individual pristine SnO2, surface doped (Ni)-SnO2 nanowires, and TiO2 and In2O3 mesoscopic whiskers was fabricated on a Si/SiO2 wafer. Their conductance was measured under pulses of H2 and CO reducing gases in oxygen as background gas. The nanostructures were shown to be n-type semiconductors possessing high sensitivity to the target gases. Following the "electronic nose" concept, correlation analysis of response of three-chemiresistor array is shown to be sufficient to discriminate between H2 and CO signals.

Biosensing Techniques↗
PubMed2000

Synthetic studies on the trans-chlorocyclopropane dienyne side chain of callipeltoside A.

[structure] Enantiomerically enriched trans-chlorocyclopropanemethanol was obtained by lipase kinetic resolution of dichlorocyclopropanemethanol 3, followed by reduction. The sp-sp(2) bond of the trans-chlorocyclopropane dienyne side chain of callipeltoside A was constructed via a Stille coupling reaction of 1, 1-dibromo-1-alkene 7 and a vinylstannane in a highly dipolar solvent capable of promoting HBr elimination to give internal alkynes.

Animals↗
PubMed2001

Double allylation reactions of (2-azaallyl)stannanes: synthesis of N,N-bis(3-butenyl)amines and their conversion to 2,3,6,7-tetrahydroazepines via ring-closing metathesis.

[reaction in text] Treatment of (2-azaallyl)stannanes (i) with 2.2 equiv of allylmagnesium bromide afforded good yields of N,N-bis(3-butenyl)amines derivatives (ii), which were subjected to ring-closing metathesis to afford 2,3,6,7-tetrahydroazepines (iii). Thus, (2-azaallyl)stannanes are the synthetic equivalents of amine alpha,alpha'-dications.

Alkenes↗
PubMed2001

Highly diastereoselective synthesis of propargylic 1,2-anti-diol derivatives using alpha-alkoxypropargylstannanes.

Propargylic 1,2-anti-diol derivatives 2 and 10 are prepared in high yield and excellent diastereoselectivity by addition of alpha-alkoxypropargylstannanes 4a and 4b to aldehydes in the presence of BuSnCl(3). We also introduce the use of KF on Celite as a convenient and mild reagent for removal of the organotin waste products of these reactions. Reaction: see text.

Aldehydes↗