Yongping Luo

Nanoporous gold film encapsulating cytochrome c for the fabrication of a H2O2 biosensor

A layer-by-layer route to prepare nanoporous Au film materials on transparent ITO substrates is reported by alternatively assembling Au and Ag nanoparticles through 1,5-pentanedithiol as a cross-linker, followed by that Ag nanoparticles are dissolved at room temperature in HAuCl4 solution. Electron transfer of cytochrome c (cyt. c) - an excellent model for investigation of biomolecules, is greatly facilitated at the nanoporous Au film with electron transfer rate constant (ks) of 3.9s(-1). Meanwhile, cyt. c adsorped onto the nanoporous Au film still maintain its enzymatic activity toward H2O2. On the basis of these experimental results, the cyt. c-nanoporous Au film is exploited to an amperometric biosensor for H2O2 with high selectivity, broad linear range, low detection limit, and long stability.

Plasmon‐Driven Selective Oxidation of Aromatic Alcohols to Aldehydes in Water with Recyclable Pt/TiO2 Nanocomposites

Selective oxidation of alcohols to aldehydes is a key reaction for the synthesis of fine chemicals, since aldehyde derivatives are widely used in the flavoring, confectionary, and beverage industries. Efficient aerobic oxidation of alcohols has usually been facilitated by catalysts such as palladium, platinum, and copper. With the development of photocatalysis, selective photocatalytic oxidation of aromatic alcohols to aldehydes in water has been reported on nanostructured rutile, anatase, and brookite TiO2 under UV irradiation. [3] One of the great challenges in catalysis is to develop new photocatalysts with a high activity response to visible light, which will allow the utilization of sunlight, an abundant and clean low-cost energy source. Recently, the selective oxidation of alcohols in organic solvent was carried out under visible-light irradiation in a catalyst system containing dye-sensitized TiO2 and 2,2,6,6tetramethylpiperidinyloxyl (TEMPO). Herein, we report an alternative strategy for selective oxidation of aromatic alcohols to aldehydes in water with high selectivity and relatively long-term stability based on surface plasmon resonance of platinum nanoparticles deposited onto TiO2 (Pt/TiO2) film under visible-light irradiation at ambient temperature. Surface plasmon resonance of noble metal nanoparticles has been afforded much attention of late, due to their unique properties and their wide applications in multicolor imaging, photovoltaic cells, chemical sensors, and biosensors. Charge separation has also been realized on a metal nanoparticles/TiO2 nanofilm and successfully applied to photovoltaic cells, photocatalysis, and photolithography. However, plasmon-driven selective conversion of alcohols to aldehydes has, to our knowledge, never been reported. Furthermore, compared to the power catalysts, such as the TEMPO-based system, it is much easier for the film catalyst to separate from the system and undergo recycling. In addition, the oxidation has been carried out in water, which is considerably safer, cheaper, and more environmentally friendly than organic solvents. More importantly, the products can be separated by simple decantation, and the catalyst solution can be recycled. TiO2 films with different particle sizes and crystalline forms (anatase or rutile) were prepared from various TiO2 sols by spin coating followed by sintering in air atmosphere. Rutile TiO2 film was fabricated by calcination of anatase TiO2 at high temperature. The size and crystalline form of the TiO2 films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SEM image and XRD pattern of anatase TiO2 STS-21 film sintered at 723 K for 1 h are shown

Plasmon-induced enhancement in analytical performance based on gold nanoparticles deposited on TiO2 film.

This paper demonstrates a novel approach for developing the analytical performance of electrochemical biosensors in which hydrogen peroxide (H(2)O(2)) is selected as a model target, based on surface plasmon resonance of gold nanoparticles (Au NPs) deposited onto a TiO(2) nanoneedle film. Direct electron transfer of cytochrome c (cyt. c) is realized at Au NPs deposited onto a TiO(2) nanoneedle film (Au/TiO(2) film), and both anodic and cathodic currents of the redox reaction at the Au/TiO(2) film upon visible-light irradiation are amplified. Meanwhile, in the presence of oxidized or reduced states of cyt. c, cathodic or anodic photocurrents are generated respectively by the Au/TiO(2) film, suggesting that the amplified anodic and cathodic currents are ascribed to the visible-light excitation. The photocurrent action spectrum obtained at the Au/TiO(2) film in the presence of cyt. c is in a good agreement with the surface plasmon absorption spectrum of Au NPs deposited onto the TiO(2) film, and maximum photocurrent is also consistent with the plasmon absorption peak of Au NPs themselves. It indicates that the enhanced photocurrents generated by visible-light irradiation are attributed to the surface plasmon resonance of Au NPs. On the other hand, experimental results reveal that cyt. c is stably immobilized onto the Au/TiO(2) film and maintains inherent enzymatic activity toward H(2)O(2) even under continuous visible-light illumination. The amplified redox currents of cyt. c produced by surface plasmon resonance of Au NPs, combined with the stability and enzymatic activity of cyt. c confined on the Au/TiO(2) film even after continuous visible-light illumination, subsequently provide the enhanced analytical performance in determination of H(2)O(2). The sensitivity of the present biosensor for H(2)O(2) is 4-fold larger than that obtained without visible-light irradiation, the detection limit is achieved to be 4.5 x 10(-8) M and the dynamic detection linear range extends from 1 x 10(-7) M to 1.2 x 10(-2) M.

Real-Time Electrochemical Monitoring of Cellular H2O2 Integrated with In Situ Selective Cultivation of Living Cells Based on Dual Functional Protein Microarrays at Au−TiO2 Surfaces

This paper demonstrates a novel strategy for site-selective cell adhesion and in situ cultivation of living cells, integrated with real-time monitoring of cellular small biomolecules based on dual functional protein microarrays. The protein microarrays have been produced on the superhydrophobic|philic Au-TiO2 micropatterns, through further modification of L-cysteine (Cys) and followed by successive immobilization of a model protein, cytochrome c (cyt c). Experimental results have revealed that the created cyt c microarrays play dual functions: one is employed as a robust substrate for site-selective cell adhesion and in situ cultivation of living cells, because the protein microarrays exhibit high selectivity and bioaffinity toward cells, as well as long biostability under cell culture condition up to 7 days. Meanwhile, the cyt c microarrays can also serve as sensing elements for hydrogen peroxide (H2O2) due to the inherent enzymatic activity of the heme center in cyt c. Direct electron transfer of cyt c has been enhanced at the Cys-modified Au-TiO2 (Au-TiO2/Cys) microarrays, and the electrochemical behavior can be tuned by varying the width and spacing of the microband arrays. Furthermore, cyt c is stably immobilized on the Au-TiO2/Cys microarrays and maintains its enzymatic activity after confined on the microarrays. Thus, the optimized cyt c microarrays show striking analytical performance for H2O2 determination, e.g., high sensitivity and selectivity, broad linear range from 10(-9) M to 10(-2) M, low detection limit down to 2 nM, and short response time within 5 s. As a result, the excellent analytical properties of the cyt c microarrays, as well as the characteristic of the protein microarrays themselves, including high selectivity, long biostability, and good bioaffinity, opens up a method for selective in situ cultivation of cells integrated with real-time detection of signaling biomolecules such as H2O2 released from living cells, which shows potential for physiological and pathological investigations.

Fabrication of TiO2 and Metal Nanoparticle−Microelectrode Arrays by Photolithography and Site-Selective Photocatalytic Deposition

This paper demonstrates a novel and facile technique for the production of microelectrode arrays based on either TiO2 or metal nanoparticles, which combines photolithography and photocatalytic deposition. A procedure that involves photolithographic selective decomposition of superhydrophobic n-octadecyltriethoxysilane (ODS) has been developed to create superhydrophobic/superhydrophilic TiO2 patterns (i.e., microelectrode arrays based on TiO2 nanoparticles). The generated TiO2 patterns can function as molecular microtemplates, in which elevated metal nanoparticle-based microelectrode arrays are produced by photocatalytic deposition to form microelectrode arrays based on metal nanoparticles. Microscopy and atomic force microscopy have demonstrated that the metal nanoparticles grow site-selectively inside the TiO2 microtemplates. This developed approach can be used to create microelectrode arrays composed by either TiO2 nanoparticles or various metal nanoparticles, such as gold, silver, and platinum, with different patterns. The electrochemical behavior of the as-prepared microelectrode arrays has also been characterized by cyclic voltammetry.

Switching the direction of plasmon-induced photocurrents by cytochrome c at Au-TiO2 nanocomposites

A simple route for controlling the direction of plasmon-induced photocurrents at gold nanoparticles deposited on TiO(2) films is reported for the first time that is based on the electronic state of gold nanoparticles conjugated to redox-active cytochrome c and plasmon-enhanced electron exchange.