A novel hydrogen peroxide biosensor based on the immobilization of hemoglobin on three-dimensionally ordered macroporous (3DOM) gold-nanoparticle-doped titanium dioxide (GTD) film

The three-dimensionally ordered macroporous gold-nanoparticle-doped titanium dioxide (3DOM GTD) film was modified on the indium-tin oxide (ITO) electrode surface. Hemoglobin (Hb) has been successfully immobilized on the 3DOM GTD film and the fabrication process was characterized by Raman and UV-vis spectra. The results indicated that the Hb immobilized on the film retained its biological activity and the secondary structure of Hb was not destroyed. The direct electrochemistry and electrocatalysis of Hb immobilized on this film have been investigated. The Hb/3DOM GTD/ITO electrode exhibited two couples of redox peaks corresponding to the Hb intercalated in the mesopores and adsorbed on the external surface of the film with the formal potential of -0.20 and -0.48 V in 0.1M PBS (pH7.0), respectively. The Hb/3DOM GTD/ITO electrode exhibits an excellent eletrocatalytic activity, a wide linear range for H(2)O(2) from 5.0 μM to 1.0mM with a limit of detection of 0.6μM, high sensitivity (144.5 μA mM(-1)), good stability and reproducibility. Compared with the TiO(2) nanoneedles modified electrode, the GTD modified electrode has higher sensitivity and response peak current. The 3DOM GTD provided a good matrix for bioactive molecules immobilization, suggesting it has the potential use in the fields of H(2)O(2) biosensors.     

Molecularly imprinted polyaniline film for ascorbic acid detection

Molecularly imprinted polyaniline (PANI) film (～ 100 nm thick) has been electrochemically fabricated onto indium-tin-oxide (ITO) coated glass plate using ascorbic acid (AA) as template molecule. Fourier transform infra-red spectroscopy, scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry (DPV) studies indicate the presence of AA in PANI matrix, which also acts as a dopant for PANI. Further, the AA selective molecularly imprinted PANI electrode (AA-MI-PANI/ITO) has been developed via over-oxidation of AA doped PANI electrode which leads to the removal of AA moieties from PANI film. The response studies using DPV technique have revealed that this molecularly imprinted AA-MI-PANI/ITO electrode can detect AA in the range of 0.05-0.4 mM with detection limit of 0.018 mM and sensitivity of 1.2 × 10(-5) AmM(-1). Interestingly, this AA-MI-PANI/ITO electrode shows excellent reusability, selectivity and stability.     

A sputtered thin film of nanostructured Ni/Pt/Ti on Al2O3 substrate for ethanol sensing

A novel thin film ethanol sensor using sputtered Ni/Pt/Ti on an Al2O3 substrate as the working electrode in an alkaline solution was developed. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the nanostructure of nickel films. Sputtering deposition conditions for maximum catalytic efficiency, electrode selectivity, and reproducibility were discussed. The results showed that ethanol oxidation was more efficient on the sputtered Ni/Pt/Ti on an Al2O3 substrate electrode than that on the conventional nickel electrode. The optimal operating conditions to generate the sputtered Ni/Pt/Ti on the Al2O3 substrate electrode were: 45 min of Ni sputtering deposition time, and 50 W of Ni sputtering power. The results also indicated that the response time of the prepared ethanol sensor is 27 s and the best sensitivity is 3.08 microA microM(-1) cm(-2).     

Iron oxide nanoparticles-chitosan composite based glucose biosensor

Iron oxide (Fe(3)O(4)) nanoparticles prepared using co-precipitation method have been dispersed in chitosan (CH) solution to fabricate nanocomposite film on indium-tin oxide (ITO) glass plate. Glucose oxidase (GOx) has been immobilized onto this CH-Fe(3)O(4) nanocomposite film via physical adsorption. The size of the Fe(3)O(4) nanoparticles estimated using X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) has been found to be approximately 22 nm. The CH-Fe(3)O(4) nanocomposite film and GOx/CH-Fe(3)O(4)/ITO bioelectrode have been characterized using UV-visible and Fourier transform infrared (FTIR) spectroscopic and scanning electron microscopy (SEM) techniques, respectively. This GOx/CH-Fe(3)O(4)/ITO nanocomposite bioelectrode has response time of 5s, linearity as 10-400 mgdL(-1) of glucose, sensitivity as 9.3 microA/(mgdLcm(2)) and shelf life of about 8 weeks under refrigerated conditions. The value of Michaelis-Menten (K(m)) constant obtained as 0.141 mM indicates high affinity of immobilized GOx towards the substrate (glucose).     

High‐Performance Ta2O5/Al‐Doped Ag Electrode for Resonant Light Harvesting in Efficient Organic Solar Cells

A efficient indium tin oxide (ITO)‐free transparent electrode based on an improved Ag film is designed by introducing small amount of Al during co‐deposition, producing ultrathin and smooth Ag film with low loss. A transparent electrode as thin as 4 nm is achieved by depositing the film on top of Ta₂O₅ layer, and organic solar cells based on such ultrathin electrode are built, producing power conversion efficiency over 7%. The device efficiency can be optimized by simply tuning Ta₂O₅ layer thickness external to the organic photovoltaic (OPV) structure to create an optical cavity resonance inside the photoactive layer. Therefore Ta₂O₅/Al‐doped Ag films function as a high‐performance electrode with high transparency, low resistance, improved photon management capability and mechanical flexibility.     

电极介导的菌紫质干膜微分光电流响应的整流性质

在长方形光脉冲光照下,菌紫质(bacteriorhodopsin,BR)干膜组装成夹层光电池具有微分光电流响应．在氧化铟锡(ITO)导电玻璃/BR膜/封口膜/不锈钢形成的干膜电池下可观察到整流特性,而在不锈钢/BR膜/封口膜/ITO导电玻璃形成的干膜电池下则观察不到整流特性,这说明是电极介导的整流．平衡电压测定表明：工作电极/BR膜表面与对电极/BR膜表面有不同的性质,电极的界面效应控制了BR的取向．酸与碱产生的瞬间电流极性也证实了电极整流行为的存在．这些结果将有助于了解BR膜的微分光电响应．     

Bioelectronic device consisting of cytochrome c/poly-L-aspartic acid adsorbed hetero-Langmuir-Blodgett films

A bioelectronic device consisting of protein-adsorbed hetero-Langmuir-Blodgett (LB) films was investigated. Four kinds of functional molecules, cytochrome c, viologen, flavin, and ferrocene, were used as a secondary electron acceptor (A2), a first electron acceptor (A1), a sensitizer (S), and an electron donor (D), respectively. To fabricate the cytochrome c adsorbed hetero-LB film, poly-L-aspartic acid was used as the bridging molecule. The hetero-LB film was fabricated by subsequently depositing ferrocene, flavin, and viologen onto the pretreated ITO glass. Cytochrome c-adsorbed hetero-LB films were prepared by the adsorption of cytochrome c onto the poly-L-aspartic acid treated-LB films by intermolecular electrostatic attraction. Finally, the MIM (metal/insulator/metal) structured molecular device was constructed by depositing aluminum onto the surface of the cytochrome c-adsorbed hetero-LB films. Hetero-LB films were analyzed by Atomic Force Microscopy (AFM), and cytochrome c adsorption onto the films confirmed. The photoswitching function was achieved and the photoinduced unidirectional flow was in accordance with the rectifying characteristics of the molecular device. The direction of energy flow was in accordance with the energy level profile across molecular films. Based on the measurement of the transient photocurrent of the molecular device efficient directional flow of photocurrent through the redox potential difference was observed. The photodiode characteristics of the proposed bio-electronic device were verified and the proposed molecular array mimicking the photosynthetic reaction center could be usefully applied as a model system for the development of the bio-molecular photodiode.     

Amperometric biosensor based on coentrapment of enzyme and mediator by gold nanoparticles on indium-tin oxide electrode

A disposable pseudo-mediatorless amperometric biosensor has been fabricated for the determination of hydrogen peroxide (H2O2). In the current study, an indium-tin oxide (ITO) electrode was modified with thiol functional group by (3-mercaptopropyl)trimethoxysilane. The stable nano-Au-SH monolayer (AuS) was then prepared through covalent linking of gold nanoparticles and thiol groups on the surface of the ITO. The horseradish peroxidase (HRP) and tetramethyl benzidine (TMB) were finally coentrapped by the colloidal gold nanoparticles. The immobilized TMB was used as an electron transfer mediator that displayed a surface-controlled electrode process at a scan rate of less than 50mV/s. The biosensor was characterized by photometric and electrochemical measurements. The results showed that the prepared AuS monolayer not only could steadily immobilize HRP but also could efficiently retain HRP bioactivity. Parameters affecting the performance of the biosensor, including the concentrations of the immobilized TMB and HRP, the pH value, and the reaction temperature, were optimized. Under the optimized experimental conditions, H(2)O(2) could be determined in a linear calibration range from 0.005 to 1.5mM with a correlation coefficient of 0.998 (n=14) and a detection limit of 1microM at a signal/noise ratio of 3. The proposed method provides a new alternative to develop low-cost biosensors by using ITO film electrodes from industrial mass production.     

Rectified photocurrent of molecular photodiode consisting of cytochrome c/GFP hetero thin films.

Photoinduced electron transfer in the molecular electronic device consisting of protein-adsorbed hetero Langmuir–Blodgett (LB) film was investigated. Three kinds of functional molecules, cytochrome c, viologen, and green fluorescent protein (GFP) were used as an electron acceptor, a mediator, and a sensitizer, respectively. The hetero-LB film was fabricated by subsequently depositing cytochrome c and viologen onto the pretreated ITO or quartz glass. GFP adsorbed hetero-LB films were prepared by soaking the hetero-LB films into the buffer solution containing GFP. The MIM (metal/insulator/metal) structured molecular device was constructed by depositing aluminum onto the surface of the GFP-adsorbed hetero LB films. Due to the excitation by irradiation with a 460 nm monochromic light source, the photoinduced unidirectional flow of electrons in the MIM device could be achieved and was detected as photocurrents. The photoswitching function was achieved and the rectifying characteristic was observed in the molecular device. Based on the measurement of transient photocurrent of molecular device, the unidirectional flow of electrons was verified.     

Disposable biosensor based on enzyme immobilized on Au-chitosan-modified indium tin oxide electrode with flow injection amperometric analysis

Indium tin oxide (ITO) electrode is used to fabricate a novel disposable biosensor combined with flow injection analysis for the rapid determination of H2O2. The biosensor is prepared by entrapping horseradish peroxidase (HRP) enzyme in colloidal gold nanoparticle-modified chitosan membrane (Au-chitosan) to modify the ITO electrode. The biosensor is characterized by scanning electron microscope, atomic force microscope, and electrochemical methods. Parameters affecting the performance of the biosensor, including concentrations of o-phenylenediamine (OPD) and pH of substrate solution, were optimized. Under the optimal experimental conditions, H2O2 could be determined in the linear calibration range from 0.01 to 0.5 mM with a correlation coefficient of 0.997 (n=8). The amperometric response of the biosensor did not show an obvious decrease after the substrates were injected continuously 34 times into the flow cell. The prepared biosensor not only is economic and disposable, due to the low-cost ITO film electrode obtained from industrial mass production, but also is capable with good detection precision, acceptable accuracy, and storage stability for the fabrication in batch.     

Nanowire‐Based Three‐Dimensional Transparent Conducting Oxide Electrodes for Extremely Fast Charge Collection

A 3D transparent conducting oxide (3D‐TCO) has been fabricated by growing Sn‐doped indium oxide (ITO) nanowire arrays on glass substrates via a vapor transport method. The 3D TCO charge‐collection properties have been compared to those of conventional two‐dimensional TCO (2D‐TCO) thin films. For use as a photoelectrode in dye‐sensitized solar cells, ITO‐TiO₂ core‐shell nanowire arrays were prepared by depositing a 45 nm‐thick mesoporous TiO₂ shell layer consisting of ～6 nm anatase nanoparticles using TiCl₄ treatments. Dye‐sensitized solar cells fabricated using these ITO‐TiO₂ core‐shell nanowire arrays show extremely fast charge collection owing to the shorter electron paths across the 45 nm‐thick TiO₂ shell compared to the 2D TCO. Interestingly, the charge‐collection time does not increase with the overall electrode thickness, which is counterintuitive to conventional diffusion models. This result implies that, in principle, maximum light harvesting can be achieved without hindering the charge collection. The proposed new 3D TCO should also be attractive for other photovoltaic applications where the active layer thickness is limited by poor charge collection.     

Rectified photocurrent of molecular photodiode consisting of cytochrome c/GFP hetero thin films

Photoinduced electron transfer in the molecular electronic device consisting of protein-adsorbed hetero Langmuir–Blodgett (LB) film was investigated. Three kinds of functional molecules, cytochrome c, viologen, and green fluorescent protein (GFP) were used as an electron acceptor, a mediator, and a sensitizer, respectively. The hetero-LB film was fabricated by subsequently depositing cytochrome c and viologen onto the pretreated ITO or quartz glass. GFP adsorbed hetero-LB films were prepared by soaking the hetero-LB films into the buffer solution containing GFP. The MIM (metal/insulator/metal) structured molecular device was constructed by depositing aluminum onto the surface of the GFP-adsorbed hetero LB films. Due to the excitation by irradiation with a 460 nm monochromic light source, the photoinduced unidirectional flow of electrons in the MIM device could be achieved and was detected as photocurrents. The photoswitching function was achieved and the rectifying characteristic was observed in the molecular device. Based on the measurement of transient photocurrent of molecular device, the unidirectional flow of electrons was verified.     

Chitosan-iron oxide nano-composite platform for mismatch-discriminating DNA hybridization for Neisseria gonorrhoeae detection causing sexually transmitted disease

Electrochemically fabricated nano-composite film of chitosan (CH)-iron oxide (Fe(3)O(4)) has been used to detect gonorrhoea, a sexually transmitted disease (STD) via immobilization of biotinylated probe DNA (BDNA) using avidin-biotin coupling for rapid and specific (mismatch-discriminating) DNA hybridization. The presence of Fe(3)O(4) nanoparticles (～18nm) increases the electro-active surface area of the nano-biocomposite that provides desirable environment for loading of DNA with better conformation leading to increased electron transfer kinetics between the medium and electrode. The differential pulse voltammetric (DPV) studies have been conducted using BDNA/avidin/CH-Fe(3)O(4)/ITO electrode owing to the reduction of the methylene blue (MB) indicator and investigate electron transfer between MB moieties and electrode for one and two-bases mismatch. This STD biosensor is found to have a detection limit (1 × 10(-15)M) and a wide dynamic range (from 1 × 10(-16)M to 1 × 10(-6)M) using the complementary target DNA. In addition, the sensing system can be utilized to accurately discriminate complementary sequence from mismatch sequences.     

Enzymatic glucose biosensor based on CeO2 nanorods synthesized by non-isothermal precipitation

Cerium oxide nanorods (CeO(2) NRs) were synthesized without templates through a low cost and simple non-isothermal precipitation method. The structure and morphology of CeO(2) NRs were characterized by X-ray diffraction and transmission electron microscopy. The CeO(2) NRs films, deposited on indium tin oxide (ITO)-coated glass substrates through electrophoretic deposition, were used for the immobilization of glucose oxidase (GOx). Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterize the CeO(2) NRs/ITO and GOx/CeO(2) NRs/ITO electrodes. The GOx/CeO(2) NRs/ITO electrode exhibits a linear range for the detection of glucose from 2 to 26 mM (correlation coefficient: 0.99) at 1-2s response time. Biosensor sensitivity is 0.165 μA mM(-1) cm(-2) with 100 μM detection limit. The anti-interference ability of the biosensor was also examined. The mediator-less application of CeO(2) NRs for glucose sensing was demonstrated.     

Photoelectrochemical, photophysical and morphological studies of electrostatic layer-by-layer thin films based on poly(p-phenylenevinylene) and single-walled carbon nanotubes

The preparation of multilayer films based on poly(p-phenylenevinylene) (PPV) and carboxylic-functionalized single-walled carbon nanotubes (SWNT-COOH) by electrostatic interaction using the layer-by-layer (LbL) deposition method is reported herein. The multilayer build-up, monitored by UV-Vis and photoluminescence (PL) spectroscopies, displayed a linear behavior with the number of PPV and SWNT-COOH layers deposited that undergo deviation and spectral changes for thicker films. Film morphology was evaluated by AFM and epifluorescence microscopies showing remarkable changes after incorporation of SWNT-COOH layers. Films without SWNT show roughness and present dispersed grains; films with SWNT-COOH layers are flatter and some carbon nanotube bundles can be visualized. The photoinduced charge transfer from the conducting polymer to SWNT-COOH was analyzed by PL quenching either by the decrease of the emission intensity or by the presence of dark domains in the epifluorescence micrographs. Photoelectrochemical characterization was performed under white light and the films containing SWNT-COOH displayed photocurrent values between 2.0 μA cm(-2) and 7.5 μA cm(-2), as the amount of these materials increases in the film. No photocurrent was observed for the film without carbon nanotubes. Photocurrent generation was enhanced and became more stable when an intermediate layer of PEDOT:PSS was interposed between the active layer and the ITO electrode, indicating an improvement in hole transfer to the contacts. Our results indicate that these multilayer films are promising candidates as active layers for organic photovoltaic cells.     

Lipid membrane immobilized horseradish peroxidase biosensor for amperometric determination of hydrogen peroxide

Stable films of didodecyldimethylammonium bromide (DDAB, a synthetic lipid) and horseradish peroxidase (HRP) were made by casting the mixture of the aqueous vesicle of DDAB and HRP onto the glassy carbon (GC) electrode. The direct electron transfer between electrode and HRP immobilized in lipid film has been demonstrated. The lipid films were used to supply a biological environment resembling biomembrane on the surface of the electrode. A pair of redox peaks attributed to the direct redox reaction of HRP were observed in the phosphate buffer solution (pH 5.5). The cathodic peak current increased dramatically while anodic peak decreased by addition of small amount H(2)O(2). The pH effect on amperometric response to H(2)O(2) was studied. The biosensor also exhibited fast response (5 s), good stability and reproducibility.     

Retarded Charge–Carrier Recombination in Photoelectrochemical Cells from Plasmon‐Induced Resonance Energy Transfer

N‐type metal oxides such as hematite (α‐Fe₂O₃) and bismuth vanadate (BiVO₄) are promising candidate materials for efficient photoelectrochemical water splitting; however, their short minority carrier diffusion length and restricted carrier lifetime result in undesired rapid charge recombination. Herein, a 2D arranged globular Au nanosphere (NS) monolayer array with a highly ordered hexagonal hole pattern (hereafter, Au array) is introduced onto the surface of photoanodes comprised of metal oxide films via a facile drying and transfer‐printing process. Through plasmon‐induced resonance energy transfer, the Au array provides a strong electromagnetic field in the near‐surface area of the metal oxide film. The near‐field coupling interaction and amplification of the electromagnetic field suppress the charge recombination with long‐lived photogenerated holes and simultaneously enhance the light harvesting and charge transfer efficiencies. Consequently, an over 3.3‐fold higher photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) is achieved for the Au array/α‐Fe₂O₃. Furthermore, the high versatility of this transfer printing of Au arrays is demonstrated by introducing it on the molybdenum‐doped BiVO₄ film, resulting in 1.5‐fold higher photocurrent density at 1.23 V versus RHE. The tailored metal film design can provide a potential strategy for the versatile application in various light‐mediated energy conversion and optoelectronic devices.     

Direct electrochemistry and electrocatalytic activity of catalase immobilized onto electrodeposited nano-scale islands of nickel oxide

Cyclic voltammetry was used for simultaneous formation and immobilization of nickel oxide nano-scale islands and catalase on glassy carbon electrode. Electrodeposited nickel oxide may be a promising material for enzyme immobilization owing to its high biocompatibility and large surface. The catalase films assembled on nickel oxide exhibited a pair of well defined, stable and nearly reversible CV peaks at about -0.05 V vs. SCE at pH 7, characteristic of the heme Fe (III)/Fe (II) redox couple. The formal potential of catalase in nickel oxide film were linearly varied in the range 1-12 with slope of 58.426 mV/pH, indicating that the electron transfer is accompanied by single proton transportation. The electron transfer between catalase and electrode surface, (k(s)) of 3.7(+/-0.1) s(-1) was greatly facilitated in the microenvironment of nickel oxide film. The electrocatalytic reduction of hydrogen peroxide at glassy carbon electrode modified with nickel oxide nano-scale islands and catalase enzyme has been studied. The embedded catalase in NiO nanoparticles showed excellent electrocatalytic activity toward hydrogen peroxide reduction. Also the modified rotating disk electrode shows good analytical performance for amperometric determination of hydrogen peroxide. The resultant catalase/nickel oxide modified glassy carbon electrodes exhibited fast amperometric response (within 2 s) to hydrogen peroxide reduction (with a linear range from 1 microM to 1 mM), excellent stability, long term life and good reproducibility. The apparent Michaelis-Menten constant is calculated to be 0.96(+/-0.05)mM, which shows a large catalytic activity of catalase in the nickel oxide film toward hydrogen peroxide. The excellent electrochemical reversibility of redox couple, high stability, technical simplicity, lake of need for mediators and short preparations times are advantages of this electrode. Finally the activity of biosensor for nitrite reduction was also investigated.     

Amperometric detection of morphine at a Prussian blue-modified indium tin oxide electrode

In this work, the electrocatalytic oxidation of morphine (MO) at an optically transparent indium tin oxide (ITO) electrode modified by an electrodeposited Prussian blue (PB) thin film is first demonstrated, and the amperometric detection of MO was then investigated. Experimental results showed that the thin film on the ITO surface, confined to the PB/Berlin green (BG) redox pair, can serve as an excellent mediator which facilitates electron transfer and considerably lowers the overpotential required, as compared to a bare ITO electrode. Thus, PB can be regarded as a promising artificial peroxidase for MO. The rate of such an electrocatalytic reaction is pH dependent with the highest value at pH 5. By potential-step excitation from 0.55 to 0.70 V, a linear calibration curve, displaying the relationship between steady-state currents and MO concentrations (ranging from 0.09 to 1.0 mM), was obtained. The detection sensitivity is about 16.8 microA/cm2 mM. Most importantly, the method described herein can readily discriminate MO analogs lacking the phenolic -OH group, such as codeine, and can thus benefit the specific recognition of MO.     

Disposable superoxide anion biosensor based on superoxide dismutase entrapped in silica sol–gel matrix at gold nanoparticles modified ITO electrode

A novel disposable biosensor based on direct electron transfer of superoxide dismutase (SOD) was fabricated for the determination of superoxide anion. The biosensor was constructed by electrodeposition of gold nanoparticles (GNPs) on the indium tin oxide (ITO) electrode and then immobilization of SOD in silica sol–gel (SG) network in the presence of cysteine on GNPs/ITO modified electrode surface. The distribution of GNPs on ITO electrode surface was examined by scanning electron microscopy (SEM). The immobilized SOD exhibited high catalytical activity towards superoxide anion. Parameters affecting the performance of the biosensor were also investigated. A linear calibration curve was obtained over the range from 0.08 to 0.64 μM with a correlation coefficient of 0.9937. The resulted biosensors were demonstrated to possess striking analytical properties for superoxide anion determination, such as high sensitivity, good accuracy, and long-term stability. It provides a promising platform for the fabrication of disposable biosensors.