Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Nickel hexacyanoferrate (NiHCF) nanotubes are fabricated by an electrokinetic method based on the distinct surface properties of porous anodic alumina. By this method, nanotubes can be formed rapidly with the morphologies faithfully replicating the nanopores in the template. The prepared nanotubes were carefully characterized using SEM and TEM. Results from IR, UV, EDX, and electrochemical measurements show that the NiHCF nanotubes exist only in the form of K₂Ni[Fe(CN)₆]. Because of this single composition and unique nanostructure, NiHCF nanotubes show excellently stable cesium-selective ion-exchange ability. The capacity for electrodes modified with NiHCF nanotubes after 500 potential cycles retains 95.3 % of its initial value. Even after 1500 and 3000 cycles, the NiHCF nanotubes still retain 92.2 % and 82.9 %, respectively, of their ion-exchange capacity.

We report on the synthesis of three-dimensionally ordered structure (3D) of macroporous cytochrome c (cyt-c) biofilms by using the inverted colloidal polystyrene crystal template technique and Triton X-100 as entrapping matrix. Electrochemical impedance spectroscopic (EIS) measurements reveal that the immobilized cyt-c molecules exhibit fast interfacial electron-communication rate. We found that the orientation of the cyt-c molecules entrapped in the 3D macroporous structure was determined by the interfacial electric field. Higher interfacial electric field limits the reorientational flexibility of the entrapped cyt-c molecules, resulting in lower intermolecular electron-communication rate constant (k°). Therefore, the highest intermolecular electron-communication rate constant can only be obtained at potentials approaching to the potential of zero charge of the gold electrode, since k° is mainly determined by the molecular orientation in the biofilm. In addition, the prepared biofilms with enhanced functional density could find potential application in the bioelectronic sensing system.

Because of its high activity and selectivity toward the reduction of hydrogen peroxide and oxygen, Prussian blue (PB) is usually considered as an “artificial enzyme peroxidase” and has been extensively used in the construction of electrochemical biosensors. In this study, we report on the construction of amperometric biosensors via grafting PB nanoparticles on the polymeric matrix of multiwalled carbon nanotubes (MWCNTs) and poly(4-vinylpyridine) (PVP). The MWCNT/PVP/PB composite films were synthesized by casting films of MWCNTs wrapped with PVP on gold electrodes followed by electrochemical deposition of PB on the MWCNT/PVP matrix. The electrode modified with the MWCNT/PVP/PB composite film shows prominent electrocatalytic activity toward the reduction of hydrogen peroxide, which can be explained by the remarkable synergistic effect of the MWCNTs and PB. Therefore, fast amperometric response of this sensor to hydrogen peroxide was observed with a detection sensitivity of 1.3 μA μM^–1 of H₂O₂ per square centimeter area and a detection limit of 25 nM. These results are much better than those reported for PB-based amperometric sensors. In addition, a glucose biosensor fabricated by casting an additional glucose oxidase (GOD) containing Nafion film above the MWCNT/PVP/PB composite film shows promise for the sensitive and fast detection of glucose. The observed high stability, high sensitivity, and high reproducibility of the MWCNT/PVP/PB composite films make them promising for the reliable and durable detection of hydrogen peroxide and glucose.

Nanoscale materials directly interfacing semiconductors is a new area of nanoscience and nanotechnology. Tremendous attention has been paid to inorganic nano size crystals in recent years because of their significant properties. Prussian blue (PB) and its analogues could play important roles in the field of molecule-based magnets, electrochromic materials, ion selectivity electrodes and biosensors. In this study, we report on fabricating Prussian blue patterns on silicon surface by combining the photolithographic techniques and galvanic displacement reaction, and the resulting patterns were characterized by scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) on the basis of detection of catalytic current for the oxidation of H₂O₂.

Herein, we have successfully introduced the stimuli-response concept into the controllable synthesis of gold nanoparticles (AuNPs) with designed properties. We used a pH-responsive zwitterionic polymer that acted as a template and a stabilizer. Gold colloids prepared in situ from the polymer solution have a narrow size distribution of about 5 nm. The assembly and disassembly of AuNPs can be finely tuned by modulating the net charges of the zwitterionic polymer so that they are either positive or negative as a function of the solution pH. Different aggregates and colors appear on altering the solution pH. In acidic solutions, gold colloids form large symmetrical aggregates, while the AuNPs disperse in solutions with a pH≈9.6. However, as the solution pH increases (>9.6), needle-like aggregates with a small interparticle distances are formed. On the basis of TEM, SEM, ¹H NMR and UV/Vis measurements, we attribute pH-triggered aggregation and color changes of the gold colloids to the ionization process and conformational change of the polymer. The ionization process governs the choice of ligand anchored on the surface of AuNPs, and the conformational change of the polymer modulates the interspaces between AuNPs. The present approach, which is based on a rational design of the physicochemical properties of the template used in the synthesis process, provides a powerful means to control the properties of the nanomaterial. Furthermore, the colorimetric readout can be visualized and applied to future studies on nanoscale switches and sensors.

Templated nanotubes: Electroosmotic flow causes charged ions to move into nanochannels of a porous membrane when a potential is applied (see picture). A reaction zone is established in the channels, and nanotubes are deposited. Subsequent dissolution of the membrane yields an array of nanotubes.

Direct glucose sensing on highly ordered platinum-nanotubule array electrodes (NTAEs) is systematically investigated. The NTAEs are fabricated by electrochemical deposition of platinum in a 3-aminopropyltrimethoxysilane-modified anodic alumina membrane. Their structures and morphologies are then characterized using X-ray diffraction and scanning electron microscopy, respectively. Electrochemical results show that NTAEs with different real surface areas could be achieved by controlling the deposition time or by using anodic alumina membranes with different pore size. Electrochemical responses of the as-synthesized NTAEs to glucose in a solutions of either 0.5 M H₂SO₄, or phosphate-buffered saline (PBS, pH 7.4) containing 0.1 M KCl are discussed. Based on the different electrochemical reaction mechanisms of glucose and interferents such as p-acetamedophenol and ascorbic acid, their high roughness factor makes NTAEs sensitive, selective, and stable enough to be a kind of biosensor for the non-enzymatic detection of glucose. Such a glucose sensor allows the determination of glucose in the linear range 2–14 mM, with a sensitivity of 0.1 μA cm^–2 mM^–1 (correlation coefficient 0.999), and a detection limit of 1.0 μM glucose, with neglectable interference from physiological levels of 0.1 mM p-acetamedophenol, 0.1 mM ascorbic acid, and 0.02 mM uric acid.

Application of protein-based, direct electron communication in bioelectronic devices, biosensors, or biofuel cells usually requires high stability and function density of the immobilized proteins or enzymes. Traditional methods have been used to increase the function density using multilayer immobilization techniques at the expense of losing stability and electron-communication rate, that is, generally only protein molecules near the electrode surface are electroactive. In order to overcome the above problems, a three-dimensional, ordered, macroporous gold film electrode is synthesized electrochemically by an inverted colloidal crystal template technique. The uniform, three-dimensional macroporous gold provides superior conductivity, high stability, and large surface area. Its interconnected macroporous structure, containing gold nanoparticles, significantly enhances the amount of adsorbed hemoglobin (Hb) molecules at the monolayer level and also provides a good microenvironment for retaining the biological activity of the adsorbed protein, as confirmed by electrochemical and attenuated total reflection Fourier-transform infrared spectroscopy. Therefore, direct electron transfer between the adsorbed Hb and the electrode is achieved. Adsorption of Hb on the macroporous gold film electrode is monitored using electrochemical impedance spectroscopy. The saturated adsorption amount, Γ, of the Hb is determined to be 6.55×10^–10 mol cm^–2 with a surface coverage of 88.1 %. The electrochemical behavior and the adsorption mechanism of Hb on the macroporous gold film electrode are discussed on the basis of the experimental results.

A three-dimensionally ordered, macroporous, inverse-opal platinum film was synthesized electrochemically by the inverted colloidal-crystal template technique. The inverse-opal film that contains platinum nanoparticles showed improved electrocatalytic activity toward glucose oxidation with respect to the directly deposited platinum; this improvement is due to the interconnected porous structure and the greatly enhanced effective surface area. In addition, the inverse-opal Pt-film electrode responds more sensitively to glucose than to common interfering species of ascorbic acid, uric acid, and p-acetamidophenol due to their different electrochemical reaction mechanisms. Results showed that the ordered macroporous materials with enhanced selectivity and sensitivity are promising for fabrication of nonenzymatic glucose biosensors.

A dual-electrode configuration for the highly selective detection of glucose in the diffusion layer of the substrate electrode is presented. In this approach, a glassy carbon electrode (GCE, substrate) modified with a conductive layer of glucose oxidase/Nafion/graphite (GNG) was used to create an interference-free region in its diffusion layer by electrochemical depletion of interfering electroactive species. A Pt microelectrode (tip, 5 μm in radius) was located in the diffusion layer of the GNG-modified GCE (GNG-G) with the help of scanning electrochemical microscopy. Consequently, the tip of the electrode could sense glucose selectively by detecting the amount of hydrogen peroxide (H₂O₂) formed from the oxidization of glucose on the glucose oxidase layer. The influences of parameters, including tip–substrate distance, substrate potential, and electrolyzing time, on the interference-removing efficiency of this dual-electrode approach have been investigated systematically. When the electrolyzing time was 30 s, the tip–substrate distance was 1.8 a (9.0 μm) (where a is the radius of the tip electrode), the potentials of the tip and substrate electrodes were 0.7 V and 0.4 V, respectively, and a mixture of ascorbic acid (0.3 mM), uric acid (0.3 mM), and 4-acetaminophen (0.3 mM) had no influence on the glucose detection. In addition, the current–time responses of the tip electrode at different tip–substrate distances in a solution containing interfering species were numerically simulated. The results from the simulation are in good agreement with the experimental data. This research provides a concept of detection in the diffusion layer of a substrate electrode, as an interference-free region, for developing novel microelectrochemical devices.