A graphene-laminated electrode with high glucose oxidase loading for highly-sensitive glucose detection

Graphene oxide(GO) has received considerable attention for glucose detection because of high surface area, abundant functional groups, and good biocompatibility. Defects and functional groups of the GO are beneficial to immobilization of glucose oxidase(GOD), but sacrificing electron-transfer capability for highly-sensitive detection. In order to obtain high GOD loading and highly-sensitive detection of biosensors, we first designed and fabricated a graphene-laminated electrode by combining GO and edgefunctionalized graphene(FG) layers together onto glassy-carbon electrode. The graphene-laminated electrodes exhibited faster electron transfer rate, higher GOD loading of 3.80 × 10^-9 mol·cm^-2, and higher detection sensitivity of 46.71 μA·mM^-1·cm^-2 than other graphene-based biosensors reported in literature. Such high performance is mainly attributed to the abundant functional groups of GO, high electrical conductivity of FG, and strong interactions between components in the graphene-laminated electrodes.By virtue of their high enzyme loading and highly-sensitive detection, the graphene-laminated electrodes show great potential to be widely used as high-performance biosensors in the field of medical diagnosis.     

Glucose fast-response amperometric sensor based on glucose oxidase immobilized in an electropolymerized poly(o-phenylenediamine) film

o-Phenylenediamine has been used for glucose oxidase (GOx) immobilization on Pt electrodes by electrochemical polymerization at +0.65 V vs SCE. By this approach the enzyme is entrapped in a strongly adherent, highly reproducible thin membrane, whose thickness is around 10 nm. This one-step procedure produces a glucose sensor with a response time less than 1 s, an active enzyme loading higher than 3 units/cm2 of electrode surface, a high sensitivity, and a sufficiently wide linear range. The glucose response shows an apparent Michaelis-Menten constant, K'm = 14.2 mM, and a limiting current density, jmax of 181 microA/cm2. The product kD of partition and diffusion coefficients of glucose in the polymer film is on the order of 10(-13) cm2/s. Due to permselectivity characteristics of the membrane, the access of ascorbate, a common interfering species, to the electrode surface is blocked. To our knowledge, this represents the first report of a membrane capable, at the same time, of immobilizing GOx and rejecting ascorbate. The interesting electrode behavior can be rationalized by using an existing model predicting the amperometric response of an immobilized GOx system.     

壳聚糖凝胶材料固定葡萄糖氧化酶制电极的研究

以壳聚糖为载体研究凝胶法固定葡萄糖氧化酶制电极。试验研究了载体壳聚糖的降解性；交联剂戊二醛的浓度、用量；电极的载酶量等固定化条件对所组建的传感器性能的影响。通过影响规律的分析、优化固定化条件的研究，找出了根据壳聚糖溶液粘度适当调整交联剂成二醛的用量和铂丝在酶膜母液中浸涂时间，克服壳聚糖的降解性对酶电极性能的影响，建立了制备性能相近的GOD传感器的方法。     

Selective determination of sucrose based on electropolymerized molecularly imprinted polymer modified multiwall carbon nanotubes/glassy carbon electrode

A novel and selective electrochemical sensor was successfully developed for the determination of sucrose by integrating electropolymerization of molecularly imprinted polymer with multiwall carbon nanotubes. The sensor was prepared by electropolymerizing of o-phenylenediamine in the presence of template, sucrose, on a multiwall carbon nanotube-modified glassy carbon electrode. The sensor preparation conditions including sucrose concentration, the number of CV cycles in the electropolymerization step, pH of incubation solution, extraction time of template from the imprinted film and the incubation time were optimized using response surface methodology (RSM). A mixture of acetonitrile/acetic acid was used to remove the template. Hexacyanoferrate(II) was used as a probe to characterize the sensor using electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. Capturing of sucrose by the modified electrode causes decreasing the response of the electrode to hexacyanoferrate(II). Calibration curve was obtained in the sucrose concentration range of 0.01–10.0 mmol L^? 1 with a limit of detection 3 μmol L^? 1. This sensor provides an efficient way for eliminating interferences from compounds with similar structures to sucrose. The sensor was successfully used to determine sucrose in sugar beet juices with satisfactory results.     

Organic conducting polymer electrode based sensors for detection of Salmonella infecting bacteriophages

There is interest in using bacteriophage as an indicator for the presence of pathogens, such as Salmonella, in health care and food processing environments. However, the current plaque assay technique to detect bacteriophages is time consuming and laboratory based. The following reports on a bacteriophage sensor based on conducting polymer organic electrodes modified with phage host cells (Salmonella Newport). Conducting polymer electrodes were fabricated by chemical deposition of polypyrrole onto the surface of a microporous polycarbonate membrane. The formed films exhibited quasi-reversible redox behaviour which was dominated by anion exchange although cations also contributed to the charge transfer kinetics. Salmonella host cells were absorbed onto the surface of the film and reacted with infecting bacteriophage in LBM broth at 37 °C. Upon bacteriophage mediated host cell lysis the impedance of the supporting polypyrrole electrode increased especially in relation to Z″. It is proposed that the increase in the dielectric properties of the polypyrrole layer was caused by the interaction of cellular constituents derived from the lysed cells. From dose response curves it was found that the sensor could detect 3 log Plaque Forming Units (pfu)/ml within 270 min although no linear correlation between phage concentration and sensor response was observed.     

A novel Ni-CERMET electrode based on a proton conducting electrolyte

Based on the one-chamber fuel cell design by Iwahara a catalytic methane sensor has been developed. The working principle of this sensor is based on the difference in catalytic properties of two electrodes for the CO₂ reforming reaction of methane. The sensor is based on a high-temperature proton conducting electrolyte, i.e. SrCe_0.95Yb_0.05O_3– or CaZr_0.9In_0.1O_3–. At 500 °C a linear sensor response on the methane partial pressure has been found for a Ru/SrCe_0.95Yb_0.05O_3–/Pt cell. This cell, however, shows poor long-term stability. The long-term stability of the Ru/SrCe_0.95Yb_0.05O_3–/Pt cell is improved using a more stable electrolyte material, i.e. CaZr_0.9In_0.1O_3–(CZI10). Further improvement of the long-term stability of the sensor is achieved using a nickel-CaZr_0.9In_0.1O_3– CERMET (Ni-CZI10) electrode. The sensor response of a Ni-CZI10/CaZr_0.9In_0.1O_3–/Pt cell is found to be linear at 600 °C and 700 °C, respectively. The temperature dependence of both the Ru/SrCe_0.95Yb_0.05O_3–/Pt and the Ni-CZI10/CaZr_0.9In_0.1O_3–/Pt cell can be explained by the temperature dependence of the catalytic activity of the electrode materials used. This confirms that the obtained EMF is established by a catalytic activity difference between both electrodes. The power output of a Ni-CZI10/CaZr_0.9In_0.1O_3–/Pt cell is also determined. A combined sensor-fuel cell would have the advantage that it is able to detect the fuel concentration in the gas and, therefore, correct in-situ for fluctuations in the fuel concentration. The power output of the Ni-CZI10/CaZr_0.9In_0.1O_3–/Pt cell, however, is found to be 0.01 mW · cm^–2. This low power output, with respect to values reported in literature for the one-chamber fuel cell, can be explained by the relatively thick electrolyte used, the electrode materials chosen, and the use of the reforming reaction of methane instead of the partial oxidation of methane. However, the feasibility of the combined sensor-fuel cell has been demonstrated.     

Fundamental studies of glucose oxidase deposition on a Pt electrode.

The direct electrodeposition of glucose oxidase (EC 1.1.3.4) on a platinum electrode was investigated as a means for controlled immobilization. The presence of a nonionic detergent, Triton X-100, was found essential to produce a multilayered deposit. Moreover, to work properly, the detergent must be present above its critical micelle concentration. Under these conditions, a deposit of approximately 50 enzyme layers (480 nm), with surface uniformity of +/-20 nm, was verified using an electrochemical quartz crystal microbalance and by atomic force microscopy. In the absence of detergent, a layer of 25 nm is formed. Contrary to most previous claims, the deposition, which is potential dependent but optimal at 1.3 V versus AgCl/Ag electrode, is not electrophoretically driven, but is instead controlled by a lowering of the pH at the electrode surface due to concomitant oxygen evolution.     

Voltammetric heparin-selective electrode based on thin liquid membrane with conducting polymer-modified solid support

A novel, solid-supported voltammetric ion-selective electrode to detect anticoagulant/antithrombotic heparin at polarizable poly(vinyl chloride) (PVC) membrane/water interfaces was developed. An approximately 3-4.5-microm-thick PVC membrane plasticized with 2-nitrophenyl octyl ether was supported on a gold electrode modified with a poly(3-octylthiophene) (POT) film as an ion-to-electron transducer. Charge transport through the PVC-covered POT film is electrochemically reversible, as demonstrated by cyclic voltammetry with nonpolarizable membrane/water interfaces. In addition to the fast charge transport, adequate redox capacity of the POT film and a small ohmic potential drop in the thin PVC membrane enable ion transfer voltammetry at polarizable macroscopic membrane/water interfaces in a standard three-electrode cell. Reversible ClO4- transfer at the interfaces coupled with oxidation of a neutral POT film was examined by cyclic voltammetry to determine the distribution of the applied potential to the two polarizable interfaces by convolution technique. Interfacial adsorption and desorption of heparin facilitated by octadecyltrimethylammonium were studied also by cyclic voltammetry and convolution technique to demonstrate that the processes are electrochemically irreversible. Stripping voltammetry based on the interfacial processes gives a low detection limit of 0.005 unit/mL heparin in a saline solution, which is slightly lower than the detection limit of most sensitive heparin sensors reported so far (0.01 unit/mL).     

A pH-sensitive theranostics system based on doxorubicin conjugated with the comb-shaped polymer coating of quantum dots

A two-phase route was developed to form a new theranostics-based system. The comb polymer poly (glycidyl methacrylate)-graft-ethane diamine-graft-polyethylene glycol (PGMA-g-EDA-g-PEG) was used to modify the quantum dots (QDs) by the method of ligand exchange. Subsequently, due to a large amount of amino groups on the surface of QDs, the doxorubicin (DOX) was conjugated by amine bonds to form pH-sensitive drug release system. UV–vis transmission spectra and PL spectra showed that the nanoparticles maintained the optical properties of QDs and DOX. The transmission electron microscopy analysis indicated that QDs were well dispersed in water and still had small sizes (7 nm) after ligand exchange and conjugated with DOX. Then the thermogravimetric analysis (TGA) revealed that about 80 wt% comb-shaped polymers coated on the surface of QDs, and about 10 wt% QDs was in nanoparticles PGMA-g-EDA-g-PEG-QDs-DOX. In vitro release studies showed that PGMA-g-EDA-g-PEG -DOX and PGMA-g-EDA-g-PEG-QDs-DOX were pH sensitive. Findings from this study suggested that nanoparticles PGMA-g-EDA-g-PEG-QDs-DOX can be used in a new field combined both imaging and targeted therapy.     

聚合物基透明导电材料研究进展

综述了网络掺杂聚合物、本征导电高聚物、超微导电颗粒／超细导电纤维真充聚合物等3种聚合物基透明导电材料的制备方法、研究历史和发展现状。     

合成电势对Li／聚吡咯正极性能的影响

为了简便真实的分析聚合电势对叫聚吡咯电池正极电化学行为的影响，同时寻找最佳聚合电势，在pt微盘电极上用恒电位法合成聚吡咯（PPy），通过循环伏安，计时电势方法对电化学行为进行检测，结果表明：当聚合区间为3．8-4．2V（VSLi／Li^＋）时，PPy膜电极均具有较好的可遗陛和电化学容量。选择4．0V（VS Li／Li^＋）电位聚合，PPy微电极的电化学陛能更佳。通过SEM测试技术进一步分析表明，不同电位直接影响聚吡咯的形貌，这是导致电池可逆性不同的直接原因；选择4．0V电势进行聚合，可以得到满足二次电池充放电性能要求的PPy膜电极。     

Lithium ion conducting solid polymer blend electrolyte based on bio-degradable polymers

Lithium ion conducting polymer blend electrolyte films based on poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) with different Mwt% of lithium nitrate (LiNO₃) salt, using a solution cast technique, have been prepared. The polymer blend electrolyte has been characterized by XRD, FTIR, DSC and impedance analyses. The XRD study reveals the amorphous nature of the polymer electrolyte. The FTIR study confirms the complex formation between the polymer and salt. The shifts in T _g values of 70 PVA–30 PVP blend and 70 PVA–30 PVP with different Mwt% of LiNO₃ electrolytes shown by DSC thermograms indicate an interaction between the polymer and the salt. The dependence of T _g and conductivity upon salt concentration has been discussed. The ion conductivity of the prepared polymer electrolyte has been found by a.c. impedance spectroscopic analysis. The PVA–PVP blend system with a composition of 70 wt% PVA: 30 wt% PVP exhibits the highest conductivity of 1·58 × 10^???6 Scm^???1 at room temperature. Polymer samples of 70 wt% PVA–30 wt% PVP blend with different molecular weight percentage of lithium nitrate with DMSO as solvent have been prepared and studied. High conductivity of 6·828 × 10^???4 Scm^???1 has been observed for the composition of 70 PVA:30 PVP:25 Mwt% of LiNO₃ with low activation energy 0·2673 eV. The conductivity is found to increase with increase in temperature. The temperature dependent conductivity of the polymer electrolyte follows the Arrhenius relationship which shows hopping of ions in the polymer matrix. The relaxation parameters (ω) and (τ) of the complexes have been calculated by using loss tangent spectra. The mechanical properties of polymer blend electrolyte such as tensile strength, elongation and degree of swelling have been measured and the results are presented.     

Hybrid amperometric and conductometric chemical sensor based on conducting polymer nanojunctions

We report on a hybrid chemical sensor that can perform either amperometric or conductometric detection alone or simultaneously. It consists of an array of electrode pairs in which the two electrodes in each pair are separated with micrometer to nanometer-scale gaps. The gaps are bridged with conducting polymer (polyaniline) so that one can measure the conductance of the polymer bridge like a conventional Chem-FET. The electrode geometries are designed to allow simultaneously detection of electrochemical current like a conventional microelectrode amperometric sensor. The hybrid device provides increased selectivity for detection of analytes in complex matrixes and may provide new insights into the electrochemical reaction mechanisms of analytes. As an example, we have demonstrated the detection of dilute neurotransmitter (dopamine) in the presence of its concentrated major physiological interferent, ascorbic acid, which is not possible using either the amperometric or the conductometric techniques alone.     

A wireless, remote query glucose biosensor based on a pH-sensitive polymer

This paper describes a wireless, remote query glucose biosensor using a ribbonlike, mass-sensitive magnetoelastic sensor as the transducer. The glucose biosensor is fabricated by first coating the magnetoelastic sensor with a pH-sensitive polymer and upon it a layer of glucose oxidase (GOx). The pH-responsive polymer swells or shrinks, thereby changing mass, respectively, in response to increasing or decreasing pH values. The GOx-catalyzed oxidation of glucose produces gluconic acid, inducing the pH-responsive polymer to shrink, which in turn decreases the polymer mass. In response to a time-varying magnetic field, a magnetoelastic sensor mechanically vibrates at a characteristic resonance frequency, the value of which inversely depends on sensor mass loading. As the magnetoelastic films are magnetostrictive, the vibrations launch magnetic flux that can be remotely detected using a pickup coil. Hence, changes in the resonance frequency of a passive magnetoelastic transducer are detected on a remote query basis, without the use of physical connections to the sensors.The sensitivity of the glucose biosensors decreases with increasing ionic strength; at physiological salt concentrations, 0.6 mmol/L of glucose can be measured. At glucose concentrations of 1-10 mmol/L, the biosensor response is reversible and linear, with the detection limit of 0.6 mmol/L corresponding to an error in resonance frequency determination of 20 Hz. Since no physical connections between the sensor and the monitoring instrument are required, this sensor can potentially be applied to in vivo and in situ measurement of glucose concentrations.     

Multilayer membranes via layer-by-layer deposition of glucose oxidase and Au nanoparticles on a Pt electrode for glucose sensing

We prepared multilayer membranes by the layer-by-layer deposition of glucose oxidase (GOx) and Au nanoparticles (5, 10, or 50 nm φ) on sensor substrates, such as a Pt electrode and a quartz glass plate, to prepare glucose sensors. The enzyme activity of GOx remained even in alternate assemblies, and the activity increased with the increasing number of depositions. The apparent K_m values of the deposited GOx were 28–32 mM, while a reported value in a solution is 33 mM. These results suggest that Au nanoparticles can be used as binders for the deposition of GOx without significant change in the affinity between GOx and glucose.     

Enzyme-based bilayer conducting polymer electrodes consisting of polymetallophthalocyanines and polypyrrole-glucose oxidase thin films.

Bilayer conducting polymer electrodes, which consist of a polymetallophthalocyanine (PMePc) and polypyrrole incorporating glucose oxidase (PPy-GOx), were prepared on the glassy-carbon electrode by the successive electrochemical deposition of two different polymers. The bilayer film electrodes showed catalytic behavior, which included an enhanced amperometric response current with the substrate and a significantly shifted oxidation potential (approximately 700 mV) of the response current. The bilayer electrodes also showed a fast response time and good stability with the substrate. A bilayer microelectrode, which was prepared by using both PCuPc and PPy-GOx polymer films, also showed a good amperometric response with the substrate.     

Synthesis and characterization of activated carbon/conducting polymer composite electrode for supercapacitor applications

Activated carbon is prepared from coconut shell by heating it around 500?°C for 2 h in a muffle furnace. This method is one of the easiest and most economical methods for the synthesis of Activated carbon. The dried coconut shell is carbonized and it is treated with KOH in the ratio of 1:3 carbon-activating agent (KOH) and the resulting slurry is dried in an oven at 60?°C for overnight. The dried mass is further activated at 450?°C then it is washed with an acid solution to remove KOH. The surface area of the synthesized activated carbon can be obtained by using nitrogen absorption–desorption experiment. Conducting polymer such as polyaniline prepared by oxidative polymerization of the respective monomer in tetrafluoroboric acid solution using potassium persulphate as an oxidant. The structure and doping of polyaniline were studied by FTIR, UV and Cyclic voltammetry studies. The conducting polymer is mixed with AC and prepared composites were characterized by UV, FTIR, and CV. The specific capacitance of composites calculated from charge–discharge at 0.5 mA g^??1 was found to be 99.6 Fg^??1 and for cyclic voltammetry, at the scan rate of 2 mV s^??1, it is 77 Fg^??1.     

Amperometric glucose biosensor based on in situ electropolymerized polyaniline/poly(acrylonitrile-co-acrylic acid) composite film

A new type of in situ electropolymerization was used for electrochemical biosensor design. The biologic film was prepared by in situ electropolymerization of aniline into microporous poly(acrylonitrile-co-acrylic acid)-coated platinum electrode in the presence of glucose oxidase. The results of EIS and SEM indicated the successful immobilization for enzyme in the composite polymer film. The novel glucose biosensor exhibited good selectivity and operational stability, which showed no apparent loss of activity after 40 consecutive measurements and intermittent usage for 45 days with storage in a phosphate buffer solution at 4°C. In addition, optimization of the biosensor construction as well as effects of applied potential, pH value of solution, temperature and common interfering compounds on the amperometric response of the sensor were investigated and discussed.