Sol-gel-derived titanium oxide/copolymer composite based glucose biosensor

A new type of sol-gel-derived titanium oxide/copolymer composite material was developed and used for the construction of glucose biosensor. The composite material merged the best properties of the inorganic species, titanium oxide and the organic copolymer, poly(vinyl alcohol) grafting 4-vinylpyridine (PVA-g-PVP). The glucose oxidase entrapped in the composite matrix retained its bioactivity. Morphologies of the composite-modified electrode and the enzyme electrode were characterized with a scanning electron microscope. The dependence of the current responses on enzyme-loading and pH was studied. The response time of the biosensor was < 20 s and the linear range was up to 9 mM with a sensitivity of 405 nA/mM. The biosensor was stable for at least I month. In addition, the tetrathiafulvalene-mediated enzyme electrode was constructed for the decrease of detection potential and the effect of three common physiological sources that might interfere was also investigated.

Co-immobilized microbial biosensor for BOD estimation based on sol-gel derived composite material

A novel type of biochemical oxygen demand (BOD) biosensor was developed for water monitor, based on co-immobilizing of Trichosporon cutaneum and Bacillus subtilis in the sol-gel derived composite material which is composed of silica and the grafting copolymer of poly (vinyl alcohol) and 4-vinylpyridine (PVA-g-P(4-VP)). Factors that influence the performance of the resulting biosensor were examined. The biodegradable substrate spectrum could be expanded by the co-immobilized microorganisms. The biosensor prepared also exhibited good reproducibility and long-term stability. Good agreement was obtained between the results of the sensor BOD measurement and those obtained from conventional BOD5 method for water samples.

Electrochemical recognition of alkali metal ions at the micro-water 1,2-dichloroethane interface using a calix[4]arene derivative

In this paper, a calix[4]arene derivative, 5,11,17,23-butyl-25,26,27,28-tetra-(ethanoxycarbonyl)-methoxy-calix[4]arene (L), is investigated as a host to recognize alkali metal ions (Li+, Na+, K+, Rb+ and Cs+) at the interface between two immiscible electrolyte solutions (ITIES). Well-defined cyclic voltammograms are obtained at the micro- and nano-water \ 1,2-dichloroethane (W \ DCE) interfaces supported at micro- and nano-pipets.

Organically modified sol-gel/chitosan composite based glucose biosensor

A new type of organically modified sol-gel/chitosan composite material was developed and used for the construction of glucose biosensor. This material provided good biocompatibility and the stabilizing microenvironment around the enzyme. Ferrocene was immobilized on the surface of glassy carbon electrode as a mediator. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The effects of enzyme-loading, buffer pH, applied potential and several interferences on the response of the enzyme electrode were investigated. The simple and low-cost glucose biosensor exhibited high sensitivity and good stability.

Electrochemical study of PW12O403- in poly(ethylene glycol) electrolyte

The electrochemical properties Of PW12O403- (abbreviated as PW12) anion in poly(ethylene glycol) (PEG) have been studied by cyclic voltammetry, complex impedance and FT-IR spectroscopy. The PW12 anion in PEG-LiClO4 electrolyte shows reasonable facile electrochemistry, and the diffusion coefficients Of PW12 were measured with microelectrode. It is shown that ionic conductivity of polymer electrolytes based on low molecular weight PEG can be improved by the addition of PW12. The increase of conductivity is coupled with decrease of transient cross-links density of polymer chains which is evidenced by the downshift of C-O-C stretching mode. The phenomena are explained in view of ion-ion and ion-polymer interactions.

Electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40), in polyethylene glycol

The electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40) (abbreviated as PMo12-Co), have been studied in poly(ethylene glycol) for four different molecular weights (PEG, average MW 400, 600, 1000, and 2000 g mol(-1)) and containing LiClO4 (O/Li=100/1) supporting electrolyte. The diffusion coefficients of the PMo12-Co nanoparticles were determined using a microelectrode by chronoamperometry for PEG of different molecular weights that were used to describe the diffusion behavior of PMo12-Co nanoparticles in different phase states. Moreover, the conductivity of the composite system increases upon addition of PMo12-Co nanoparticles, which was measured by an a.c. impedance technique. FT-IR spectra and DSC were used to follow the interactions of PEG-LiClO4-PMo12-Co, and well described the reason that the PMo12-Co nanoparticles could promote the conductivity of the PEG-LiClO4-PMo12-Co system.

Fabrication of integrated microelectrodes for electrochemical detection on electrophoresis microchip by electroless deposition and micromolding in capillary technique

A new method for the fabrication of an integrated microelectrode for electrochemical detection (ECD) on an electrophoresis microchip is described. The pattern of the microelectrode was directly made on the surface of a microscope slide through an electroless deposition procedure. The surface of the slide was first selectively coated with a thin layer of sodium silicate through a micromolding in capillary technique provided by a poly(dimethylsiloxane) (PDMS) microchannel; this left a rough patterned area for the anchoring of catalytic particles. A metal layer was deposited on the pattern guided by these catalytic particles and was used as the working electrode. Factors influencing the fabrication procedure were discussed. The whole chip was built by reversibly sealing the slide to another PDMS layer with electrophoresis microchannels at room temperature. This approach eliminates the need of clean room facilities and expensive apparatus such as for vacuum deposition or sputtering and makes it possible to produce patterned electrodes suitable for ECD on microchip under ordinary chemistry laboratory conditions. Also once the micropattern is ready, it allows the researchers to rebuild the electrode in a short period of time when an electrode failure occurs. Copper and gold microelectrodes were fabricated by this technique. Glucose, dopamine, and catechol as model analytes were tested.

A strategy for constructing a hybrid bilayer membrane based on a carbon substrate

We construct a hybrid bilayer membrane (HBM) on a new substrate-carbon electrode. It is an extension of HBM based on other substrates. Primary alkylamine was chemically modified onto the surface of a carbon electrode by electrochemical scans; thus, a monolayer was formed on the electrode. Because the alkane chains section is toward the outside, a hydrophobic surface was constructed. Then a lipid monolayer was spread on the hydrophobic surface of the carbon electrode. The formed HBM was characterized by electrochemical and ATR-FT-IR methods. From ATR-FT-IR results, the lipid order parameter (S) of 0.73 was obtained. This kind of hybrid membrane has the advantages of a lipid/alkanethiol HBM. A potential application of this HBM as a biosensor (detecting K+) was given.

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 H2O2. The pH effect on amperometric response to H2O2 was studied. The biosensor also exhibited fast response (5 s), good stability and reproducibility.

Hydrogen peroxide biosensor based on microperoxidase-11 entrapped in lipid membrane

A highly catalytic activity microperoxidase-11 (MP-11) biosensor for H2O2 was developed to immobilizing the heme peptide in didodecyldimethylammonium bromide (DDAB) lipid membrane. The enzyme electrode thus obtained responded to H2O2 without electron mediator or promoter, at a potential of +0.10 V versus Ag \ AgCl. A linear calibration curve is obtained over the range from 2.0 x 10(-5) to 2.4 x 10(-3) M. The biosensor responds to hydrogen peroxide in 15 s and has a detection limit of 8 x 10(-7) M (S/N = 3) Providing a natural environment with lipid membrane for protein immobilization and maintenance of protein functions is a suitable option for the design of biosensors.

Electrochemical and spectroscopic study on the interaction of cytochrome c with anionic lipid vesicles

The structure and the electron-transfer of cytochrome c binding on the anionic lipid vesicles were analyzed by electrochemical and various spectroscopic methods. It was found that upon binding to anionic lipid membrane, the formal potential of. cytochrome c shifted 30 mV negatively indicating an eager redox interaction than that in its native state. This is due to the local alteration of the coordination and the heme crevice. The structural Perturbation in which a molten globule-like state is formed during binding to anionic lipid vesicles is more important. This study may help to understand the mechanism of the electron-transfer reactions of cytochrome c at the mitochondrial membrane.

Layer-by-layer assembly of multilayer films composed of avidin and biotin-labeled antibody for immunosensing

Protein multilayers composed of avidin and biotin-labeled antibody (bio-Ab) were prepared on gold surface by layer-by-layer assembly technology using the high specific binding constant (K-a: approximate to 10(15) M-1) between avidin and biotin. The assembly process of the multilayer films was monitored by using real-time BIA technique based on surface plasmon resonance (SPR). The multilayer films were also characterized by electrochemical impedance spectroscopy (EIS) and reflection absorption Fourier transform infrared spectroscopy (FTIR). The results indicate that the growth of the multilayer is uniform. From response of SPR for each layer, the stoichiometry S for the interaction between avidin and bio-Ab is calculated to be 0.37 in the multilayer whereas 0.82 in the first layer. The protein mass concentration for each layer was also obtained. The schematic figure for the multilayer assembly was proposed according to the layer mass, concentration and S value. The utility of the mutilayer films for immunosensing has been investigated via their subsequent interaction with hIgG. The binding ability of the multilayer increased for one to three layers of antibody, and then reach saturation after the fourth layer. These layer-by-layer constructed antibody multilayers enhance the binding ability than covalently immobilized monolayer antibody. This technology can be also used for construction of other thin films for immunosensing and biosensor.

Real-time immunoassay of ferritin using surface plasmon resonance biosensor

A surface plasmon resonance (SPR) biosensor was used for the first time to determine the concentration of ferritin in both HBS-EP buffer and serum. The monoclonal antibody was immobilized on the carboxymethyl dextran-modified gold surface by an amine coupling method. The interaction of antibody with antigen was monitored in real-time. The signal was enhanced by sandwich amplification strategy to improve the sensitivity and specificity of the immunoassay, especially in serum. The linear range of the assay in serum is over 30-200 ng ml with the detection limit of 28 ng ml(-1). The sensitivity, specificity, and reproducibility of the assay are satisfactory. The analyte and enhancement antibody-binding surface could be regenerated by pH 2.0 glycine-HCl buffer and the same antibody-immobilized surface could be used for more than 50 cycles of ferritin binding and regeneration.

Amplified DNA detection sensitivity using streptavidin-biotinylated protein complex: Characterization by electrochemical impedance spectroscopy

Thiol-terminated oligonucleotide was immobilized to gold surface by self-assembly method. A novel amplification strategy was introduced for improving the sensitivity of DNA. hybridization using biotin labeled protein-streptavidin network complex. This complex can be formed in a cross-linking network of molecules so that the amplification of the response signal will be realized due to the big molecular size of the complex. It could be proved from the impedance technique that this amplification strategy caused dramatic improvement of the detection sensitivity. These results give significant advances in the generality and sensitivity as it is applied to biosensing.