Characterization of novel glucose oxysilane sol–gel electrochemical biosensors with copper hexacyanoferrate mediator

Using MPTMS as permselective membranes of biosensors

A sol-gel material of (3-mercaptopropyl) trimethoxysilane (MPTMS) is proposed to function as permselective membranes of biosensors. Permselectivity of MPTMS and Nafion was compared by studying their anti-interferent ability. Membrane porosity of MPTMS and Nafion was first confirmed via voltammetric responses in ferrocynite/ferricynite solution. In the comparison studies, membranes prepared with 20% MPTMS in phosphate buffer solution (PBS) and 1% Nafion in 2-propanol (IPA) were used as coating materials on the surface of two platinum (Pt) electrodes. These electrodes were used to electrochemically measure the response currents of ascorbic acid, uric acid, and acetaminophen. The results indicate that the MPTMS-based electrode produced much less response currents from the interference species compared to that of the Nafion-based electrode. This denotes that the anti-interferent ability ofMPTMS is superior to that of Nafion. A platinum working electrode containing glucose oxidase (GOx) immobilized by poly-aniline (PA) and then modified by MPTMS was developed and evaluated. The results show that the optimum applied potential for the glucose biosensor is 0.4 V. This operational potential not only inhibits the response currents from ascorbic acid, uric acid, and acetaminophen but also produces rather high signals for glucose.

Organoclay-enzyme film electrodes

This paper aims at showing the interest of organoclays (clay minerals containing organic groups covalently attached to the inorganic particles) as suitable host matrices likely to immobilize enzymes onto electrode surfaces for biosensing applications. The organoclays used in this work were natural Cameroonian smectites grafted with either aminopropyl (AP) or trimethylpropylammonium (TMPA) groups. The first ones were exploited for their ability to anchor biomolecules by covalent bonding while the second category exhibited favorable electrostatic interactions with negatively charged enzymes due to ion exchange properties that were pointed out here by means of multisweep cyclic voltammetry. AP-clay materials were applied to the immobilization of glucose oxidase (GOD) and TMPA-clays for polyphenol oxidase (PPO) anchoring. When deposited onto the surface of platinum or glassy carbon electrodes as enzyme/organoclay films, these systems were evaluated as biosensing electrochemical devices for detection of glucose and catechol chosen as model analytes. The advantageous features of these organoclays were discussed by comparison to the performance of related film electrodes made of non-functionalized clays. It appeared that organoclays provide a favorable environment to enzymes activity, as highlighted from the biosensors characteristics and determination of Michaelis-Menten constants.

Determination of isatin and monoamine neurotransmitters in rat brain with liquid chromatography using palladium hexacyanoferrate modified electrode

The fabrication and application of a novel electrochemical detector (ED) with palladium hexacyanoferrate (PdHCF) chemically modified electrode (CME) for liquid chromatography (LC) were described. The electrochemical behaviors of isatin, monoamine neurotransmitters and their metabolites at this CME were investigated by cyclic voltammetry. It was found that the CME exhibited efficiently electrocatalytic of isatin and showed high sensitivity and stability for determination of monoamine neurotransmitters. The linear ranges were over three orders of magnitude and the detection limits were 2.5 x 10(-8) mol L(-1) for isatin, 2.5 x 10(-10) mol L(-1) for norepinephrine (NE), 2.5 x 10(-10) mol L(-1) for 5-hydroxyindoleacetic acid (5-HIAA), 5.0 x 10(-10) mol L(-1) for dopamine (DA), 1.0 x 10(-9)mol L(-1) for 3,4-dihydroxyphenylacetic acid (DOPAC), 1.2 x 10(-10) mol L(-1) for 5-hydroxytryptamine (5-HT) and 2.5 x 10(-9)mol L(-1) for homovanillic acid (HVA). Combined with microdialysis, the method was successfully applied to study the effect of isatin on the levels of monoamine neurotransmitters in experimental Parkinsonian rats. The results showed that isatin could significantly increase striatal monoamine neurotransmitters release to the basal level.

Enzyme Electrochemistry — Biocatalysis on an Electrode

Oxidoreductase enzymes catalyze single- or multi-electron reduction/oxidation reactions of small molecule inorganic or organic substrates, and they are integral to a wide variety of biological processes including respiration, energy production, biosynthesis, metabolism, and detoxification. All redox enzymes require a natural redox partner such as an electron-transfer protein (e.g. cytochrome, ferredoxin, flavoprotein) or a small molecule cosubstrate (e.g. NAD(P)H, dioxygen) to sustain catalysis, in effect to balance the substrate/product redox half-reaction. In principle, the natural electron-transfer partner may be replaced by an electrochemical working electrode. One of the great strengths of this approach is that the rate of catalysis (equivalent to the observed electrochemical current) may be probed as a function of applied potential through linear sweep and cyclic voltammetry, and insight to the overall catalytic mechanism may be gained by a systematic electrochemical study coupled with theoretical analysis. In this review, the various approaches to enzyme electrochemistry will be discussed, including direct and indirect (mediated) experiments, and a brief coverage of the theory relevant to these techniques will be presented. The importance of immobilizing enzymes on the electrode surface will be presented and the variety of ways that this may be done will be reviewed. The importance of chemical modification of the electrode surface in ensuring an environment conducive to a stable and active enzyme capable of functioning natively will be illustrated. Fundamental research into electrochemically driven enzyme catalysis has led to some remarkable practical applications. The glucose oxidase enzyme electrode is a spectacularly successful application of enzyme electrochemistry. Biosensors based on this technology are used worldwide by sufferers of diabetes to provide rapid and accurate analysis of blood glucose concentrations. Other applications of enzyme electrochemistry are in the sensing of macromolecular complexation events such as antigen–antibody binding and DNA hybridization. The review will include a selection of enzymes that have been successfully investigated by electrochemistry and, where appropriate, discuss their development towards practical biotechnological applications.