Assembling and evaluation of new dehydrogenase enzyme electrode probes obtained by electropolymerization of aminobenzine isomers and PQQ on gold, platinum and carbon electrodes

Electropolymerized poly(Toluidine blue)-modified carbon felt for highly sensitive amperometric determination of NADH in flow injection analysis

Poly(pheniothiazine) films were prepared on a porous carbon felt (CF) electrode surface by an electrooxidative polymerization of three phenothiazine derivatives (i.e.,Tthionine (TN), Toluidine Blue (TB) and Methylene Blue (MB)) from 0.1 mol/L phosphate buffer solution (pH 7.0). Among the three phenothiazies, the poly(TB) film-modified CF exhibited an excellent electrocatalytic activity for the oxidation of nicotinamide adenine dinucleotide reduced form (NADH) at +0.2 V vs. Ag/AgCl. The poly(TB) film-modified CF was successfully used as working electrode unit of highly sensitive amperometric flow-through detector for NADH. The peak currents (peak heights) were almost unchanged, irrespective of a carrier flow rate ranging from 2.0 to 4.1 mL/min, resulting in the measurement of NADH (ca. 30 samples/hr) at 4.1 mL/min. The peak current responses of NADH showed linear relationship over the concentration range from 1 to 30 micromol/L (sensitivity: 0.318 microA/(micromol/L); correlation coefficient: 0.997). The lower detection limit was found to be 0.3 micromol/L (S/N = 3).

Electrochemical behavior of pyrroloquinoline quinone immobilized on silica gel modified with zirconium oxide

Pyrroloquinoline quinone (PQQ) was immobilized on the silica gel surface modified with zirconium oxide, designated as Si:Zr, by the carboxylic groups of the PQQ molecule and the zirconium oxide on the silica surface. The electrochemistry of PQQ immobilized on the Si:Zr matrix, incorporated in a carbon paste electrode, was evaluated using the cyclic voltammetry technique. The Si:Zr:PQQ-modified electrode showed a redox couple at E(m)=(E(pa1)+E(pc))/2=-0.150 V vs SCE at pH 7, close to that observed in aqueous solution, and another oxidation peak, E(pa2)=-0.100 V vs SCE. Studies in different pH solutions in the range of 3-7 showed that the first oxidation peak, E(pa1), is highly dependent on the solution pH shifting from to -0.175 to 0.100 V vs SCE, while E(pa2) remains practically constant at 0.100 V as the pH decreases from 7 to 3. The immobilized PQQ electrode presented the property to electrocatalyze the NADH at 150 mV vs SCE. The effect of addition of Ca(2+) ions on the electrode electroactivity for the NADH oxidation was also verified. Different from that observed for the PQQ immobilized on other electrode materials, the Ca(2+) ions did not influence the electrocatalytical response; however, the electrode stability was considerably improved in the presence of Ca(2+) ions, indicating that the matrix surface has a great influence on the electrochemical behavior of PQQ.

A new interference-free lysine biosensor using a non-conducting polymer film

An electrochemical biosensor for the determination of lysine to be used for rapid evaluation of food quality has been developed. Platinum electrodes have been coated by electropolymerisation with 1,2-diaminobenzene (1.2-DAB) using cyclic voltammetry. The reduction in the oxidation of interferents compared with the bare platinum electrode was 100% for ascorbic acid, 99% for acetaminophen and 99% for cysteine. The enzyme L-lysine-alpha-oxidase was then immobilised onto the polymer layer by passive adsorption and a calibration curve for lysine constructed. This gave a linear range of 1 x 10(-5) mol/l to 1 x 10(-3) mol/l and a limit of detection of 2 x 10(-7) mol/l.