MEDIATED AMPEROMETRIC DETECTION OF GLUCOSE-6-PHOSPHATE-DEHYDROGENASE AT A POLY(VINYL CHLORIDE) COVERED ELECTRODE USING 1,4-BENZOQUINONE ANDDIAPHORASE

Reduced nicotinamide adenine dinucleotide (NADH), produced from glucos e-6-phosphate dehydrogenase (G6PDH) was catalytically oxidized using d iaphorase and 1,4-benzoquinone to yield 1,4-hydroquinone. This benzoqu inone redox mediator was readily detected at an electrode polarized at +0.5 V (vs. Ag/AgCl) so avoiding the high overpotentials required for a direct electrochemical measurement of NADH. Also, the lipophilic na ture of the hydroquinone enabled a novel high selectivity plasticized PVC membrane mounted over the electrode to be exploited. The mediator/ PVC combination achieved NADH calibration linear up to at least 100 mu M. When used to assay G6PDH activity, a linear calibration from O.1-1 .0 U/mL was produced. The detection system offers the possibility of h ighly selective measurement of dehydrogenase enzyme activity in biolog ical samples without sample preparation and could provide the basis fo r simplified homogeneous immunoassays as well as dehydrogenase amperom etric enzyme electrodes.