A TRIPLE-STEP POTENTIAL WAVE-FORM AT ENZYME MULTISENSORS WITH THICK-FILM GOLD ELECTRODES FOR DETECTION OF GLUCOSE AND SUCROSE

Significant loss of activity of thick-film gold electrodes is observed when they are used for continuous amperometric detection of H2O2 in 0 .1 M sodium phosphate buffer and in serum samples. Triple-step potenti al waveforms are utilized for pulsed amperometric detection to clean t he surface of conventional electrodes from poisoning substances and re activate them, thus maintaining uniform electrode activity. This techn ique is applied to a microprocessor-controlled multichannel sensor sys tem with poly(vinylacetate)-based enzyme membranes, which are attached to the thick-film gold electrodes by adhesion. The parameters of a tr iple-step potential sequence, which are dependent on the electrochemic al behaviour of the membrane-coated thick-film gold electrodes, have b een determined so that efficient cleaning of the electrode surfaces is obtained and at the same time the characteristics of the enzyme senso rs are not influenced. The potential sequence consists of an oxidation potential of 800 mV, a reduction potential of 100 mV and the detectio n potential of 600 mV (versus Ag/AgCl) for hydrogen peroxide. The trip le-step potential waveform is applied to the multichannel system for s imultaneous determination of glucose and sucrose in buffered aqueous s olutions and for detection of glucose in serum samples. A sensor respo nse with improved sensitivity and reproducibility is obtained. With th e on-line cleaning of the electrode surfaces by application of the tri ple-step potential waveform, uniform electrode activity is maintained even when the glucose sensors are operated in serum samples. The senso r response, obtained with continuous amperometric detection, proves to be limited by adsorption processes of H2O2 at the surface of the thic k-film gold electrodes. On the other hand, the sensor response obtaine d with application of the triple-step potential waveform indicates lim itation by diffusion processes and the upper limit of the linear range is extended from 5 to 12 mM for glucose and from 4 to 15 mM for sucro se in aqueous solutions.