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 potential waveforms are utilized for pulsed amperometric detection to clean the surface of conventional electrodes from poisoning substances and reactivate them, thus maintaining uniform electrode activity. This technique is applied to a microprocessor-controlled multichannel sensor system with poly(vinylacetate)-based enzyme membranes, which are attached to the thick-film gold electrodes by adhesion. The parameters of a triple-step potential sequence, which are dependent on the electrochemical behaviour of the membrane-coated thick-film gold electrodes, have been determined so that efficient cleaning of the electrode surfaces is obtained and at the same time the characteristics of the enzyme sensors are not influenced. The potential sequence consists of an oxidation potential of 800 mV, a reduction potential of 100 mV and the detection potential of 600 mV (versus Ag/AgCl) for hydrogen peroxide. The triple-step potential waveform is applied to the multichannel system for simultaneous determination of glucose and sucrose in buffered aqueous solutions and for detection of glucose in serum samples. A sensor response with improved sensitivity and reproducibility is obtained. With the on-line cleaning of the electrode surfaces by application of the triple-step potential waveform, uniform electrode activity is maintained even when the glucose sensors are operated in serum samples. The sensor response, obtained with continuous amperometric detection, proves to be limited by adsorption processes of H2O2 at the surface of the thick-film gold electrodes. On the other hand, the sensor response obtained with application of the triple-step potential waveform indicates limitation 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 sucrose in aqueous solutions.