REAGENTLESS CHEMICALLY-MODIFIED CARBON-PASTE ELECTRODE BASED ON A PHENOTHIAZINE POLYMER DERIVATIVE AND YEAST ALCOHOL-DEHYDROGENASE FOR THE ANALYSIS OF ETHANOL

Amperometric biosensors for ethanol were constructed by immobilizing yeast alcohol dehydrogenase (ADH) on carbon paste (graphite powder: paraffin oil) chemically modified with a polymer to which a necessary mediator for electrocatalytic NADH oxidation had been covalently attached. Three different approaches were tested: adsorption of ADH on the electrode surface and adding NAD+ to the contacting buffer; having both ADH and NAD+ mixed into the paste; and co-immobilizing ADH and NAD+ in the paste by adding polyethylenimine to the reaction mixture. The last approach resulted in the highest and fastest response. When inserted into a flow injection system, the biosensor responded linearly to ethanol between 2 muM and 3 mM. The biosensor operates at +100 mV vs. Ag/AgCl.