Modified microelectrode interfaces for in-line electrochemical monitoring of ethanol in fermentation processes

An in-line, reagentless, electrochemical sensor for monitoring ethanol formation during fermentation processes has been constructed. The sensor is based on pulsed amperometic detection using platinum microelectrode arrays modified with poly-l-lysine and a PVC overlaying membrane. By using this configuration, problems associated with pH dependency of ethanol oxidation and interference from electroactive sugars were addressed. The poly-l-lysine/PVC modified electrode had a linear detection range of 0–12% (v/v) ethanol in phosphate buffer solutions (pH 3–5). The poly-l-lysine layer was thought to contribute to the pH independent ethanol response by providing interfacial buffering at the electrode surface. When ethanol measurements were performed in the presence of yeast cells the sensor became reversibly fouled. However, this problem was overcome by substituting the PVC membrane with hydrophilic poly(phenyl ether sulphone) (PES). The PES modified microarray had a linear detection range up to 10% (v/v). Selectivity of ethanol (0–14% v/v) over glucose (500 mM) is described. The sensor was stable when submerged in a wine fermentation vessel over a 30-day-period with negligible calibration drift being observed. The thermal stability of the PES membrane would enable the sensor to be heat sterilised in accordance with clean in-place regimes.