Part II. Potentiodynamic on-line monitoring of the concentration of glucose in metal-walled bioreactors

Electronics. steam-sterilized membranes and disposable sensors for the on-l ine monitoring of glucose in the 1-20 mM range are described. The problems addressed, in addition to those common with, and addressed earlier in the c ontext of, continuous amperometric in vivo monitoring of glycemia in diabet ic patients, derive From (a) the need to monitor the glucose concentration in the total absence of oxygen, Cb) the variation of the signal at low (I m M) glucose concentration with the partial pressure of oxygen when the senso r is based on the electrical connection (wiring) of glucose oxidase reactio n centers to an electrode through an electron conducting redox hydrogel and Cc) the safety related requirement to ground the stainless steel-walled in dustrial bioreactor electrically. We show that the effect of oxygen is elim inated upon shielding the glucose anode (poised at + 400 mV vs. Ag / AgCl) by a glucose permeable, gold-coated membrane cathode (poised at - 400 mV vs . Ag / AgCl). We also describe a novel and simple circuit allowing the use of the grounded reactor wall as the counter-electrode and the poising of th e nearby anode and cathode at their respective potentials. (C) 2000 Elsevie r Science B.V. All rights reserved.