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-line 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 context of, continuous amperometric in vivo monitoring of glycemia in diabetic patients, derive from (a) the need to monitor the glucose concentration in the total absence of oxygen, (b) the variation of the signal at low (1 mM) glucose concentration with the partial pressure of oxygen when the sensor is based on the electrical connection (wiring) of glucose oxidase reaction centers to an electrode through an electron conducting redox hydrogel and (c) the safety related requirement to ground the stainless steel-walled industrial bioreactor electrically. We show that the effect of oxygen is eliminated 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 the nearby anode and cathode at their respective potentials.