Galvanic decoupled sensor for monitoring biomass concentration during fermentation processes

A new sensor for monitoring the active biomass during fermentation processes is presented, which determines the electrical impedance without any contact of the electrodes to the liquid cell solution. The metal electrodes are covered by a non-conductive polymer layer. An AC current is induced in the cell solution by a capacitive coupling with no electrochemical reactions on the electrodes. The decoupled measurement allows acquiring the complex impedance of the cell solution with only one pair of electrodes and without any influence of electrical double-layer effects. The sensor electrodes are fabricated on a FR4-board and covered by a polyparaxylylene (Parylene-C) layer. The performance of the sensor is tested successfully by using the model culture system yeast Hansenula Polymorpha in the culture medium YPG. The sensor is able to monitor the biomass concentration and the metabolism of the growing culture.