In-situ biomass characterisation by impedance spectroscopy using a full-bridge circuit

A full-bridge sensor system for characterising biosuspensions by impedance spectroscopy which avoids cross-sensitivity to temperature is presented. To record a large range of different kinds of cells, frequency is varied between 500 kHz and 50 MHz. The characteristic frequencies of the #-polarisation of animal cells (mouse), yeasts (Saccharomyces cerevisiae) and Escherichia coli bacteria are located in this range. The widespread applicability of this method is demonstrated by measurements on suspensions of different cells and the determination of concentration in a fermentation process. Furthermore, yeast suspensions are characterised at temperatures between T₁=24°C and T₂=36°C to evaluate the influence of temperature. A reduction of cross-sensitivity of about one order of magnitude compared to a single-sensor results. Changing in the conductivity of the suspension by 26% alters the measured biomass concentration by only 2.8%.