Development of a four electrode sensor array for impedance spectroscopy in high content screenings of fermentation processes

There is an increasing demand of efficient screening techniques with high information output in biotechnological research and pharmaceutical industry. One effective method of monitoring biological cultures is the electrical impedance spectroscopy. In this work an integrated sensor array consisting of a four electrode sensor design on polyimide flextape in 96 well microtiter plates (MTPs) is characterised. FEM-simulations and measurements of different electrode designs are compared and show good agreement. Circular shaped electrodes are identified as optimal designs with stable signals even at high shaking frequencies. These high frequencies of at least 1000 rpm are necessary to provide high oxygen transfer in microbial cultivations. Fermentations in the MTPs were carried out with Hansenula polymorpha and Escherichia coli in filling volumes of 100–200 μL. The measured data of conductance and capacitance are shown and discussed in comparison to a reference signal obtained by a BioLector measurement system (m2p-labs GmbH, Germany). Biological phenomena, e.g. the change of carbon source of E. coli from glycerol to proteins can clearly be identified by analysing the measured capacitance and conductance during the fermentation.