Yeast modifies the nonlinear behavior of the electrode electrolyte interface under high voltage stimulation

In non-linear dielectric spectroscopy of yeast suspensions, previous studies distinguished nonlinear interface behavior from yeast membrane-induced currents by comparing power spectra of solutions with and without yeast. However, this method might be inaccurate because the effect of yeast can not be considered merely an additive contribution. In fact, the presence of yeast on the electrode surface can alter the voltage drop reaching the electrode, thus changing the nonlinear electrode response. No prior research has investigated the effect of yeast presence on the electrode surface using a nonlinear mathematical model. Here, we used a four-electrode system to record responses from solutions when applying a single-frequency voltage of 23 Hz. Using the Butler-Volmer model, we showed that yeast presence elevates a model parameter affected by ion concentration at the interface or mass transfer to the electrode. Model results suggest that the increase in the third harmonic, contrary to previous assumptions, may not be entirely attributed to the ionic current of the yeast membrane's proton pump. Our results are significant for distinguishing the biological effects of cells in the solution from the interface effects. It can also be used for online monitoring of cell growth in the environment.