Nonlinear dielectric spectroscopy of live cells using superconducting quantum interference devices

Magnetic detection of the nonlinear response of cell suspensions to oscillating electrical fields is reported. It has been shown that $H+$-ATPase, which is located in plasma membrane of yeast cells, generates harmonics of the fundamental frequency when electrically excited at certain frequencies and field strengths. Electrode polarization may cause erroneous results, especially when using a conventional four-probe setup. In this letter we use highly sensitive superconducting quantum interference device magnetometers to detect the cells’ nonlinear response and to avoid electrode polarization effects. Experiments were carried out using yeast (Saccharomyces cerevisiae, $108cells∕ml$⁠) cells with excitation voltages and frequencies between $1–5V∕cm$ and 10–300 Hz, respectively.