Real-time monitoring of immobilized single yeast cells through multifrequency electrical impedance spectroscopy.

We present a microfluidic device, which enables single cells to be reliably trapped and cultivated while simultaneously being monitored by means of multifrequency electrical impedance spectroscopy (EIS) in the frequency range of 10 kHz-10 MHz. Polystyrene beads were employed to characterize the EIS performance inside the microfluidic device. The results demonstrate that EIS yields a low coefficient of variation in measuring the diameters of captured beads (~0.13%). Budding yeast, Saccharomyces cerevisiae, was afterwards used as model organism. Single yeast cells were immobilized and measured by means of EIS. The bud growth was monitored through EIS at a temporal resolution of 1 min. The size increment of the bud, which is difficult to determine optically within a short time period, can be clearly detected through EIS signals. The impedance measurements also reflect the changes in position or motion of single yeast cells in the trap. By analyzing the multifrequency EIS data, cell motion could be qualitatively discerned from bud growth. The results demonstrate that single-cell EIS can be used to monitor cell growth, while also detecting potential cell motion in real-time and label-free approach, and that EIS constitutes a sensitive tool for dynamic single-cell analysis.