Impedance spectra of patch clamp scenarios for single cells immobilized on a lab-on-a-chip

A simple method based on impedance spectroscopy (IS) was developed to distinguish between different patch clamp modes for single cells trapped on microapertures in a patch clamp microchannel array designed for patch clamping on cultured cells. The method allows detecting via impedance analysis whether the cell membrane is ruptured (and culturing prevented) or the cell is still in the attached mode. A modular microfluidic lab-on-a-chip device based on planar patch clamp technology was used to capture multiple individual cells on an array of microapertures. The comparison of the measured and simulated impedance spectra proved that the presented method could distinguish between a cell-attached mode and a whole-cell mode even with low-quality seals. In physiological conditions, the capacitance of HeLa cells was measured to similar to 38 pF. The first gigaseal was recorded and maintained for 40 min. Once whole-cell configurations were established, trapped cells were superfused with a 140 mM KCl aqueous solution: the change in the measured cell impedance revealed a capacitance decrease to similar to 27.5 pF that could be due either to a change in the cell size or to the reduced charge separation across the cell membrane. After incubating the chip for 24 h, HeLa cells adhered and grew on the chip surface but did not survive when trapped on the microapertures. The microfluidic system proved to work as a micro electrophysiological analysis system, and the IS-based method can be used for further studies on the post-trapping strength of the seal between the microapertures and the trapped cells to be cultured.