Monitoring of cell layer coverage and differentiation with the organic electrochemical transistor

Electrical, label-free monitoring of cells is a non-invasive method for dynamically assessing the integrity of cells for diagnostic purposes. The organic electrochemical transistor (OECT) is a device that has been demonstrated to be advantageous for interfacing with biological systems and had previously been shown to be capable of monitoring electrically tight, resistant, barrier type tissue. Herein, the OECT is demonstrated not only for monitoring of barrier tissue cells such as MDCK I, but also for other, non-barrier tissue adherent cells including HeLa cells and HEK epithelial cells. Transistor performance, expressed as transconductance (g_m) is measured as a function of frequency; barrier tissue type cells are shown to have a more abrupt drop in transconductance compared to non-barrier tissue cells, however both tissue types are clearly distinguishable. Simple modelling of the cell layers on the transistor allows extraction of a resistance term (R_c). OECT monitoring shows that barrier tissue cells lose their barrier function in a standard calcium switch assay, but remain adhered to the surface. Re-addition of calcium results in recovery of barrier tissue function. The entire process is continuously followed both electronically and optically. Finally, high resolution fluorescence imaging of live cells labelled with a red fluorescent actin marker demonstrates the versatility of this method for tracking molecular events optically, with direct correlation to electronic readouts.