Tuning Channel Architecture of Interdigitated Organic Electrochemical Transistors for Recording the Action Potentials of Electrogenic Cells

Organic electrochemical transistors (OECTs) have emerged as versatile electrophysiological sensors due to their high transconductance, biocompatibility, and transparent channel material. High maximum transconductances are demonstrated facilitating the extracellular recording of signals from electrogenic cells. However, this requires large channel dimensions and thick polymer films. These large channel dimensions lead to low transistor densities. Here, interdigitated OECTs (iOECTs) are introduced, which feature high transconductances at small device areas. A superior device performance is achieved by systematically optimizing the electrode layout regarding channel length, number of electrode fingers and electrode width. Interestingly, the maximum transconductance (g_max) does not straightforwardly scale with the channel width-to-length ratio, which is different from planar OECTs. This deviation is caused by the dominating influence of the source–drain series resistance R_sd for short channel devices. Of note, there is a critical channel length (15 µm) above which the channel resistance R_ch becomes dominant and the device characteristics converge toward those of planar OECTs. Design rules for engineering the performance of iOECTs are proposed and tested by recording action potentials of cardiomyocyte-like HL-1 cells with high signal-to-noise ratios. These results demonstrate that interdigitated OECTs meet two requirements of bioelectronic applications, namely, high device performance and small channel dimensions.