Polymer transistors for cell recordings
Tuning channel architecture of interdigitated organic electrochemical transistors for recording the action potentials of electrogenic cells
Challenge
Organic electrochemical transistors (OECTs) have emerged as versatile electrophysiological sensors due to their high transconductance, biocompatibility, and transparency. These devices use conducting polymers as channel material. The direct exchange of ions between the conducting polymer channel and electrolyte, which modulates the channel resistance, enables the extracellular recording of action potentials of electrogenic cells. However, therefore large channel dimensions and thick polymer films are required, which precludes high device integration. A high transistor density is required not only for sensing chemical signals from different locations of the chip (chemical imaging) but also to study the signal propagation in cell networks.
Approach
Yuanying Liang and her coworkers from the Technical University of Munich and the RWTH Aachen introduced interdigitated OECTs (iOECTs), which feature high transconductances at small device sizes, Figure a). Ms Liang systematically optimized the electrode layout regarding channel length, number of electrode fingers as well as electrode width and characterized the electrical performance of these devices.
Achievements
The researchers found that the maximum transconductance, which defines the device sensitivity, does not straightforwardly scale with the channel width-to-length ratio, which is different from planar OECTs. Ms Liang found out that this deviation from the classical behavior is caused by the dominating influence of the source-drain series resistance Rsd for short channel devices. Noteworthy, there is a critical channel length (15 µm), above which, the channel resistance Rch becomes dominant and the device characteristics converge towards those of planar OECTs, Figure b). Based on these observations, design rules were proposed by the researchers for tuning the performance of iOECTs. The optimized and highly integrated polymer transistors were tested by recording action potentials of cardiomyocyte-like HL-1 cells with high signal-to-noise ratio, Figure c). Furthermore, they could study the propagation action potential of connected cardiac cells as a function of drug administration, see contour map of activation times in Figure d). These results demonstrate that interdigitated OECTs meet two requirements of bioelectronic applications, namely high device performance and small channel dimensions.
Original publication: Liang, Y., Maybeck, V., Brings, F., Ingebrandt, S., Pich, A., Offenhäusser, A. Mayer, D. Tuning Channel Architecture of Interdigitated Organic Electrochemical Transistors for Recording the Action Potentials of Electrogenic Cells. Advanced functional materials, 29 (2019) 1902085. https://doi.org/10.1002/adfm.201902085
Contact:
Dr. Dirk Mayer
Institute of Complex Systems, Bioelectronics (ICS-8)
Tel.: +49 2461 61-4023
E-Mail: dirk.mayer@fz-juelich.de