On-Site Amplification of Neural Signals by Organic Field-Effect Transistors

In the field of brain-computer interface, the transducing elements play a pivotal role in monitoring and recording neural signals. Compared to noise-sensitive microelectrodes, the high transconductance of organic electrochemical transistors enables on-site signal amplification, leading to an enhanced signal-to-noise ratio (SNR). However, the ion exchange process restricts its capability to record high-frequency (&gt; 1 kHz) neural signals. Although lack of direct communication with the ions in the body, organic field-effect transistors (OFETs) exhibit not only high transconductance (up to 1 mS), low sensitivity to noise (down to 1 nA), and remarkable mechanical flexibility but also high operating speed (&gt; 10 kHz). These combined merits may broaden the potential for full-frequency brain signals recording using active electrodes.<br/>In this study, we developed an ultra-conformal OFETs (5 µm channel length) featuring a top-gate bottom-contact structure, achieving a transconductance of 100 µS and a cut-off frequency of 10 kHz. In comparison to microelectrodes (SNR = 10 dB), the electrocorticogram signals amplified by OFETs exhibit a superior SNR (over 50 % improvement) and an enhanced temporal resolution. The pre-ictal brain signals (500 µV) associated with epilepsy are effectively monitored by our OFETs array. With proper encapsulation, the devices demonstrate excellent stability and biocompatibility. We believe that the flexible organic active electrode paves a promising path for disease prediction and high-frequency neural signals recording.