All‐Polymer Fiber Organic Electrochemical Transistor for Chronic Chemical Detection in the Brain

Abstract Continuous and precise monitoring of chemicals in the brain can assist in understanding the working mechanism of the brain and exploring therapeutics for nerve disorders. Organic electrochemical transistors (OECTs) are employed for this purpose due to their high sensitivity from the in situ amplification effect. However, the chronic and stable detection of chemicals in the brain is rarely reported for OECTs. It is possibly due to the chronic inflammation from mechanical mismatch between the device and soft brain tissue as well as the biofouling that hinder the diffusion of chemicals to decrease the sensitivity similar to other implanted devices. Therefore, an all‐polymer fiber OECT (PF‐OECT) is designed, composed solely of conductive polymers and fluorine rubber. The PF‐OECT shows matching modulus with the soft brain tissue and good anti‐biofouling performance. It also demonstrates both high sensitivity and electrochemical stability under dynamic deformations and in complex protein solutions. Finally, the PF‐OECT is implanted into the mouse brain, achieving a stable 14‐day ascorbic acid monitoring. The design strategy of PF‐OECT presents a potential avenue for developing more biomedical devices.