The Organic Electrolyte-gated Transistor's Biosensor Research

Organic field effect transistors?OFETs? have many advantages, such as low-cost, flexibility, easy preparation and biocompatibility, thus have extensive application prospects in fields of biomedical sensing. Electrolyte-gated organic field-effect transistors?EG-OFETs? have intrinsic signal amplification capability of field effect transistors?high sensitivity?; in addition, they can achieve specific detections through modification of chemical and biological groups. Biosensors based on EG-OFET structures have made considerable progress in detections of glucose, protein, and DNA. However, little work has been reported to study the intrinsic operation mechanisms of EG-FET biosensors, such as interactions between charge carriers, ions and water dipoles, this will hinder their further development. In this paper, we use impedance spectroscopy and voltammetry techniques combining with theoretical models to investigate the charge transport properties of the interfacial between organic semiconductor and liquid electrolyte in EGOFETs. More importantly, we successfully developed high-sensitivity sensors for ion-concentration detections based on EG-OFET structures. Main work can be summarized as follows:1. Developing EG-OFETs based on poly?3-hexylthiophene??P3HT?, transfer and output characteristics were investigated, respectively. The results show that compared to conventional OFETs, the work voltage?¹V? of our device is reduced to an order of magnitude. It also exhibits pronounced on-off ratio?>104?.2. Systematically studying different charge transport properties of EG-OFET devices with different active layers, such as homojunction and heterojunction systems. The results show that the device with the heterojunction structure has more obvious hysteresis effect, we confirm that this phenomenon is attributed that in the heterojunction system, the molecular arrangement of P3 HT is destroyed by PC₇₁ BM, leading to easier penetration of ion into the bulk organic semiconductors thus electrochemical doping effect.3. Using impedance spectroscopy and an equivalent circuit model to study the impedance characteristics of the EG-OFET devices. It reveals that the device operates mainly in the electric-double layer mode accompanying with the field-effect. We also thoroughly analyzed the electric double-layer characteristics between solid-liquid interfaces by Grahame's model, and demonstrate that the impedance of the EG-OFET device gradually decreased with the increased gate voltage.4. Successfully developing ion-detecion sensors based on the EG-OFET with low-cost, high-sensitivity, and detections of different ion concentration?K⁺ and Na⁺?. The sensitivities of K ⁺ and Na ⁺ are 10^-6mol/L and 10^-8mol/L, respectively. It is worth noting that the sensitivity of the sensor for Na⁺ concentration detection shows two orders of magnitude higher than currently reported best ion-sensitive sensor.