High-Performance Biosensors Based on Solution-Gated Organic Thin Film Transistors
Authors: Liao Caizhi , Yan Feng 
Published: February 2020

Solution-gated transistors have shown promising applications in biosensors due to the high sensitivity, low working voltage and the simple design of the devices. Solution-gated transistors normal have no gate dielectric and the gate voltages are applied directly on the solid/electrolyte interfaces or electric double layers near the channel and the gate, which lead to very low working voltages (about 1 V) of the transistors. On the other hand, the devices can be easily prepared by solution process or other convenient methods because of the much simpler device structure compared with that of a conventional field effect transistor with several layers. Many biosensors can be developed based on the detection of potential changes across solid/electrolyte interfaces induced by electrochemical reactions or interactions. The devices normally can show high sensitivity due to the inherent amplification function of the transistors. Here, I will introduce several types of biosensors studied by our group recently, including DNA, glucose, dopamine, uric acid, cell, and bacteria sensors, based on solution-gated organic electrochemical transistors.[1] The biosensors show high sensitivity and selectivity when the devices are modified with functional nano-materials (e.g. graphene, Pt nanoparticles) and biomaterials (e.g. enzyme, antibody, DNA) on the gate electrodes or the channel. Furthermore, the devices are miniaturized successfully for the applications as sensing arrays. It is expected that the solution-gated organic transistors will find more important applications in the future. Some representative works are presented as follows.
Figure 1 shows an organic electrochemical transistor (OECT) based on poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid) (PEDOT:PSS) integrated in a flexible microfluidic system. [2] We find that the device performance is not influenced by the bending status of the device. A novel label-free DNA sensor is developed using the OECT with single-stranded DNA probes immobilized on the gate electrode. The device can successfully detect a complementary DNA target down to 1 nM. The detection limit is extended to 10 pM by pulse-enhanced hybridization process of DNA in the microfluidic channel. Therefore OECTs are excellent candidates for flexible and low-cost biosensors.
Figure 2 shows the applications of flexible OECTs with functionalized gate electrodes as highly selective and sensitive enzyme biosensors for the detections of uric acid, cholesterol and glucose. [3] Many other types of enzyme biosensors can be realized based on the same principle. The devices were then successfully used for the selective detections of uric acid level and glucose level in saliva, which renders the devices promising transducers for noninvasive detections of biomarkers in human body.
Reference:

Caizhi Liao, Meng Zhang, Mei Yu Yao, Tao Hua, Li Li, Feng Yan, Adv. Mater. 27, 7493-7527 (2015).

Peng Lin, Xiaoteng Luo, I-Ming Hsing and Feng Yan, Adv. Mater. 23, 4035-4040 (2011).

Caizhi Liao, Chunhin Mak, Meng Zhang, Helen L.W. Chan and Feng Yan, Adv. Mater. 27, 676-681 (2015).

Figure 1