Versatile Sensing Platform Assemble on Flexible Organic Transistors
Authors: Liao Caizhi , Yan Feng 
Published: February 2020

Organic thin-film transistors (OTFTs), as the essential parts of modern electronic devices, have found a wide range of application paradigms in low-cost radio frequency identification (RFID), large-area display and portable high-performed sensors. Being an important type of the OTFTs family, organic electrochemical transistors(OECTs) demonstrate high stability in aqueous electrolytes for long time, making it promising for the real-time chemical and biological sensing applications in electrolytes. Considering these desirable properties, OECTs have been extensively investigated as a feasible platform for a wide range of sensing scenarios, including ions, glucose, uric acid, dopamine, DNA, bacteria and cells, etc. Nevertheless, these thoroughly investigated OECTs sensors are solely fabricated on the conventional planar structures (silicon wafer, glass, and PET, etc), making it difficult to be integrated with the flexible and wearable electronic systems. To alleviate this problem, Olle Inganäs et al reported a novel approach for the construction of fiber-based OECTs assembled on the textile monofilaments with 10–100 μm diameters. The flexible woven electrochemical transistors demonstrate fast switching time and therefore represent a significant step towards the realization of electronic textiles. However, no functionalized fiber OECTs devices have ever been investigated for the high performance biological sensing applications. Up until now, it is still tricky to deal with the fabrication and functionalization of fiber-based OECTs device for sensing applications.

To alleviate the challenge, we hereby report for the first time, the fabrication and functionalization of fiber-based OECTs as a versatile sensing platform for high-performed biological sensors. The fiber OECTs exhibit high electric conductivity, mechanical flexibility and extremely light weighted. Different form their conventional planar counterparts, these weavable fiber-based OECT devices demonstrate ultrahigh flexibility, making it a potential candidate for the realization of cutting-edge wearable electronics. The functionalized devices were successfully fabricated for various chemical and biological sensing scenarios, including pH, metal ions, glucose, dopamine and uric acid. igh performance fiber-based OECT glucose sensor was realized by the using of functionalized CHIT-graphene flakes/GOx/Pt fiber gate electrode. The low detection limit of the device to glucose was about 30nM. Similarly, flexible fiber OECT dopamine sensor and uric acid sensor could also been fabricated using the modified fiber gate Nafion (1.0%)–graphene/Pt and UOx/PANI/Nafion-graphene/Pt, respectively. The detection limit of these sensors was as low as several to a few tens nM, which was approximately 2-3 orders of magnitude lower than the conventional electrochemical approaches. Meanwhile, desirable selectivity property could be achieved through the proper modification of the gate electrode. The sensitivity and selectivity features of these fiber based OECT sensors could be simultaneously enhanced by the proper co-modification of bio-molecules, biocompatible polymers and nano-materials on the surface of gate electrode. More interestingly, the flexible fiber-based OECTs afford for the no-invasive detection of biological elements in human saliva.

In summary, the successfully fabricated high-performance fiber-based OECT device holds great potential for a wide range of applications, including point-of-care tests, clinic diagnosis and therapy, fitness tracking and body-condition monitoring.