This review summarizes and highlights the current state-of-the-art of research on chemical sensors and biosensors in liquid environment and neuromorphic devices based on electrolyte-gated organic transistors with the active semiconductor layer of organic π-conjugated materials (small molecules, oligomers and polymers). The architecture and principles of operation of electrolyte-gated organic transistors and the main advantages and drawbacks of these devices are considered in detail. The criteria for the selection of organic semiconductors for these devices are presented. The causes of degradation of semiconductor layers and ways of their elimination are discussed. Examples of the use of electrolyte-gated organic transistors as bio and chemical sensors, artificial synapses and computing devices are given. The bibliography includes 132 references.

Requirements of speed and simplicity in testing stimulate the development of modern biosensors. Electrolyte-gated organic field-effect transistors (EGOFETs) are a promising platform for ultrasensitive, fast, and reliable detection of biological molecules for low-cost, point-of-care bioelectronic sensing. Biosensitivity of the EGOFET devices can be achieved by modification with receptors of one of the electronic active interfaces of the transistor gate or organic semiconductor surface. Functionalization of the latter gives the advantage in the creation of a planar architecture and compact devices for lab-on-chip design. Herein, we propose a universal, fast, and simple technique based on doctor blading and Langmuir–Schaefer methods for functionalization of the semiconducting surface of C8-BTBT-C8, allowing the fabrication of a large-scale biorecognition layer based on the novel functional derivative of BTBT-containing biotin fragments as a foundation for further biomodification. The fabricated devices are very efficient and operate stably in phosphate-buffered saline solution with high reproducibility of electrical properties in the EGOFET regime. The development of biorecognition properties of the proposed biolayer is based on the streptavidin–biotin interactions between the consecutive layers and can be used for a wide variety of receptors. As a proof-of-concept, we demonstrate the specific response of the BTBT-based biorecognition layer in EGOFETs to influenza A virus (H7N1 strain). The elaborated approach to biorecognition layer formation is appropriate but not limited to aptamer-based receptor molecules and can be further applied for fabricating several biosensors for various analytes on one substrate and paves the way for “electronic tongue” creation.

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Selective analysis of CO gas, hydrogen and hydrogen sulfide was carried out using single metal oxide sensor. Non-stationary sensor heating mode allowed discovering individual peculiarities of each gas in question. Resistance vs. time curves were converted into multidimensional data arrays and processed by chemometrics methods; as a result, qualitative and quantitative analysis of single-component gas systems was successfully carried out.

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Electrolyte-gated organic field-effect transistors (EGOFETs) is a popular platform for numerous sensing and biosensing applications in aqueous media. In this work, the variation of electrical characteristics of EGOFETs based on small-molecule organic semiconductor C8-BTBT and polystyrene blend in water solutions at different pH values was investigated. A positive shift of the threshold voltage with near-Nernstian pH sensitivity was demonstrated in the pH range from 4.9 to 2.8, while no measurable pH dependence in the range from 4.9 to 8.6 pH was registered. These results indicate chemical doping of the molecules of organic semiconductors by protons from the electrolyte in the acidic region. In order to check the applicability of the EGOFETs in a flow mode, a flow chamber was designed and assembled. The preliminary results obtained in the flow mode measurements showed a fast response to pH variation.

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