Recent research demonstrates the viability of organic electrochemical transistors (OECTs) as an emergent technology for biosensor applications. Herein, a comprehensive summary is provided, highlighting the significant progress and most notable advances within the field of OECT‐based biosensors. The working principles of an OECT are detailed, with specific attention given to the current library of organic mixed ionic‐electronic conductor (OMIEC) channel materials utilized in OECT biosensors. The application of OECTs for metabolite, ion, neuromorphic, electrophysiological, and virus sensing as well as immunosensing is reported, detailing the breadth and scope of OECT‐based biosensors. Furthermore, an outlook and perspective on synthetic molecular design of future channel materials, specifically designed for OECT biosensors, is provided. The development of optimized channel materials, creative device architectures, and operational nuances will set the stage for OECT‐based biosensors to thrive and accelerate their clinical prevalence in the near future.

Organic Electrochemical Transistors: An Emerging Technology for Biosensing

This review is written to introduce infrared photon detectors based on solution-processable semiconductors. A new generation of solution-processable photon detectors have been reported in the past few decades based on colloidal quantum dots, two-dimensional materials, organics semiconductors, and perovskites. These materials offer sensitivity within the infrared spectral regions and the advantages of ease of fabrication at low temperature, tunable materials properties, mechanical flexibility, scalability to large areas, and compatibility with monolithic integration, rendering them as promising alternatives for infrared sensing when compared to vacuum-processed counterparts that require rigorous lattice matching during integration. This work focuses on infrared detection using disordered semiconductors so as to articulate how the inherent device physics and behaviors are different from conventional crystalline semiconductors. The performance of each material family is summarized in tables, and device designs unique to solution-processed materials, including narrowband photodetectors and pixel-less up-conversion imagers, are highlighted in application prototypes distinct from conventional infrared cameras. We share our perspectives in examining open challenges for the development of solution-processable infrared detectors and comment on recent research directions in our community to leverage the advantages of solution-processable materials and advance their implementation in next-generation infrared sensing and imaging applications.

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Solution-processable infrared photodetectors: Materials, device physics and applications

Photonic (bio)electronic circuits and devices have been an enduring goal in modern photonics and electronics. Organic photoelectrochemical transistor (OPECT) interfacing light with biological world creates a substantial opportunity to this end due to the immense light−bio−matter interplay. Through modulating the invisible ionic circuit of organic electrochemical transistor (OECT) with a bipolar electrode (BPE) accommodating different semiconductor combinations, the unique photonic electronics toward logic and sensor applications are realized. Six combinations of BPEs are produced by the representative n‐type CdS/TiO2 and p‐type BiOI/NiO semiconductors, and the corresponding photonic characteristics and operation rationale are systematically investigated and explained. Designation of opto‐logic circuits and feasibility as a sensory platform are subsequently demonstrated. This work not only represents new photonic bioelectronics but also provides a generic mechanism for the design and development of advanced opto‐logics and bio‐analytics.

Bipolar Modulation of the Ionic Circuit for Generic Organic Photoelectrochemical Transistor Logic and Sensor

Non-intrusive sensors that can be attached to marine species offer opportunities to study the impacts of environmental changes on their behaviors and well-being. This work presents a thin, flexible sensor tag to monitor the effects of dissolved oxygen and salinity on bivalve gape movement. The measurement range studied was 0.5-6 ppm for the dissolved oxygen sensor and 4-40 g kg-1 for the salinity sensor. The curvature strain sensor based on electrodeposited semiconducting fibers enabled measurements of an oyster's gape down to sub-mm displacement. The multiplexed sensors were fabricated by low-cost techniques, offering an economical and convenient platform for aquaculture studies.

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Multiplexed printed sensors for in situ monitoring in bivalve aquaculture.

In this work, we synthesized the single-crystalline square BiOCl nanosheets with oxygen vacancies via the facile solvothermal route. The prepared BiOCl nanosheets were deposited on a tapered microfiber as a saturable absorber. Via the evanescent filed interaction with the BiOCl saturable absorber, a soliton mode-locked Er-doped fiber laser was demonstrated for the first time, producing a pulse duration of 990 fs at a central wavelength of 1563 nm with a FWHM bandwidth of 3.2 nm. The signal-to-noise ratio was 36 dB at the fundamental repetition rate of 7.9 MHz. Our results confirmed that the BiOCl nanosheets with abundant oxygen vacancies could be applied for the ultrafast photonics. 

Single crystalline BiOCl nanosheets with oxygen vacancies for ultrafast mode-locking operation

With our marine ecosystems under threat from climate change, there is an urgent need to continuously monitor marine conditions. One key indicator is the dissolved oxygen level, but existing sensors are limited by size and costs that preclude widespread non-intrusive monitoring. This work reports a new dual-gate design based on organic electrochemical transistors (OECTs) to track dissolved oxygen concentration in seawater, a highly challenging matrix owing to its high ionic strength and multitude of chemical interferents. We present the novel operating principle, by deriving the channel conductance with respect to potentials on the two gates. The sensor achieved a detection limit of 0.5 ppm dissolved oxygen concentration in seawater. The device demonstrated reliable operation over five days and was capable of monitoring oxygenation changes arising from the photosynthesis cycles of saltwater macro-algae.

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Shuo En Wu

Papers

Dual-Gate Organic Electrochemical Transistors for Marine Sensing