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1. A hybrid transistor with transcriptionally controlled computation and plasticity

   https://doi.org/10.1038/s41467-024-45759-1  

   Gao, Yang; Zhou, Yuchen; Ji, Xudong; Graham, Austin J; Dundas, Christopher M; Miniel_Mahfoud, Ismar E; Tibbett, Bailey M; Tan, Benjamin; Partipilo, Gina; Dodabalapur, Ananth; et al (December 2024, Nature Communications)

   Abstract Organic electrochemical transistors (OECTs) are ideal devices for translating biological signals into electrical readouts and have applications in bioelectronics, biosensing, and neuromorphic computing. Despite their potential, developing programmable and modular methods for living systems to interface with OECTs has proven challenging. Here we describe hybrid OECTs containing the model electroactive bacteriumShewanella oneidensisthat enable the transduction of biological computations to electrical responses. Specifically, we fabricated planar p-type OECTs and demonstrated that channel de-doping is driven by extracellular electron transfer (EET) fromS. oneidensis. Leveraging this mechanistic understanding and our ability to control EET flux via transcriptional regulation, we used plasmid-based Boolean logic gates to translate biological computation into current changes within the OECT. Finally, we demonstrated EET-driven changes to OECT synaptic plasticity. This work enables fundamental EET studies and OECT-based biosensing and biocomputing systems with genetically controllable and modular design elements. 

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2. Operation mechanism of organic electrochemical transistors as redox chemical transducers

   https://doi.org/10.1039/d1tc02224e  

   Tan, Siew Ting; Keene, Scott; Giovannitti, Alexander; Melianas, Armantas; Moser, Maximilian; McCulloch, Iain; Salleo, Alberto (January 2021, Journal of Materials Chemistry C)

   null (Ed.)

   The ability to control the charge density of organic mixed ionic electronic conductors (OMIECs) via reactions with redox-active analytes has enabled applications as electrochemical redox sensors. Their charge density-dependent conductivity can additionally be tuned via charge injection from electrodes, for instance in organic electrochemical transistors (OECTs), where volumetric charging of the OMIEC channel enables excellent transconductance and amplification of low potentials. Recent efforts have combined the chemical detection with the transistor function of OECTs to achieve compact electrochemical sensors. However, these sensors often fall short of the expected amplification performance of OECTs. Here, we investigate the operation mechanism of various OECT architectures to deduce the design principles required to achieve reliable chemical detection and signal amplification. By utilizing a non-polarizable gate electrode and conducting the chemical reaction in a compartment separate from the OECT, the recently developed Reaction Cell OECT achieves reliable modulation of the OECT channel's charge density. This work demonstrates that systematic and rational design of OECT chemical sensors requires understanding the electrochemical processes that result in changes in the potential (charge density) of the channel, the underlying phenomenon behind amplification. 

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3. A Highly Sensitive and Long‐Term Stable Wearable Patch for Continuous Analysis of Biomarkers in Sweat

   https://doi.org/10.1002/adfm.202306117  

   Lorestani, Farnaz; Zhang, Xianzhe; Abdullah, Abu Musa; Xin, Xin; Liu, Yushen; Rahman, Md Mashfiqur; Biswas, Md_Abu Sayeed; Li, Bowen; Dutta, Ankan; Niu, Zhenyuan; et al (December 2023, Advanced Functional Materials)

   Abstract Although increasing efforts have been devoted to the development of non‐invasive wearable electrochemical sweat sensors for monitoring physiological and metabolic information, most of them still suffer from poor stability and specificity over time and fluctuating temperatures. This study reports the design and fabrication of a long‐term stable and highly sensitive flexible electrochemical sensor based on nanocomposite‐modified porous graphene by facile laser treatment for detecting biomarkers such as glucose in sweat. The laser‐reduced and patterned stable conductive nanocomposite on the porous graphene electrode provides the resulting glucose sensor with an excellent sensitivity of 1317.69 µA mm⁻¹cm⁻²and an ultra‐low limit of detection of 0.079 µm. The sensor can also detect pH and exhibit extraordinary stability to maintain more than 91% sensitivity over 21 days in ambient conditions. Taken together with a temperature sensor based on the same material system, the dual glucose and pH sensor integrated with a flexible microfluidic sweat sampling network further results in accurate continuous on‐body glucose detection calibrated by the simultaneously measured pH and temperature. The low‐cost, highly sensitive, and long‐term stable platform could facilitate the early identification and continuous monitoring of different biomarkers for non‐invasive disease diagnosis and treatment evaluation. 

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4. Organic Electrochemical Transistors Based on Room Temperature Ionic Liquids: Performance and Stability

   https://doi.org/10.1002/pssa.201800631  

   Kaphle, Vikash; Liu, Shiyi; Keum, Chang-Min; Lüssem, Björn (October 2018, physica status solidi (a))

   Organic electrochemical transistors (OECTs) are becoming a key device in the field of organic bioelectronics. For many applications of OECTs, in particular for enzymatic sensing, a complex mixture of room temperature ionic liquids (RTILs) combined with other electrolytes is used as a gate electrolyte, making the interpretation of experimental trends challenging. Here, the switching mechanism of OECTs using such RTILs is studied. It shows that ions smaller in size than the ions contained in the RTIL (e.g., Na+) have to be added to the ionic liquid to ensure switching of the OECTs. Furthermore, it is shown that OECTs based on RTILs exhibit noticeable gate‐bias stress effects and a hysteresis in the electrical transfer characteristics. A model based on incomplete charging/discharging of the effective gate capacitance during operation of the OECT and a dispersion in the ion mobilities is proposed to explain these instabilities, and thus it shows that the hysteresis can be minimized by optimizing the geometry of the device. Overall, a better understanding of the underlying mechanisms of switching and stability of OECTs based on RTILs is the first step toward various applications such as lactate acid sensors and neurotransmitter recording. 

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5. Organic Electrochemical Transistors functionalized with Protein Minibinders for Sensitive and Specific Detection of SARS‐CoV‐2

   https://doi.org/10.1002/admi.202202409  

   Huang, Po‐Chun; Zhou, Ying; Porter, Erin B.; Saxena, Ravindra G.; Gomez, Andrea; Ykema, Matthew; Senehi, Naomi L.; Lee, Dongjoo; Tseng, Chia‐Ping; Alvarez, Pedro J.; et al (May 2023, Advanced materials interfaces)

   There is a need for rapid, sensitive, specific, and low-cost virus sensors. Recent work has demonstrated that organic electrochemical transistors (OECTs) can detect the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Here, a simple and low-cost approach to the fabrication of OECT devices with excellent stability and unprecedented sensitivity and specificity for the detection of SARS-CoV-2 virus is demonstrated. The devices rely on the engineered protein minibinder LCB1, which binds strongly to SARS-CoV-2. The resulting devices exhibit excellent sensitivity for the detection of SARS-CoV-2 virus and SARS-CoV-2 spike protein receptor binding domain (RBD). These results demonstrate a simple, effective, and low-cost biomolecular sensor applicable to the real-time detection of SARS-CoV-2 virus and a general strategy for OECT device design that can be applied for the detection of other pathogenic viruses. 

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