Electrochromic analog control based on Organic Electrochemical Transistors and driven by dopamine sensing at the gate electrode

The growing interest in developing bio-inspired technologies aims to provide fast-responsive, wearable and smart devices that can emulate biological systems.1 However, the current devices are unable to successfully induce the chemical stimuli that characterize biological synapses, while they rely on electrical signals. To address this issue, we investigated the role of Organic Electrochemical Transistors (OECTs) in a system comprehensive of sensing, computing and actuating phases. The analogical control system is driven by dopamine sensing, that is obtained through the analyte oxidation by applying a positive potential, above +0.2 V, at the gate electrode.2 The device functions by forcing a fixed current (Id) at the drain, thereby generating potential variations at the drain electrode, correlated to dopamine concentration. The modulation is determined by the transistor architecture, in which the channel is made of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in its conductive state. These devices typically operate in depletion mode, where the application of gate voltage progressively reduces the conductivity of the PEDOT:PSS channel by depleting charge carriers from the polymer matrix. Redox-active species, such as dopamine, initiate a cascade of redox processes that result in PEDOT reduction, thereby increasing its electrical resistance and modulating Vd under a fixed Id condition. Since electrochemical reactions rely on variations of the electrochemical potential, the need for a different reference arises, as in traditional OECT-based systems the source electrode operates not only as a modulated channel extremity, but also as reference. Therefore, we evaluate the actuating ability of the OECT by monitoring the drain potential against a Saturated Calomel Electrode (SCE). Vd and Ed variations were registered respectively with a sourcemeter and a potentiostat, providing a correlation with dopamine concentration. The final comparison between the two parameters report a significative enhancement in Ed modulation, while presenting also different values. In the final procedure, the device successfully responds to dopamine additions with controlled Ed variations, that can be further employed to achieve electrochemical actuation. Thus, the previous results were exploited to induce a dopamine-driven electrochromic actuation of a ITO electrode covered by Prussian Blue (PB), connecting the drain electrode to the electrochromic PB actuator. Dopamine electrochemical oxidation triggers a potential variation across all circuit elements, resulting in PB reduction to Prussian White, as evidenced by the visual color change from blue to transparent. The system described is the first step towards analog intelligent systems, that allow both sensing and actuation in a single device.3 References 1 E. K. Boahen, H. Kweon, H. Oh, J. H. Kim, H. Lim, D. H. Kim, Bio-Inspired Neuromorphic Sensory Systems from Intelligent Perception to Nervetronics. Adv. Sci. 2025, 12, 2409568. 2 Gualandi, I., Tonelli, D., Mariani, F. et al. Selective detection of dopamine with an all PEDOT:PSS Organic Electrochemical Transistor. Sci Rep 6, 35419 (2016). 3 D’Altri, G., Mariani, F., Bonafè, F., Decataldo, F., et al., in preparation.