Extracellular Electron Transfer from Photosynthetic Microalgae Modulates the Response of Electrolyte-Gated Organic Transistors

Abstract Photobioelectrochemical systems exploit photosynthetic organisms to convert solar energy into electrical energy, thus enabling emerging applications in sustainable energy harvesting, biosensing, and bioelectronics. Here, we integrate living microalgae within a biohybrid electrolyte-gated organic transistor (EGOT) to create a photoresponsive device that is modulated by the metabolites of microalgae photosynthesis. The biohybrid gate electrode is fabricated on indium tin oxide (ITO) by drop-casting a microalgae cells suspension mixed with a PEDOT:PSS water dispersion. Upon illumination, the microalgae initiate the photosynthetic electron transport, driving extracellular electron transfer toward the ITO electrode, thus leading to the direct coupling of photosynthetic activity and modulation of transistor current. The resulting process is a light-induced electron flow at the gate that modulates the charge carrier density in the organic semiconductor channel through the faradaic gating mechanism. The light-driven gating response depends on functional photosynthetic electron transport at the biohybrid gate and can be implemented in both depletion- and accumulation-mode EGOTs. Notably, the response arises from faradaic processes at the gate–biofilm interface and not from the direct photo-modulation of the channel material. This is a clear demonstration of how intercepting metabolic pathways of a living system may provide sustainable energy conversion for driving low-power electronic devices.