Human retina can achieve single-photon sensitivity through specialised photoreceptors that convert light into electrical signals via phototransduction. Among microbial light-sensitive proteins, proteorhodopsins stand out for their intrinsic light-driven ion transport and spectral tunability, making them promising candidates for bio-inspired photonic devices. A central challenge for acellular integration, however, is the fragility of most bacterial rhodopsins under extreme conditions. Here, we exploit the exceptional robustness of TARA76, a microbial rhodopsin that retains structural integrity even upon complete dehydration, to demonstrate its functional reconstitution in an artificial black lipid membrane within a biocompatible microfluidic platform. By recording light-induced ionic currents with picoampere sensitivity across a broad range of pH, illumination power, electrolyte composition, and applied voltages, we establish TARA76 as a high-performance photoelectric transducer in a fully acellular environment. Strikingly, we uncover a strong and previously unreported dependence of the photocurrent on Na ions, which appears to play a key structural and functional role in stabilising the protein's active conformation. Furthermore, we demonstrate that the orientation of TARA76 within the artificial membrane can be externally controlled by applying a defined electric field during bilayer formation, enabling deterministic tuning of photocurrent directionality. Together, these results establish a robust and miniaturisable bio-photonic platform with direct implications for quantum light sensing, neuromorphic bioelectronics, and next-generation artificial retinal interfaces.
Cardace, I., Dominici, L., Ardizzone, V., Cola, A., Fieramosca, A., Nobile, C., Polticelli, F., Bruni, F., De Giorgi, M., Ballarini, D., Gigli, G., De Marco, L., Sanvitto, D.
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