The photochemical core of every photosynthetic apparatus is the reaction center, a transmembrane enzyme that converts photons into charge-separated states across the biological membrane with an almost unitary quantum yield. We present a light-driven organic transistor architecture, which converts light into electrical current by exploiting the efficiency of this biological machinery. Proper surface tailoring enables the integration of the bacterial reaction center as photoactive element in organic transistors, allowing the transduction of its photogenerated voltage into photomodulation of the output current up to two orders of magnitude. The device architecture, termed Light-driven Electrolyte-Gated Organic Transistor (LEGOT), is the prototype of a new generation of low-power hybrid bio-optoelectronic organic devices. Main text Evolution has engineered multi-protein complexes to efficiently convert solar radiation into chemical energy, [1] sustaining the energy needs of life on planet Earth via the photosynthetic process. These photoenzymes catalyze the uphill conversion of oxidized molecules to their reduced forms, using light as energy source. Photosynthetic organisms, such as plants, algae, and some bacteria are the sole kind of organisms on the planet able to harvest and store energy. [2] The photosynthetic anoxygenic bacteria possess a photosynthetic apparatus based on a single functional unit, the reaction center (RC), which converts photons into charge-separated states across the membrane with unmatched quantum yield. Rhodobacter (R.) sphaeroides is a purple non-sulphur bacterium, whose RC is a three-subunit transmembrane protein sitting within the photosynthetic membrane. [3] Light impinges a cascade of electron transfer reactions that forms the hole-electron couple with a unitary quantum yield. [4] In absence of exogenous electron donors and acceptors, this state does not evolve further and has a lifetime ranging from hundred milliseconds up to three seconds. [5] See Figure S1 in the Supporting Information.

The photosynthetic reaction center (RC) from the Rhodobacter sphaeroides bacterium has been covalently bioconjugated with a NIR-emitting fluorophore (AE800) whose synthesis was specifically tailored to act as artificial antenna harvesting light in the entire visible region. AE800 has a broad absorption spectrum with peaks centered in the absorption gaps of the RC and its emission overlaps the most intense RC absorption bands, ensuring a consistent increase of the protein optical cross section. The covalent hybrid AE800-RC is stable and fully functional. The energy collected by the artificial antenna is transferred to the protein via FRET mechanism, and the hybrid system outperforms by a noteworthy 30% the overall photochemical activity of the native protein under the entire range of visible light. This improvement in the optical characteristic of the photoenzyme demonstrates the effectiveness of the bioconjugation approach as a suitable route to new biohybrid materials for energy conversion, photocatalysis, and biosensing.

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