Plasmon-Enhanced\nPhotoelectrochemistry of Photosystem\nII on a Hierarchical Tin Oxide Electrode for Ultrasensitive Detection\nof 17β-Estradiol

Despite its excellent efficiency in natural photosynthesis,\nthe\nutilization of photosystem II (PSII)-based artificial photoelectrochemical\n(PEC) systems for analytical purposes is hindered due to the low enzyme\nloading density and ineffective electron transfer (ET) processes.\nHere, we present a straightforward and effective approach to prepare\na PSII-based biohybrid photoanode with remarkable photoresponse, enabled\nby the use of a hierarchically structured inverse-opal tin oxide (IO-SnO<sub>2</sub>) electrode combined with gold nanoparticles (Au NPs). The\nporous, carbon-containing IO-SnO<sub>2</sub> structure allows for\na high density and photoactivity loading of PSII complexes, while\nalso providing strong electrical coupling between the protein film\nand the electrode. A new electron transfer pathway mediated by Au\nNPs was identified at the protein-electrode interface, which efficiently\nshuttles the photogenerated electrons from the enzyme to the IO-SnO<sub>2</sub> electrode. Furthermore, the PEC response of the electrode\nwas significantly enhanced by the surface plasmon resonance (SPR)\neffect of Au NPs. Upon light irradiation, this PSII-based photoanode\nexhibited an impressively high and stable photocurrent output, which\nwas utilized to fabricate an aptasensor for 17β-Estradiol (E2)\ndetection. Under optimal conditions, a detection limit of 0.33 pM\nwas obtained, along with a broad detection range from 15 pM to 30\nnM. The applicability of the aptasensor was assessed by measuring\nE2 in water and urine samples, demonstrating its feasibility in environmental\nmonitoring and clinical tests.