Biological semiconductors: self-assembled shell proteins as photoactive materials

Light-harvesting proteins are promising biocompatible materials for bioelectronics, yet their instability and inefficient charge transport hinder direct integration. External scaffolds offer support but introduce energy losses and delay response. Here, we identified a class of hyper-thermostable, self-assembling bacterial shell proteins that form disc-like structures with spatially organized tyrosine residues, facilitating efficient light absorption and charge transport. <i>I</i>-<i>V</i> profiling and ultraviolet photoelectron spectroscopy reveal their semiconducting behavior and low work function (<3 eV). These protein discs generate photocurrents under UV illumination without external bias and achieve external quantum efficiencies (∼0.5%) and response times (0.3 s) surpassing those of traditional photosynthetic proteins by an order of magnitude. Mutational analysis implicates a tyrosine-mediated electron transfer mechanism. These findings establish bacterial shell proteins as intrinsically stable, scaffold-free photoactive materials for next-generation bioelectronic applications.