A biosensor made of photosynthetic complexes from plants

Photosynthetic reactions in plants, algae, and cyanobacteria are driven by photosystem protein complexes, which exchange electrons with partner biomolecules. Photosynthetic complexes can also bind synthetic organic molecules, which mediates their photoactivity and enables sensing of herbicides and algicides, or the study of electron transport chains. Thus, development, characterization, and sensing of photosystem complexes bears both fundamental and applied interest. Binding to the plastoquinone sites of photosystem-I provides a promising route to biosensing, and would enable identifying novel substances displaying phytotoxic effects, including those obtained from natural product extracts. To this end, we have devised a procedure to attach photo- and redoxactive photosystem I complexes to the surface of transparent gold, and we obtained reproducible electrochemical photo-responses with direct current readout. Using this novel biosensing platform, we measured photocurrents in the presence of the viologen derivative paraquat at concentrations as low as 100 nM, with a biosensor dynamic range spanning six orders of magnitude up to 100 mM concentration.