Solar energy is a highly exploitable energy source for renewable energy technologies; thus, a great deal of recent research has focused on the ability to generate electrical energy from solar energy (photoelectrochemistry). This has resulted in a wide variety of photoactive biomaterials being studied at electrode surfaces, such as isolated photosystems, thylakoid membranes as well intact photosynthetic organisms.

Chloroplasts are photosynthetic organelles that harness solar energy in higher plants and algae. They are the vital sources of carbon-based fuels and have self-repair mechanisms against photo-damage; however, chloroplasts are less studied for harnessing solar energy. The electrochemical communication of chloroplasts at electrode surfaces is challenging since they are shielded inside thick electrochemically-insulating cell membranes. Therefore, the majority of studies surrounding chloroplasts in photobioelectrochemical systems (PBESs) utilize soluble exogenous electron transfer (ET) mediators. The use of soluble electron mediators, however, is not feasible for large-scale application.

Redox polymers are polymeric backbones that have been modified with redox-active moieties and can be used as an immobilization matrix as well as a non-diffusive electron mediator for extracellular-ET from biomaterials to the electrode. Nevertheless, a successful electrochemical study on chloroplasts with any redox polymer is yet to be reported. Here, we report the photoelectrochemical wiring of chloroplasts on a naphthoquinone-based redox polymer. Intact chloroplasts were immobilized on Toray carbon paper electrodes and illuminated under a fiber optic light to simulate sunlight. Cyclic voltammetric and amperometric experiments demonstrate the ability to obtain photo-excited electrons that are produced from water oxidation by intact chloroplasts. In the presence of a diffusive mediator as well as the redox polymer, maximum photobiocurrents obtained from the chloroplasts are as high as 28±5 µA cm^-2.