Biomolecular electronics: observation of oriented photocurrents by entrapped platinized chloroplasts

Electrical contact of the electron transport chain of photosynthesis has been achieved by precipitating colloidal platinum onto the surface of thylakoid membranes. This composite metal-biological membrane material was immobilized on filter paper and sandwiched between metal gauze electrodes. Upon irradiation, oriented photocurrents were observed. The direction of the flow of photocurrent was consistent with the vectorial model of photosynthesis, which predicts that the electric potential of the external surface of photosynthetic membranes swings negative with respect to the internal surface. Control experiments indicated that the oriented nature of the observed photocurrents could not be attributed to structural asymmetries associated with electrodes or to light gradients associated with the direction of illumination.