The invention relates to imparting photoreactivity to target cells, e.g., retinal cells, by introducing photoresponsive functional abiotic nanosystems (FANs), nanometer-scale semiconductor/metal or semiconductor/semiconductor hetero-junctions that in this case include a photovoltaic effect. The invention further provides methods of making and using FANs, where the hetero-junctions bear surface functionalization that localizes them in cell membranes. Illumination of these hetero-junctions incorporated in cell membranes generates photovoltages that depolarize the membranes, such as those of nerve cells, in which FANs photogenerate action potentials. Incorporating FANs into the cells of a retina with damaged photoreceptor cells reintroduces photoresponsiveness to the retina, so that light creates action potentials that the brain interprets as sight.