Molecular photovoltaic structures for optical activation of excitable cells: current advances and perspectives

Current neural stimulation devices for the treatment of sensory and motor disorders are based on electrical stimulation. Using this technique, neural activity is triggered by electrical stimuli applied through electrodes in contact with the cells. Due to physical constraints of the electrodes the spatial control of stimulation is limited, which in some cases generates unwanted side effects. In addition, adverse tissue reactions occur after long term contact with the electrodes. A potential solution is the application of methods based on light instead of electrical energy, in which the electrical stimulator and the electrode are replaced by a light source and an optical fiber. Although optical stimulation approaches that allow spatially selective, highly specific and contact-free control of the neural activity have been developed in recent years, their implementation requires genetic manipulation, limiting the perspectives for clinical applications. A molecular photovoltaic structure potentially able to mediate light-induced cellular responses without involving genetic modification is the photosynthetic pigment-protein complex Photosystem I (PSI). In this work, the recent advances on the application of PSI reaction centers for optical control of cellular activity are presented. Perspectives of application of PSI reaction centers in the development of future methods for clinical neural stimulation are also presented.