Electrical stimulation of retinal ganglion cells with diamond and the development of an all diamond retinal prosthesis

Electronic retinal implants for the blind are already a market reality. A world wide effort is underway to find the technology that offers the best combination of performance and safety for potential patients. Our approach is to construct an epi-retinally targeted device entirely encapsulated in diamond to maximise longevity and biocompatibility. The stimulating array of our device comprises a monolith of electrically insulating diamond with thousands of hermetic, microscale nitrogen doped ultra-nanocrystalline diamond (N-UNCD) feedthroughs. Here we seek to establish whether the conducting diamond feedthroughs of the array can be used as stimulating electrodes without further modification with a more traditional neural stimulation material. Efficacious stimulation of retinal ganglion cells was established using single N-UNCD microelectrodes in contact with perfused, explanted, rat retina. Evoked rat retinal ganglion cell action potentials were recorded by patch clamp recording from single ganglion cells, adjacent to the N-UNCD stimulating electrode. Separately, excellent electrochemical stability of N-UNCD was established by prolonged pulsing in phosphate buffered saline at increasing charge density up to the measured charge injection limit for the material.