Photoelectric Properties of a Light-Addressable Electrode with a Low-Conductive Passivation Layer and Spatial Resolution of the Light-Addressed Electrical Stimulation

Abstract

Conventional microelectrode arrays (MEAs) cannot always access desired neurons due to low electrode density and small electrode number. To overcome this problem, we have proposed and developed a light-addressable planar electrode on a glass substrate. The electrode has a 3-layer structure, namely a transparent SnO2 layer, an hydrogenated amorphous silicon (a-Si:H) layer, and a low-conductive passivation layer. Illumination to the a-Si:H layer increases the conductivity of a-Si:H and generates a virtual electrode at the surface of the illuminated site. In the present study, we evaluated the photoelectric property of the developed electrode and estimated the spatial resolution of the light-addressed stimulation. Illumination to the electrode increased stimulus intensity by up to 60-folds. This illumination-induced intensity change sufficiently followed high-frequency illumination switching. The simultaneous fluo-4 Ca2+-imaging, thus, successfully monitored post-stimulus fluorescence transients by instantaneously shutting out the excitation light during stimulus pulse application. By monitoring stimulus induced responses of cell aggregations, we estimated the spatial resolution of the light-addressed stimulation at 10 μm or more with an addressing illumination spot of 70 μm in diameter.