Light-addressable electrode with hydrogenated amorphous silicon and low-conductive passivation layer for stimulation of cultured neurons

The authors propose a light-addressable planar electrode with a simple three-layer laminated structure that can induce pinpoint neuronal activation on the culture substrate. The structure consists of a tin oxide $\left(\mathrm{Sn}{\mathrm{O}}_2\right)$ , hydrogenated amorphous silicon $(a\text{-}\mathrm{Si}:\mathrm{H})$ , and passivation layer. The passivation layer was a spin-coated low-conductive zinc antimonate $\left(\mathrm{Zn}\mathrm{O}{\mathrm{Sb}}_2{\mathrm{O}}_5\right)$ -dispersed epoxy, which was proved to be effective for preventing penetration of culture medium and thus avoiding deterioration of $a\text{-}\mathrm{Si}:\mathrm{H}$ layer. Illumination to the electrode locally elevated the conductivity with 60-fold stimulus charge density. The fluo-4 calcium imaging of neurons cultured on the developed electrode showed that the neuronal activation was confined around the illuminated location, thus demonstrating the light-addressing capability of the proposed electrode.