Visible-Light Neural Stimulation on Graphitic-Carbon Nitride/Graphene Photocatalytic Fibers

Light stimulation allows remote and spatiotemporally accurate operation that has been applied as effective, noninvasive means of therapeutic interventions. Here, visible-light neural stimulation of graphitic carbon nitride (g-C₃N₄), an emerging photocatalyst with visible-light optoelectronic conversion, was for the first time investigated. Specifically, g-C₃N₄ was combined with graphene oxide (GO) in a three-dimensional manner on the surfaces of electrospun polycaprolactone/gelatin (PG) fibers and functioned as a biocompatible interface for visible-light stimulating neuronal differentiation. The enhanced photocatalytic function of g-C₃N₄ was realized by spreading g-C₃N₄ on GO coated electrospun (PG) microfibers to improve both charge separation and surface area. Ascorbic acid (AA) was used in the cell culture medium not only as a photoexcited hole scavenger but also as a mediator of GO reduction to further improve the electrical conductivity. The successful coatings of g-C₃N₄, GO, and AA-mediated GO reduction were confirmed using scanning electron microscopy, photoluminescence, Raman spectroscopy, and X-ray photoelectron spectroscopy. Biocompatibility of g-C₃N₄ (0.01-0.9 mg/mL) to PC12 cells was confirmed by the lactate dehydrogenase (LDH) assay, Live-Dead staining, and colorimetric cell viability assay CCK-8. Under a bidaily, monochromatic light stimulation at a wavelength of 450 nm at 10 mW/cm², a 18.5-fold increase of neurite outgrowth of PC12 was found on g-C₃N₄-coated fibers, while AA-reduced GO-g-C₃N₄ hybrid brought a further 2.6-fold increase, suggesting its great potential as a visible-light neural stimulator that could optically enhance neural growth in a spatiotemporal-specific manner.