Photopatterning proteins and cells in aqueous environment using TiO₂ photocatalysis

Organic contaminants adsorbed on the surface of titanium dioxide (TiO₂) can be decomposed by photocatalysis under ultraviolet (UV) light. Here we describe a novel protocol employing the TiO₂ photocatalysis to locally alter cell affinity of the substrate surface. For this experiment, a thin TiO₂ film was sputter-coated on a glass coverslip, and the TiO₂ surface was subsequently modified with an organosilane monolayer derived from octadecyltrichlorosilane (OTS), which inhibits cell adhesion. The sample was immersed in a cell culture medium, and focused UV light was irradiated to an octagonal region. When a neuronal cell line PC12 cells were plated on the sample, cells adhered only on the UV-irradiated area. We further show that this surface modification can also be performed in situ, i.e., even when cells are growing on the substrate. Proper modification of the surface required an extracellular matrix protein collagen to be present in the medium at the time of UV irradiation. The technique presented here can potentially be employed in patterning multiple cell types for constructing coculture systems or to arbitrarily manipulate cells under culture.