A fluidic structure includes a channel, a portion of which can contain fluid. Light can propagate in the portion, such as in response to illumination. The refractive index of material at the portion's boundary can be higher than that of the fluid, and more than approximately 10% of intensity of light propagating longitudinally occurs in the fluid, possibly approximately 90%. An IC can be positioned along the portion, with a set of cells of a photosensor array on the IC sensing photons emanating in response to the propagating light. The light can enter through a light-transmissive component along the channel's boundary, then pass obliquely through a portion of the channel that contains air before passing through a bounding component and obliquely into the portion that can contain fluid. The light can couple to an anti-resonant waveguide mode.