A device includes a lower reservoir surface, an upper reservoir surface, and a reservoir sidewall extending between the upper and lower reservoir surfaces which together define a reservoir. The reservoir is configured to be completely filled by a liquid such that the liquid forms a column contacting the upper reservoir surface, the lower reservoir surface, and the reservoir sidewall, with a meniscus of the liquid being outside of the reservoir. At least one of the upper reservoir surface and the lower reservoir surface is configured to transmit light.