An optical analysis box for a flow cytometry system that includes: a plurality of connected walls defining a volume; a connection interface associated with at least one of the walls and configured to connect with an imaging device; a sample receiver configured to hold a fluid sample in the volume; and an analysis region having an aperture configured to align with an imaging element of a connected imaging device, the analysis region being positioned such that gravity forces flow of the held fluid sample past the aperture for imaging by the imaging device.