Abstract: Technology described in this document can be embodied in a system for detecting analytes in a biochemical sample. The system includes a container configured to contain the biochemical sample. The system also includes a light source, an optical detector, a lens, and an optical aperture. The lens is disposed between the container and the optical detector, and the optical aperture is disposed between the lens and the optical detector. The system further includes a structure configured to house the container, the optical aperture, the lens, and the optical detector.