A medium having microfluidic circuitry for sampling and analyses. The medium may be a cartridge having a window countersunk into it and containing a flow channel. The flow channel may have items of interest flowing through it. Analyses of these items may be optical involving one or more light sources emanating light to and one or more light detectors receiving light from the channel. There are various configurations so that source and detector light cones may reach the flow channel without obscuration or interference of the light to and from the flow channel in the window.