and increases again above the focal plane fig3 c and 6 show this process in more detail the cross section of the flow tube that can be conveniently imaged is not dependent on the opacity of the sample fluid and can be very large say a square of dimension 3 mm u00d7 3 mm allowing an extremely high flow throughput of sample it is expected that flow throughputs of greater than 1 ml minute can be achieved in a straightforward way it is expected that the flow velocity will be low enough to be laminar because of slower flow of particles near the walls of the tube particles near the walls may appear in multiple images and this effect preferably is taken into account when calibrating the device calibration can be effected by using samples of calibrated fluorescent beads of uniform intensity this invention when combined with the use of fluorescent antibodies to selectively tag microorganisms allows the detection of pathogenic microorganisms in food and water just to name two applications for example e coli o157 h7 is detected in a buffer solution extracted from ground beef high resolution images allow determination of the size of the fluorescently tagged particles allowing for screening based on size determination it is.