A means for orienting flat cells in flow systems

Flattened cells, such as red blood cells, epithelial cells, and sperm of many species, cause problems for fluorescence-activated cell analysis and sorting machines because the flow systems of such devices are unable to control the orientation of these cells as they flow past the detectors. For this reason, the fluorescence or scattered light measurements for identical cells may vary greatly. A flow geometry is here described that orients flat cells in a coaxial flow system so that each cell presents the same aspect to the observation device. A wedge-shaped exit on the sample injection tube in a coaxial flow system is sufficient to produce the desired orientation effect when used with low sample flow rates. Data is presented showing the effect of orientation of fixed chicken erythrocytes on histograms of small forward-angle light-scattering measurements.