We describe a sheath-less micro-cytometer that measures four different parameters, namely fluorescence, large angle side-scatter and dual frequency electrical impedance (electrical volume and opacity). The cytometer was benchmarked using both size and fluorescent bead standards and demonstrates excellent size accuracy (CVs <= 2.1%), sensitivity and dynamic range (3.5 orders of magnitude) at sample flow rates of 80 mu L per minute. The cytometer was evaluated by analysing human blood, and a four part differential leukocyte assay for accurate CD4+ T-cell enumeration was demonstrated. The integration of impedance, fluorescence and side scatter into a single miniature cytometer platform provides the core information content of a classical cytometer in a highly compact, simple, portable and low cost format.
