Rapid quantification of bio-particles based on image visualisation in a dielectrophoretic microfluidic chip

We studied an imaging-based technique for the rapid quantification of bio-particles in a dielectrophoretic (DEP) microfluidic chip. Label-free particles could be successively sorted and trapped in a continuous flow manner under the applied alternating current (AC) conditions. Both 2 and 3 mu m polystyrene beads at a concentration of 1.0 x 10(7) particles ml(-1) could be rapidly quantified within 5 min in our DEP system. Capturing efficiencies higher than 95% could be 2 mu m polystyrene beads with a linear flow speed, applied voltage and frequency of 0.89 mm s(-1), 20 Vp-p and 5 MHz. Yeast cells (Candida glabrata and Candida albicans) could also be captured even at a lower concentration of 2.5 x 10(5) cells ml(-1). Images of aggregative particles taken from the designed trapping area were further processed based on the intensity of relative greyscale followed by correction of the particle numbers. The imaging-based quantification method showed higher agreement than that of the conventional counting chamber method and proved the stability and feasibility of our AC DEP system.