Fig. 1.

Principle of electrical differential counting of CD4+ T cells. (a) Graphically-rendered image depicting the chip’s geometry, specifically its two electrical counters and capture chamber. Cross-sectional views of the chip during an experiment: (b) forward flow direction to obtain total leukocyte count at the entrance counter, (c) reverse flow direction and enumeration of uncaptured cells after leukocytes reach the exit sensor, and (d) finished experiment after all unbound leukocytes are washed from the capture chamber. The concentration of CD4+ cells can be obtained simply by normalizing the differential count by the known sample volume ((d), right panel). The right panels of (b) and (c) illustrate how cell flow direction at the entrance counter can be determined by the change in pulse signature polarity, with the pulse signature changing from up-down (b) to down-up (c) in time.