Fig. 3.

Experimental setup and process for electrical differential counting of CD4+ T cells. A dual lock-in amplifier is used to inject an AC signal and monitor its change through the chip’s counter regions, which are balanced by a Wheatstone configuration. Process: (1) the cells pump injects leukocytes into the chip (forward direction) to be enumerated at the entrance counter; (2) after cells are sensed at the exit counter, both valves are switched to reverse flow direction and the PBS wash pump purges the capture chamber of uncaptured cells, which are enumerated again by the entrance counter.