After the above validation using the guiding flow, we utilised chemotaxis as the mechanism for selectively extracting zoospores from the flow, as illustrated in Figure . The idea is to have zoospore samples loaded to one side of the channel and attractants loaded to the other side to form a concentration gradient based on diffusion. Two pairs of electrodes as two independent sensing channels (CH1 and CH2) were monitored simultaneously. In this way, the travelling speed of the zoospores, which was controlled by the pumping rate, can be calculated as v= L/t, where v is the velocity of zoospores, L is the distance between the two pairs of electrodes and t is the time difference between CH1 and CH2 when the peak signal appears (Figure ). Impressively, by correlating the signal with the optical videos (Supporting Information, Video 3), high sensitivity and accuracy in zoospore counting was demonstrated despite the high travelling speed of zoospores within the flow (~10 mm/s).