Constraints on the channel dimensions include whether a spore can enter and move through a channel smoothly, and how challenging and repeatable the fabrication would be. For example, a narrow microchannel will suffer from blockage during sensing and a too small gap between Au electrodes may risk short-circuiting. Finite element computation showed that to obtain a significant change (>5%) in the DC resistance (Rsol) the inter-electrode gap needed to be no more than three times and the channel height and width no more than four times the zoospore diameter (Supporting Information, Figure ). As an example, Figure ) shows the result of finiteelement computation of the current flow at 50 kHz and impedance |Z| between the electrodes for the final device design, with a model zoospore passing across the 10 m gap between electrodes disposed on the base of a channel 20 um high and 20 um wide.