Ovarian cancer cells, SKOV3, have been immobilized onto platinum microelectrodes using anti-EPCAM capture antibodies and detected with high sensitivity using electrochemical impedance. The change in impedance following cell capture is strongly dependent on the supporting electrolyte concentration. By controlling the concentration of Dulbecco's phosphate buffered saline (DPBS) electrolyte, the double layer thickness can be manipulated so that the interfacial electric field interacts with the bound cells, rather than simply decaying across the antibody capture layer. Significantly, the impedance changes markedly upon cell capture over the frequency range from 3 Hz to 90 kHz. For example, using an alternating-current (ac) amplitude of 25 mV, a frequency of 81.3 kHz, and an open circuit potential (OCP) as the direct-current (dc) voltage, a detection limit of 4 captured cells was achieved. Assuming an average cell radius of 5 μm, the linear dynamic range is from 4 captured cells to 650 ± 2 captured cells, which is approximately equivalent to fractional coverages from 0.1% to 29%. An equivalent circuit that models the impedance response of the cell capture is discussed. © 2013 American Chemical Society.