On-chip latex agglutination immunoassay readout by electrochemical impedance spectroscopy.

We describe a new class of impedance-based lab-on-chip immunosensors in which the immunoagglutination of latex is monitored by electrochemical impedance spectroscopy (EIS). Antibody-coated latex microspheres agglutinated in the presence of target antigens are precipitated from solution between interdigitated microsized electrodes on a chip. Impedance spectra are reproducibly measured in the 0.1-1 MHz frequency range within several minutes and are shown to be dependent on the aggregate morphology and the sedimentation rates of the agglutinated particles. An equivalent circuit model of the system suggests that the impedance is governed primarily by the electric double layer interactions close to the electrode surface. The effects of sedimentation time, particle type, particle size, and concentration are characterized. The readout method holds promise for developing sensitive miniaturized sensors for rapid immunotesting.