A Rapid and Sensitive Impedance-Based Immunosensor Utilizing Dielectrophoretic Manipulations of Polyaniline Modified Nanoprobes

In this paper, we have fabricated a simple impedimetric bioanalytical device for the sensitive label free detection of specific immunoreactions. The device consists of a gold interdigitated microelectrode array that utilizes a positive dielectrophoretic (DEP) force to focus and concentrate the nanoprobes (conductive PANI-coated Al₂O₃ nanoparticles conjugated to antibody). A novel surface modification technique has been used to obtain a strongly adhered coating while antibody immobilization occurs via covalent bonding between the amino groups on the PANI surface and the aldehyde groups of the binder, glutaraldehyde. As proof of concept, we have used this immunosensor for detecting the immunoreaction of bovine serum albumin (BSA) with antibovine serum albumin. We have compared the sensitivity of the device at different concentrations of BSA ranging from 1 nM to 1 μM, with and without using DEP. Results show that the impedance change is directly proportional to the concentration of BSA used and can be magnified to about 2-3 times using DEP, thus providing an effective means for immobilization of the nanoprobes and improving the overall sensor sensitivity. Experimental impedance results match well with simulated results obtained using an equivalent circuit model. Thus, this disposable lab-on-a-chip device can be used in clinical settings for the quantitative detection of immunoassays with results obtainable within an hour.