Implementation of force differentiation in the immunoassay.

A technique has been developed to apply force to the antibody-antigen complex in a solid-phase immunoassay. Force was applied to the immunochemical complex by labeling the secondary antibody with a magnetically susceptible, micrometer-size particle and placing the assay chamber in a magnetic field of defined magnitude and orientation. The force was strong enough to displace weakly bound particles but was not strong enough to rupture the immunochemical complex. The number of particles bound to the surface after applying the differentiation force was related to the analyte concentration, thus an optical detection scheme was developed for counting the number of particles on the surface. The sensitivity of the force differentiation assay was demonstrated to be one to two orders of magnitude higher than conventional solid-phase immunoassay techniques for model protein, virus, and bacterial analytes, with 99% specificity. The enhanced sensitivity of this assay appears to result from lowering the assay background through the identification of weakly adhesive, nonspecific interactions. Copyright 2000 Academic Press.