Rapid immunosensing based on accumulation of microparticles by negative dielectrophoresis

In the work, microfluidic device consisting of an interdigitated microarray (IDA) electrode was developed for a rapid, and separation-free immuno-sensors based on a manipulation technique of microparticles by dielectrophoresis (DEP). A poly-dimethylsiloxane (PDMS) substrate with microfluidic channel was placed on the IDA plate to allow to fabricating the device. On applying AC voltage to the IDA in a negative DEP (n-DEP) frequency region, goat anti-mouse immunoglobulin (anti-mouse IgG)-immobilized microparticles moved to the surface of PDMS substrate placed above the IDA by n-DEP force to accumulate at the designated areas of the PDMS surface, where anti-mouse IgG was precoated. When the fluorescence microparticles bearing anti-mouse IgG were suspended in an analyte (mouse IgG) solution, the microparticles trapped the analyte to form microparticle-conjugates. The conjugates were accumulated and captured at the designated areas of the PDMS surface via antibody-antigen-antibody (sandwich) reaction. The captured microparticles were detected selectively by fluorescence measurements at the focused, designated areas regardless of the presence of uncaptured microparticles in the suspended solution. Thus, the separation and washing-out steps, usually required for conventional immunoassay, are eliminated in the presented procedure. Since the formation of the sandwich structures was accelerated significantly by n-DEP, as short as 30 sec was enough to detect the immunoreaction at the surface. The fluorescence intensity of the captured microparticles at the designated area increased with the analyte in the range, 0.01 ~ 10 ng/mL. The present procedure realizes a rapid, sensitive and separation-free immunoassay in a simple device.