Nanosieving for rapid, solution‐phase immunoassays

Abstract

We demonstrate an innovative nanosieving technique for rapid solution-phase measurement of antibodies. Polyacrylamide membranes were fabricated by in situ UV lithography in glass microchannels. Membrane pore-size was optimized to exclude large species, while small proteins (<10 kDa) electrophoretically migrate through the membrane. For detection of unlabeled antibodies, buffer containing anti-insulin IgG was electrophoretically loaded into the microchannel. Owing to the large size of IgG, the antibody was retained at the membrane interface. A known concentration of FITC-labeled insulin (Ins*) was introduced. Retention of Ins* at the membrane indicated formation of Ins*-IgG complexes (see figure), as unbound Ins* migrates through the membrane when IgG is not present. Fluorescence signal at the membrane enabled IgG quantitation. The device exploits advantages of scale-dependent transport processes in confined geometries, namely for rapid immunorecognition. Unlike protein microarrays, no surface immobilization is necessary. The reported assay could allow study of previously unusable binding pairs and binding kinetics. Funding from UC Berkeley is gratefully acknowledged.