Electrokinetically driven microfluidic chips with surface-modified chambers for heterogeneous immunoassays

This article presents the first example of a microfluidic chip for heteroge neous bioassays using a locally immobilized biospecific layer and operated electrokinetically. The reaction chamber has picoliter dimensions and is in tegrated into a network of microchannels etched in glass. The high affinity of protein A (PA) for rabbit immunoglobulin G (rIgG) was exploited for chi p testing, with PA being immobilized on microchannel walls and fluorescentl y labeled (Cy5) rIgG sewing as sample. It was possible to operate the chip in an immunoaffinity chromatographic manner, using electrokinetically pumpe d solutions. Concentration of antibody from dilute solution onto the solid phase was demonstrated, with signal gains of similar to 30 possible. A dose -response curve for Cy5-rIgG was obtained for concentrations down to 50 nM, for an incubation time of 200 s. The flexibility of chip layout was demons trated for competitive immunoassay of rIgG using both a combined sample/tra cer incubation and sequential addition of these solutions, With assay times generally below 5 min for this unoptimized device, the microfluidic approa ch described shows great potential for many high-throughput screening appli cations,