Microfluidic approaches to immunoassays

An immunoassay format is presented that takes advantage of the microfluidic properties of the H-Filter(TM) for measuring sample analyte concentration. The method relies on the diffusion of analyte particles into a region containing beads coated with specific antibody. Competitive binding of labeled analyte and sample analyte with a limited number of binding sites allows measurement of the concentration of sample analyte based on the fraction of labeled analyte bound. The fraction of labeled analyte bound can be determined with a microcytometer by measuring the bead fluorescence intensity on the microcytometer portion of an integrated microfluidic chip. It is not necessary to separate the beads from the mixture because the bead intensity can be determined above the background of unbound labeled antigens. Other advantages include the ability to eliminate large interfering particles from samples, continuous sample monitoring and the ability to concentrate the beads. Microfluidic immunoassay formats also consume smaller volumes of costly reagents and sample.