The enhanced diffusional mixing for latex immunoagglutination assay in a microfluidic device

Latex immunoagglutination assay in a microfluidic device is expected to be even easier than its large-sized, commercialized counterpart. However, such demonstration has had a limited success due to the difficulties in mixing in a microfluidic device, especially for the microparticles used in latex immunoagglutination assay. The primary goal of this work is to improve diffusional mixing towards the successful latex immunoagglutination in a microfluidic devices without any non-specific binding. To this end, SDS (sodium dodecyl sulfate, an ionic surfactant) or Tween 80 (polyethylene sorbitol ester, a non-ionic surfactant) was added to the antibody-conjugated polystyrene (PS) microparticle suspension. These surfactant-added particle suspensions were mixed with the target antigen solution at the Y-junction of a microfluidic device. The immunoagglutination and the diffusion behavior were visually identified with an inverted light microscope. Both surfactants showed some problems such as non-specific binding (with SDS) or very poor diffusion (with Tween 80). As an alternative approach, therefore, highly carboxylated PS microparticles, where the surface is saturated with carboxyl-terminated side chains, were evaluated without using any surfactants. These particles showed very low non-specific binding comparable to that with Tween 80 and good diffusional mixing equivalent to that with SDS.