A capillary flow-driven microfluidic system for microparticle-labeled immunoassays.

A simple, reliable, and self-powered capillary flow-driven microfluidic platform is developed for conducting microparticle-labeled immunoassays. To obtain the washing forces and binding kinetics appropriate for microparticle-labeled immunoassays, both microchannel networks and sample access holes are designed and characterized to confirm the fluidic routes. To demonstrate two different types of immunoassays, serial and parallel capillary-driven microfluidic platforms were developed for mouse immunoglobulin G (IgG) and cardiac troponin I (cTnI) using detection antibody-conjugated microparticles, respectively. With the serial capillary-driven microfluidic platform, we successfully demonstrated IgG quantification using direct immunoassay and achieved a limit of detection (LOD) of 30 pM by using pre-immobilized mouse IgG. In the parallel capillary-driven microfluidic platform, a sandwich immunoassay for detecting cTnI was demonstrated and a clinically relevant LOD as low as 4.2 pM was achieved with minimal human intervention. In both assays, the association rate constants (Ka ) were measured to estimate the overall assay time. According to these estimations, microparticle-labeled immunoassays could be conducted in a few minutes using the proposed capillary-driven microfluidic devices. By coupling with various magnetic sensors, these simple immunoassay platforms enable us to achieve a true sample-in-answer-out device that can screen for a variety of targets without relying on external power sources for fluidic manipulation.