An immunoassay in which magnetic beads act both as collectors and sensitive amplifiers for detecting antigens in a microfluidic chip (MFC)–quartz crystal microbalance (QCM) system

An immunoassay based on the enrichment of antibodies by magnetic beads (MB) and their subsequent detection of antigens in a microfluidic chip (MFC)–quartz crystal microbalance (QCM) was developed and investigated. The MB conjugated to goat anti-human-immunoglobulin G (MB-anti-h-IgG) were concentrated within microchannels by the application of a magnetic field, which also functioned as a separation switch outside the MFC. The conjugation of the MB and the anti-h-IgG antibody in the MFC was completed in 1 min. Removal of the magnetic field allowed the resulting tributary buffer solution to flush the MB-anti-h-IgG out of the MFC and onto a QCM chip. The combination of the MB-anti-h-IgG and the QCM chip amplified the detection sensitivity of antigen(s) to 10−1 ng/ml. By controlling the enrichment velocity and sample injection mode in the MFC, a linear response ranging from 10−1 to 103 ng/ml was obtained. This technique establishes a simple, rapid MFC method for the amplification of a QCM-based immunoassay.