Microfluidic-based multiplex immunoassay system integrated with an array of QD-encoded microbeads

Here, we developed a multiplex immunoassay platform within microfluidic devices that combines suspension and the planar microarray format. For the suspension microarray format, QD-embedded polymeric microbeads with an average diameter of 24 μm were prepared using the Shirasu Porous Glass (SPG) membrane emulsification technique. To furnish the microbeads with resolvable spectral codes, QDs with two different colors (450 nm for blue and 520 nm for green) were used and different spectral codes were obtained by changing the ratio of emission intensity of the two different QDs within the microbeads. The surfaces of the QD-encoded microbeads were then functionalized with probe antibodies for immunoassays. The planar microarray format was achieved by an array of microholes fabricated in PDMS. Each microhole was designed to trap a single microbead and eventually generated a microbeads array within the microfluidic system. The feasibility of the microbead array within microfluidic devices for use in a multiplex immunoassay was demonstrated by immunobinding assays between IgG and anti-IgG and/or between IgM and anti-IgM. Furthermore, the resultant microbead-based on-chip assay could be used for a sandwich assay to detect prostate-specific antigen (PSA), a model cancer marker, with a detection limit of 1 ng/mL. The combination of suspension and the planar microarray format enabled the spatial location of individual microbeads within physically separated regions and thus facilitated the simultaneous determination of different targets that interacted with the corresponding microbeads.