Microfluidic synthesis of dual-encoded microbeads for multiplex immunoassay

Magnetic-fluorescent microbeads had been extensively used in various applications, particularly in the multiple detection of biological molecules. Currently, most commercially available magnetic-fluorescent microbeads had simple structures and the fluorescence intensity was inversely proportional to the concentration of magnetic particles, which affected performances of microbeads. In this work, a three-dimensional capillary microfluidic system was constructed to produce magnetic-fluorescent core-shell microbeads. Magnetic nanoparticles were dispersed in the core of the microbeads, while the shell consisted of quantum dots (QDs). Core-shell structures restricted fluorescence quenching caused by magnetic nanoparticles in the core area. Moreover, the number of cores could be adjusted precisely, which provided an additional encoding method besides the traditional fluorescence encoding. Three types of dual-encoded core-shell microbeads which exhibited excellent uniformity and fluorescence characteristics with additional magnetic response properties were produced. The self-assembly of silica nanoparticles on the surface of microbeads made the introduction of carboxyl groups easy. Furthermore, the capability of these microbeads for multiplex immunoassays was demonstrated using three types of IgG, and a calibration curve for the detection of human IgG was established using a sandwich immunoassay. These results indicated the potential application of this scheme in the field of biomedical detection.