Microfluidic synthesis and accurate immobilization of low-density QD-encoded magnetic microbeads for multiplex immunoassay†

Magnetic-fluorescent microbeads have been widely used in the multiplex detection of biological molecules. The traditional method relies on flow cytometry to decode and analyze the microbeads. Alternative strategies that employ immobilized microbeads on a plane and involve fluorescence imaging to analyze the microbeads have been proposed. Among these strategies, an integrated chip that controls magnetic field contribution using nickel powder pillars and captured microbeads has attracted great attention. Despite its unique advantages such as low manufacturing costs, reusability and high capture efficiency, existing research had been limited by the inability to precisely capture a single microbead, and the overlapping of microbeads has made multiplex immunoassays based on this strategy impossible. In this work, low-density microbeads were prepared in a microfluidic chip using IBOMA as the main monomer. The low density of the microbeads made the preparation of an aqueous suspension easier. An integration of nickel patterns, magnets and channels was carried out and demonstrated the capacity of capturing single microbeads precisely. Fluorescence coding further empowered this method with the ability of multiplex immunoassay, which was verified using three types of IgG, and a calibration curve for the detection of anti-human IgG was established using a sandwich immunoassay. These results show the promising potential of this strategy for biomedical detection.