Concentrated Polymer Brush-Modified Magnetic Particles for a Diagnostic Immunoassay

Nonspecific protein absorption is an ongoing problem in the development of highly sensitive magnetic particle (MP)-based diagnostic assays, whereby the MP surface undergoes biofouling, significantly reducing the limit of detection and sensitivity of the device. In this study, a bioinert, concentrated polymer brush (CPB) composed of poly[poly(ethylene oxide) methyl ether methacrylate] (PPEGMA) was employed to reduce the absorption of protein onto the MP surfaces; and an anti-human serum albumin antibody (Ab) was then immobilized onto the brush layer by click chemistry to demonstrate its application as an immunoassay platform. The amount of antibody grafted onto the ends of the brush coating was quantified by a BCA assay with a high grafting efficiency (∼0.80 antibody per chain). Furthermore, when using the antibody-conjugated CPB-coated MPs (MP-PPEGMA-Ab) as an immunoassay platform, we were able to determine the capture efficacy of human serum albumin (HSA) in both a buffered solution and diluted human serum by colorimetric analysis, and further confirmation was achieved via liquid chromatography/mass spectrometry, in which our MPs showed a high selectivity toward the targeted analyte. Lastly, we demonstrated that MP-PPEGMA-Ab was capable of detecting human serum albumin at a concentration as low as 6.4 ng mL⁻¹, 30% more sensitive than the unmodified MP, demonstrating the impact of CPBs on diagnostic assays. Due to their high selectivity and sensitivity, our CPB-based MPs are expected to be applicable for a wide range of immunoassay applications by employing different bioinert polymers and biofunctional groups.