Tunable Polymer-Brush Interfaces on Magnetic Beads Enable Enhanced Chemiluminescence Immunoassay

The rational design of functionalized colloidal interfaces plays a critical role in chemiluminescence immunoassay (CLIA) performance. However, achieving high antibody loading and efficient signal output through conventional surface modification remains challenging. Herein, a surface-initiated atom transfer radical polymerization (SI-ATRP) strategy is developed to construct Fe₃O₄@PAA core-shell magnetic beads with precisely controlled surface architectures, featuring tunable polymer brush thickness and grafting density (0.05∼0.48 chains/nm²). By systematically varying the initiator loading and monomer feed, a clear structure-property relationship is established between brush architecture, surface carboxyl density, antibody immobilization, and interfacial sensing performance. The optimized beads achieve a 23-fold enhancement in chemiluminescence intensity and increase the signal-to-background ratio from 79 to 575 for creatine kinase MB (CK-MB) detection, with a limit of detection of 0.11 ng/mL. The analytical performance is rigorously evaluated, and the method is validated using 50 clinical plasma samples, demonstrating the robustness of the engineered biointerface for practical diagnostic applications.