Role of Clustering Dynamics in Magnetic Nanoparticle-Based Agglutination Sensors

Core–shell magnetic nanoparticle (MNP)-based sensors have enabled homogeneous (wash-free) biosensing owing to their distinctive behavior during colloidal agglutination mediated by surface chemistry. Although MNPs have shown extensive utility in biomolecule labeling and separation, understanding the dynamics of MNP agglutination will further assist their optimization for biosensing applications, particularly for producing concentration-dependent sensor responses. In this study, we establish a design framework for MNP-based agglutination sensors that transduce magnetic relaxation into assay readouts. Carboxymethylated dextran-coated MNPs functionalized with biotin are incubated with streptavidin, and MNP cluster formation upon reaction is characterized using alternating current magnetization and dynamic light scattering. Our results reveal that receptor density is an effective control for manipulating the analyte-response region. Further, statistical analyses indicate that a logistic relation captures the essential behavior between analyte concentration and the resulting MNP agglutinate size. Importantly, this study connects nanoscale surface functionalization to agglutination-driven signal generation, providing practical guidance for engineering magnetic nanomaterials for applied sensing with enhanced sensitivity.