Enhanced specificity of immunomagnetic separation of bacteria in milk via hydration layer modulation of iron oxide particles.

Efficient capture and separation of target bacteria in complex food matrices remain challenging due to non-specific binding (NSB) of bacteria to the surface of carrier particles. This study investigates the role of surface functionalities in modulating NSB to develop a highly specific, antibody-based magnetic separation system for Salmonella Typhimurium in whole milk. NSB was primarily driven by coordination between exposed surface iron and phosphate groups on bacterial membranes. Comparative analysis of surface-modified iron oxide particles (IOPs) revealed that hydroxyl-rich coatings more effectively suppressed NSB than carboxyl-based modifications, owing to the formation of dense hydration layers. Leveraging these findings, dextrin-functionalized immuno-IOPs were optimized to achieve over 80 % capture efficiency for S. Typhimurium while maintaining minimal NSB, even in the presence of high concentrations of non-target bacteria. This work provides mechanistic insights into antifouling surface engineering and establishes a promising platform for selective bacterial separation in food safety and diagnostic applications.