Multifunctional Magnetic–Fluorescent Nanoparticle: Fabrication, Bioimaging, and Potential Antibacterial Applications

Magnetic–fluorescent nanoparticles integrating imaging and therapeutic capabilities have unparalleled advantages in the biomedical applications. Apart from the dual ability of unique biomolecular fluorescent recognition and magnetic modes, the nanoparticle also endows combined effective therapies with high physiological stability, long-term imaging, rapid response time, and excellent circulation ability. Herein, we developed a carboxyl-functionalized magnetic nanoparticle that was further functionalized by polydopamine (PDA) and Schiff base ligand (3-aminopyridine-2-carboxaldehyde N(4)-methylthiosemicarbazone, HL) to form multilayered coating single nanoparticles (Fe₃O₄@PDA@HL). Our work showed that the aggregation-induced emission (AIE) effect could be produced by embedding In³⁺ into the Fe₃O₄@PDA@HL nanostructure, which offered a new opportunity for utilization as a fluorescent detection and therapeutic platform. Cellular fluorescent imaging experiments provided bacterial cell biodistribution, demonstrating their excellent luminescent performance, magnetic aggregation, and separation capability. We simultaneously confirmed that the synergistic antibacterial effect was closely related to both Fe₃O₄@PDA@HL and In³⁺, leading to the disruption of membrane integrity and the leakage of intracellular components, thus inducing bacterial death. This approach presented in our work could promote the development of future bioimaging and clinical therapy applications.