Preparation, characterization, and utilization of multi-functional magnetic-fluorescent composites for bio-imaging and magnetic hyperthermia therapy

Abstract

This paper describes the synthesis, characterization, and utilization of unique multi-functional magnetic composites that integrate optical and magnetic properties in a single structure for use in hyperthermia therapy, and magnetic and fluorescence imaging. The composites are comprised of nanoscale magnetic core particles that are encapsulated by a silica layer that contains covalently-embedded organic dyes. The morphologies of the nanocomposite particles were characterized by TEM and FE-SEM. Their optical and magnetic properties were evaluated by spectrofluorometry and SQUID magnetometry, respectively. The results demonstrate that the nanocomposites are monodisperse and uniformly spherical with well-defined shell–core structures; moreover, they exhibit high magnetic saturation, produce vivid fluorescence, and can be designed to provide exceptional stability in aqueous solution over a wide range of pH and at elevated temperatures. For the three dyes utilized in the synthesis of these composites, rhodamine B (RhB), fluorescein (Flu), and 7-hydroxycoumarin (Cou), the observed relative stability for the nanoparticles was: RhB-SiO₂–Fe₃O₄ > Flu-SiO₂–Fe₃O₄ > Cou-SiO₂–Fe₃O₄. Additionally, potential uses of these composite nanoparticles as bimodal contrast agents and therapeutic entities are demonstrated.