| Magnetite nanoparticles are attractive for biomedical applications such as magnetic fluid hyperthermia (MFH), a novel cancer treatment, due to their ability to induce heating through energy dissipation in an oscillating magnetic field. This application requires suitable nanoparticle surface modification which provides colloidal stability in biological fluids and improves the nanoparticle’s transport and retention in specific areas of the human body. We studied the synthesis of multifunctional magnetic nanoparticles coated with silane-functional molecules, which allow the expression of amine or acrylate end groups on the nanoparticle surface. These functional end groups were used to graft attractive materials such as carboxy-methyl dextran (CMDx) or a thermo-responsible polymer such as poly(N-isopropyl acrylamide) (NIPAM). Highly stable suspensions of CMDx coated magnetic nanoparticles were obtained over a broad range of pH and ionic strength. The effect of these nanoparticles on viability of human colon (CaCo-2) and mammary (MCF-7) cancer cells was study in vitro, as well as the distribution/transport of particles in these cells. The energy dissipation of CMDx coated magnetic nanoparticles was determined upon the application of an oscillating magnetic field at 233 kHz and 6.6 kA/m. Surface modification of magnetic nanoparticles with a fluorescent thermo-responsive polymer such as poly(NIPAM-co-FMA) can be used to visualize temperature profiles during MFH application. Furthermore, we present an approach to using AC susceptibility measurements in studying changes in the state of a colloidal suspension, from which we demonstrate how temperature-dependent measurements of the AC susceptibility of a sample at fixed field frequency can be used to identify and interpret transitions in suspensions of magnetic nanoparticles coated with thermo-responsive polymers. |
