Magnetic Nanoparticles with Thermoresponsive Polymeric Shells for Biomedical Applications

Magnetic iron oxide (Fe₃O₄) nanoparticles are being developed for technological and biomedical applications with great success. One recent example is the use of iron oxide nanoparticles coupled with high frequency oscillating magnetic fields for the treatment of cancer tumors. With the objective of visualizing the temperature distribution inside a cell monlayer in vitro, we are coupling magnetite nanoparticles with a thermoresponsive fluorescent polymer, which effectively acts as a nanothermometer. Magnetite nanoparticles are synthesized and functionalized with poly(N-isopropylacrylamide) (pNIPAM). pNIPAM undergoes a phase transition in water at ~32°C, its Lower Critical Solution Temperature (LCST), changing from a hydrophilic state below this temperature to a hydrophobic state above it. pNIPAM is considered to be appropriate for biomedical applications given the fact that its LCST, is close to body temperature (37°C) and it can be modified by copolymerization with other acrylamide polymers in order to increase it above and below 37°C. A fluorescent monomer (FM) was synthesized and conjugated to the magnetic nanoparticles surfaces. The fluorescence intensity of the FM increases with increasing temperature, after PNIPAM reaches its LCST. AIBN is used as an initiator for free radical polymerization on the particles. X-ray diffraction, Fourier Transform Infrared (FTIR), Dynamic Light Scattering (DLS), fluorescence intensity, and magnetic measurements using a Quantum Design MPMS X17 SQUID magnetometer have been performed on the nanoparticles in order to characterize their physical and magnetic properties.