Uncrosslinked Thermoresponsive Hybrid Magnetic Nanospheres Directly Prepared from Poly(N-isopropylacrylamide) that Behave as Heating Rate Nanosensors

Poly(N-isopropylacrylamide) (PNIPAM) provides thermoresponsiveness to nanoobjects containing magnetic/plasmonic nanoparticles (NPs) for biosensing and biomedicine. Conjugation methods include the grafting of PNIPAM onto NPs or the embedding of NPs in PNIPAM nanogels. Nanoobjects are often obtained simultaneously with monomer (NIPAM) polymerization, and the cytotoxicity of unreacted NIPAM represents a non-negligible concern. Herein, a facile and versatile miniemulsion method employing already polymerized PNIPAM is developed. Miniemulsion is achieved through PNIPAM globulization above the lower critical solution temperature (LCST) and stabilized by poly(vinyl alcohol) (PVA). Aqueous decants, obtained after solvent evaporation, contain thermoresponsive nanospheres with PNIPAM/PVA blends, stable in water for months, monomodal in size at high magnetic NP contents, biocompatible and with hyperthermia capability. Unlike the shrinking/swelling displayed by PNIPAM-based nanogels, these uncrosslinked nanospheres disintegrate/rebuild, with a size after disintegration undoubtedly related to their heating rate across LCST, behaving as unprecedented dual hyperthermia agents and heating rate nanosensors without further sensing molecules.