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

## TL;DR

Researchers created magnetic nanospheres from a temperature-sensitive polymer that can both generate heat and sense heating rates, useful for biomedical applications.

## Contribution

A new method to create biocompatible, thermoresponsive nanospheres without polymerizing monomers in situ, enabling dual hyperthermia and heating rate sensing.

## Key findings

- Nanospheres made from pre-polymerized PNIPAM are stable, biocompatible, and contain high magnetic nanoparticle content.
- The nanospheres disintegrate and rebuild in response to temperature changes, correlating their size with heating rate across LCST.
- They function as hyperthermia agents and heating rate nanosensors without additional sensing molecules.

## Abstract

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.