ZnFe2O4 Magnetic Nanoparticle–Polydiacetylene–Zinc(II) Composites for Real-Time Nanothermometers and Localizable Acid/Base Sensors

Nanocomposites of polydiacetylene (PDA) and magnetic nanoparticles (MNPs), exhibiting irreversible thermochromism, have shown potential for use as nanothermometers. This type of nanocomposite, however, does not allow measurement of the real-time temperature. In this study, we introduce the first example of magnetic PDA-based nanocomposites, exhibiting reversible thermochromism and colorimetric response to both acidic and basic conditions. Zinc ferrite magnetic nanoparticles (ZnFe2O4-MNPs) decorated the surface of PDA/Zn2+ assemblies, forming PDA/Zn2+/ZnFe2O4 magnetic nanocomposites. The intercalation of Zn2+ ions, released from ZnFe2O4-MNPs, with PDA bilayers via strong interaction with a carboxylate headgroup provides reversible thermochromism. This reversible thermochromic nanocomposite with magnetic properties is ideally suited for advanced applications requiring precise local thermal or pH sensing. For instance, the magnetothermally induced thermochromism of PDA could be implemented for real-time measurement of the local temperature (e.g., magnetic hyperthermia), visualization of the magnetic field, and many other related applications. In addition, the colorimetric response of this material to acids and bases makes possible measurement of the local pH in a small-scale environment, localized at a target area, focused using an external magnetic field.