Dual-Responsive Ionically Assembled Fluorescent Nanoparticles from Copoly(Ionic Liquid) for Temperature Sensor

Abstract

A simple copolymer, copoly­(ionic liquid), consisting of <i>N</i>-isopropylacrylamide (NIPAM) and 1-benzyl-4-vinylpyridine bromide (4-VPBn⁺Br^–) units as thermo-responsive and ionic liquid parts, respectively, has been synthesized. Fluorescent nanoparticles (FNPs) were then formed under the driving forces of electrostatic interaction between 2-(4-amino-2-hydroxyphenyl) benzothiazole derivative (AHBTA) and copoly­(ionic liquid) due to hydrophilic/hydrophobic balance. The fluorescent intensity of the FNPs enhanced by a factor of about 50 times when the pH was increased from 7 to 10, and was effectively doubled within 1 °C around LCST in pH 9 buffer solution, thus showing a dramatic pH and thermal dual-dependent property. The FNPs exhibited reversible fluorescence enhancement/quenching over more than five cycles, regardless of the heating/cooling process. Furthermore, the FNPS proved to be much more stable to UV light irradiation than pure fluorescence molecule AHBTA