Fabrication of reversible phase transition polymer gels toward metal ion sensing

We report the synthesis of a new type of triple stimuli-responsive, i.e., thermo-, pH-, and metal ion-responsive copolymers based on poly(N- vinylimidazole-co-methacrylic acid) (poly(VI-co-MAA)) and their application as metal ion sensors. The copolymers exhibit reversible sol-gel phase transition behavior in aqueous media. The sol-to-gel transition temperature (T _sol-gel) can be shifted in the range of 20-80 °C, by varying monomer ratio and feeding glycerol content, by adjusting the copolymer concentration in aqueous solution, by tuning the pH of the solution, or by adding various divalent metal ions. Metal ion sensors were designed upon an inverse opal photonic film loaded with aqueous solution of poly(VI-co-MAA), which allows the easy reorganization of various divalent metal ions by combining the diversity of T_sol-gel of the copolymers on different metal ions and flexible reflection spectra of the film. In addition, a fluorescent reversible sol-gel transition system was established by in situ generation of nanocrystals in the copolymer matrix. These extensions may provide the multiresponsive copolymers great flexibility for applications in biomedical, optical, and sensory fields.