title: Responsive polymers-based dual fluorescent chemosensors for Zn2+ ions and temperatures working in purely aqueous media.
abstract: We report on the fabrication of responsive double hydrophilic block copolymers (DHBCs)-based dual fluorescent chemosensors for Zn(2+) ions and temperatures and investigate the effects of thermo-induced micellization and detection conditions on the probing sensitivity and binding reversibility of Zn(2+) ions. A novel quinoline-based polarity-sensitive and Zn(2+)-recognizing fluorescent monomer (ZQMA, 6) was synthesized at first. Well-defined DHBCs bearing quinoline-based Zn(2+)-recognizing moieties (ZQMA) in the thermoresponsive block, PEG-b-P(MEO(2)MA-co-OEGMA-co-ZQMA), were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO(2)MA), oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA), and ZQMA in the presence of PEG-based macroRAFT agent. The OEGMA contents in the thermoresponsive block varied in the range of 0-12.0 mol % to tune their lower critical solution temperatures (LCSTs). At 20 °C, almost nonfluorescent PEG-b-P(MEO(2)MA-co-ZQMA) molecularly dissolved in water and can selectively bind with Zn(2+) ions over other common metal ions, leading to prominent fluorescence enhancement due to the coordination of ZQMA with Zn(2+). At a polymer concentration of 0.2 g/L, the Zn(2+) detection limit can be down to ~3.0 nM. PEG-b-P(MEO(2)MA-co-ZQMA) self-assembles into micelles possessing P(MEO(2)MA-co-ZQMA) cores and well-solvated PEG coronas upon heating to above the LCST, and the fluorescence intensity exhibit ~6.0-fold increase due to the fact that ZQMA moieties are now located in a more hydrophobic microenvironment. Compared to the unimer state at 20 °C, although PEG-b-P(MEO(2)MA-co-ZQMA) micelles possess a slightly decreased detection limit for Zn(2+) (~14 nM), reversible binding between ZQMA moieties and Zn(2+) ions at 37 °C can be achieved, as evidenced by the on/off switching of fluorescence emission via the sequential addition of Zn(2+) and EDTA. In vitro fluorescence imaging studies suggested that the micelles can effectively enter into living cells and sensitively respond to Zn(2+) ions. This work represents the first example of a purely aqueous-based polymeric Zn(2+) sensing system by integrating the well-developed small molecule Zn(2+)-sensing moieties with stimuli-responsive DHBCs.
authors.affiliation: CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Liu
authors.forename: Shiyong
authors.initials: S
authors.lastname: Liu
mesh_terms: D002623:Chemistry Techniques, Analytical / Q000295:instrumentation*; D005456:Fluorescent Dyes / Q000737:chemistry; D006367:HeLa Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D011108:Polymers / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014867:Water / Q000737:chemistry*; D015032:Zinc / Q000032:analysis* / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D008823:Micelles; D011108:Polymers; D014867:Water; D015032:Zinc