Synthesis And Applications Of Novel Fluorescent Silver Nanoclusters Based On Multi-Chelating Site Polymer Templates

Silver nanoclusters have attracted wide attention due to their unique fluorescence properties,excellent biocompatibility and favorable water solubility.The polymeric templates with multi-chelating points can stabilize silver nanoclusters between polymer chains,prevent their aggregation to control their size and thus improve their solution stability.Meanwhile,the template also largely determines the optical properties of silver nanoclusters.In this work,novel multi-chelate point polymers were used as templates to fabricate controllable fluorescent silver nanoclusters with excellent properties,and their applications in optical detection and biological imaging were also studied.The optical properties of the nanoclusters were studied in detail by using time-resolved fluorescence(TCSPC),UV-Vis absorption spectroscopy,transmission electron microscopy(TEM)and Fourier transform infrared spectroscopy(FT-IR).The effects of solvent type,temperature and p H on the fluorescence properties of nanoclusters were carefully investigated,and the applications of chemical sensing and biological imaging of nanoclusters were further explored.The main research contents are as follows:(1)N-isopropylacrylamide(NIPAM)and acrylic acid(AA)were used as temperature-sensitive and p H-sensitive monomers to synthesize the poly(N-isopropylacrylamide-co-acrylic acid)(P(NIPAM-co-AA)),which was applied as a template to prepare the temperature-sensitive and p H-sensitive silver nanoclusters P(NIPAM-co-AA)-Ag NCs.The fluorescence intensity of the silver nanoclusters showed a good linear and reversible response in the temperature range of 15 to 65°C,and the resolution was up to 0.45°C,which made them suitable for the field of fluorescence nanotemperature detection.At the same time,the silver nanoclusters also exhibited p H-sensitive fluorescence properties,and their linear responses ranged from p H 4.95 to 11.02.In addition,the fluorescence excitation ratio at two specific wavelengths(I_Ex=305nm/I_Ex=453nm)showed a good linear response in the p H range of 5.94-11.02,which could be used to quantitatively detect p H changes.The excellent temperature/p H sensitivity of the nanoclusters made them became ideal tools for multi-responsive sensing and ratio fluorescence detection.(2)The poly(itaconic acid-co-acrylic acid)(P(IA-co-AA))was prepared by using itaconic acid(IA)and acrylic acid(AA)as monomers.The poly(itaconic acid-co-acrylic acid)-templated silver nanoclusters P(IA-co-AA)-Ag NCs were synthesized by photoreduction method.The nanoclusters were stable over a wide range of p H values,and blue emission could be detected at 450 nm under acidic conditions,while orange-red emission could be detected at 600-850 nm under weakly acidic,neutral to alkaline conditions.Additionally,the nanoclusters displayed strong photoluminescence in the second near-infrared region(1050 nm).The aggregation induced emission(AIE)effect was also observed when the ratio of water and ethanol in the solvent was changed.When the volume fraction of ethanol reached 90%,the fluorescence intensity of the clusters increased by eight times compared with that of pure water.The AIE effect was also found in the second near infrared region.The nanoclusters dispersed in 90%ethanol solvent under neutral conditions had very long fluorescence lifetime,which indicated that the photoluminescence of the clusters was actually phosphorescence.Finally,the nanoclusters were successfully used in cell imaging.The nanoclusters showed low toxicity,excellent permeability and high luminescence efficiency,which made them ideal materials for biological imaging.