Ratiometric Fluorescence Probe Based On Gold Nanoclusters And Carbon Dots And Study On Heavy Metal Multivariate Detection

Gold nanoclusters（Au NCs）and carbon dots（CDs）are considered as the most promising fluorescent nanomaterials in the field of chemical sensing due to their excellent optical properties,low toxicity,high stability and fluorescence tunability.Firstly,this work investigated the synthesis,properties,sensing mechanism and application of Au NCs and CDs.Considering that single-emission probes are easily influenced by the concentration of probe,instrument efficiency,test conditions and other factors,the ratiometric fluorescence probes with pleasurable detection precision was constructed for the simultaneous detection and recognition of multiple heavy metal ions in environmental water samples based on the unique fluorescence properties and specific recognition ability of Au NCs and CDs to realize multivariate detection.This work not only creates the detection of a variety of analytes,a precedent for the synchronization of detection and removal for heavy metal pollution,but also provides a novel idea for the design of AIE fluorescent probes.The novel gold nanoclusters（NG-Au NCs）stabilized by N-acetyl-L-cysteine（NAC）and glutathione（GSH）with aggregation-induced emission（AIE）characteristic and intrinsic the peroxidase mimic activity was designed and synthesized.The NG-Au NCs showed strong orange emission with quantum yield（QY）of 10.6%,microsecond fluorescence lifetime（7.53μs）and high component of Au（I）species（61.36%）.It was worth noting that NG-Au NCs can not only act as fluorescent probe for sensing Hg²⁺and Ag⁺by“turn off”and“turn on”mode with with limit of detection（LOD）0.87 n M and47.0 n M,but also serve as a peroxidase-like to participate in the construction of NG-Au NCs-H₂O₂-TMB colorimetric system to accomplish the successive detection of H₂O₂and GSH concentration with the LODs of 2.9μM and 0.22μM,respectively.The sensing mechanism of Hg²⁺and Ag⁺detection by NG-Au NCs was analyzed systematically.which confirmed that the“turn off”and“turn on”fluorescence responses are caused by the reversible variation of AIE phenomenon.In addition,as a multiple fluorescence-colorimetric dual-mode probe,NG-Au NCs also showed great potential for the detection of multiple analytes in environmental water and actual blood samples.The bifunctional magnetic carbon dots（M-CDs）were synthesized via systematic structure manipulation,which was applied for fluorescence detection and continuous magnetism removal of Hg²⁺.The M-CDs exhibited an intense blue emission with QY of55%.Based on the internal filter effect and static quenching effect,the M-CDs can be served as a fluorescent probe to detect Hg²⁺sensitively and rapidly from the tap water and yellow sea with a low LOD of 5.40 n M.Moreover,the M-CDs exhibited paramagnetism with a saturation magnetization of 22.70 emu/g.By virtue of commendable selectivity for Hg²⁺and its intrinsic paramagnetism,the detection and magnetic removal of Hg²⁺were synchronously realized,and the removal efficiency was up to 98.30%.More importantly,the removal behavior of Hg²⁺by M-CDs can be repeated at least three turns,indicating that M-CDs can accurately detect and remove Hg²⁺from water samples.The ratiometric fluorescent probe（Au NCs@CDs）fabricated by NG-Au NCs and M-CDs was constructed and employed as probe for heavy metals detection.Based on AIE effect,the multivariate probes were constructed.The Au NCs@CDs probe showed a single emission peak at 452 nm when the excitation wavelength was 367 nm,which can achieve selective detection of Ag⁺in real water samples.Under the same conditions,the addition of Ag⁺leaded to the appearance and enhancement of emission peak at 610nm with LOD of 3.17 n M.Based on this,Au NCs@CDs probe was improved to construct a novel ratiometric fluorescent probe（Ag⁺-Au NCs@CDs）was developed to employ for the sensitive determination and identification of Hg²⁺and Cu²⁺in practical water sample analysis by dual-responses-OFF mode with LODs of 0.17μM and 0.41μM,respectively.The Au NCs@CDs and Ag⁺-Au NCs@CDs as ratiometric fluorescent sensors offered a new idea for the identification for multiple heavy metal ions.