Construction And Application Research Of Fluorescent Probe Based On Copper Nanoclusters

The fluorescent metal nanoclusters have wide application prospects in biological analysis and environmental analysis due to their advantages of simple synthesis,unique optical properties and good biocompatibility.Compared with precious metal nanoclusters such as gold and silver,the copper nanoclusters?Cu NCs?are cheap.However,the Cu NCs are prone to agglomeration and their bare surface is easily oxidized by air,resulting in poor stability.Many red glowing Cu NCs have weak fluorescence performance and low quantum yield,which is not conducive to further analysis and application.In this paper,the following studies were carried out on the stability of red luminescent Cu NCs,the regulation of fluorescence performance and the sensitivity of the analysis and detection of the target in biological samples.The specific content is divided into the following three parts:Part 1:Glutathione?GSH?plays key roles in biological systems,it is critically valuable to construct highly sensitive and accurate sensors for its quantification in studying the oxidative stress reaction and related diseases.Here,we reported the synthesis of aggregation-induced emission?AIE?-Cu NCs prepared through Cu?II?reduction by using L-cysteine?Cys?as both the reducing and capping agents.The Cys-Cu NCs displayed AIE properties and large stokes shift?235 nm?.The fluorescence of Cys-Cu NCs is quenched by MnO₂ nanosheets through inner filter effect.Upon introduction of GSH,the MnO₂nanosheets were reduced to Mn²⁺and the quenched fluorescence of Cu NCs was recovered.On this basis,an ultrasensitive nanosensor was developed for GSH with the detection limit of 1.2 nM,which is at least 5-fold lower than previous FL sensors based on MnO2.The fluorescent sensing strategy was successfully applied for GSH detection in human serum samples with good accuracy and high reproducibility,suggesting the potential applicability of this system for analysis of GSH in practical biological samples,disease monitoring and clinical diagnosis.Part 2:To further improve the fluorescent properties of Cu NCs,biocompatible polydopamine?PDA?templating strategy is introduced for the in-situ synthesis of AIE type Cu NCs.The resulting PDA coated Cu NCs?PDA-Cu NCs?exhibit 28-fold higher of quantum yield than that of sole Cu NCs.They show orange emission at 580 nm when excitation at 340 nm.The Stokes shift between photoluminescence excitation and emission is large,over 240 nm.Benefiting from PDA,their storage stability is greatly improved to at least two weeks.Intriguingly,the fluorescence of PDA-Cu NCs is quenched by Fe³⁺ion but is recovered by PO₄^3-due to its stronger affinity for Fe³⁺.The nanoprobe shows ultrasensitive response to PO₄^3-in the range of 0.003 to 70.0?M with determination limit?LOD?of 1.5 nM.Noticeably,compared with Cu NCs,PDA-Cu NCs displays 25-fold increase in sensitivity for PO₄^3-.The PDA-Cu NCs-based FL nanoprobe was also successfully applied to determining the for PO₄^3-in real water samples.Based on this,PDA-Cu NCs are able to be used as ion-driven fluorescence?FL?switch for sensing of phosphate.In the presence of ACP,PO₄^3-is produced by the catalytic hydrolysis of ATP?ACP substrate?.The limit for ACP activity measurement is 0.001 U.L^-11 and a linear ACP activity curve is observed over the range of0.0012-25 U.L^-1.Part 3:We used kojic acid?KA?as reducing and capping agents synthesize the green luminescent Cu NCs and non-fluorescent Cu-MOF by hydrothermal method in one pot.Unconventional AIE-type KA-Cu NCs modified by non-thiol compounds with good photostability,storage stability and high fluorescence quantum yield?17.6%?were prepared.Surface confinement induced enhanced emission?CIEE?effect based on Cu-MOF as host material and KA-Cu NCs as guest molecules was developed to improve the fluorescence intensity,stability and fluorescence quantum yield of Cu NCs.Moreover,Cu2+induced AIE phenomenon in Cu NCs,which also enhanced the fluorescence of Cu NCs and regulated the fluorescence properties of Cu NCs.Hence,a simple“turn-on”fluorescent probe was constructed to detect Cu²⁺.The nanoprobe shows sensitive response to Cu²⁺in the range of0.01 to 80.0?M with determination limit?LOD?of 3.3 nM,and it was successfully applied to the determination of Cu2+in human serum and tap water samples.Therefore,this work not only successfully synthesized new AIE-Cu NCs,but also realized the luminescence regulation of Cu NCs and sensitive Cu²⁺detection,which makes Cu NCs have greater potential in practical applications.