Preparation And Sensing Applications Of Fluorescent Copper Nanoclusters-based Materials With Enhanced Emission

Copper nanoclusters（CuNCs）with molecular-like properties cause widespread concern because of its unique optoelectronic properties.In particular,photoluminescence is one of the most extensive properties of the CuNCs.However,due to the easy oxidation nature of Cu element,most CuNCs show low quantum yield,poor chemical stability,and difficulty in the size control,which greatly limit their application.Aiming at a series of problems existing in the synthesis method,optical property regulation and fluorescence sensing application of CuNCs,the following research works were carried out in this paper.In chapter 2,by using polyethyleneimine as template,copper nanoclusters（PEI-CuNCs）were prepared with a simple UV-light-induced approach and used for the detection biothiols,and acetylcholinesterase（ACh E）.Cu²⁺can rapidly quench the fluorescence of PEI-CuNCs.Biothiols with-SH functional groups can react with Cu²⁺to form the RSH–Cu²⁺complex,making Cu²⁺-triggered fluorescence quenching turned on.ACh E can hydrolyze acetylthiocholine into thiocholine（TCh）,which reacted with Cu²⁺to form TCh–Cu²⁺complex and turned on Cu²⁺-quenched fluorescence.A typical inhibitor of ACh E,tacrine,was also detected by this convenient fluorescence turn-off-on assay.Besides,this assay was successfully used for sensing biothiols and ACh E activity in human serum samples.Results proved that the enormous prospect of PEI-CuNCs and open up a new path for questing their extensive biosensing applications.In chapter 3,an electrostatically controlled fluorescence assay based on silver/copper bimetallic nanoclusters integrated with graphene oxide was developed.Polyethyleneimine-protected silver/copper bimetallic nanoclusters（PEI-Ag/CuNCs）with positive charges were firstly synthesized with interesting p H/temperature-dependent to quench the fluorescence of PEI-Ag/CuNCs by inner filter effect（IFE）.Based on different electrostatic interactions,three kinds of biomolecules,negatively charged heparin,positively charged protamine,and trypsin were recognized.This strategy provided a new approach for wider applications of electrostatically controlled fluorescence assay for sensing biomolecules.In chapter 4,the surface confinement effect of CuNCs based on 2D layered double hydroxide（LDH）was proposed to prepare the fluorescence composites of glutathione protected CuNCs and LDH（GSH-CuNCs/LDH）with excellent quantum yield and long fluorescence lifetime.Moreover,a novel,simple,and ultrasensitive fluorescence assay for the detection of hyaluronidase was proposed based on the surface confinement effect.For the first time,this work developed a bio-enzyme sensing platform based on the surface confinement effect,which can serve as promising candidates in biosensing.In chapter 5,Zn-containing hydroxy double salt（Zn-HDS）was synthesized and employed as the host material,which exhibits advantages of both large surface area and high charge density.Confinement induced enhanced emission based on Zn-HDS as host material and glutathione-protected copper nanoclusters（GSH-CuNCs）as guest molecules was firstly developed to form the fluorescence composite,GSH-CuNCs/Zn-HDS.Compared with GSH-CuNCs,the prepared GSH-CuNCs/Zn-HDS showed higher quantum yield,longer fluorescence lifetime,and better stability.Based on the inner-filter effect,GSH-CuNCs/Zn-HDS was applied to construct a bio-enzyme sensing platform for the sensitive and visible detection ofβ-glucuronidase.Moreover,a stable,low-cost,and environmentally friendly light-emitting diode was fabricated by the solid-state powder of GSH-CuNCs/Zn-HDS.In chapter 6,a fast,convenient,and low-cost method of detecting water was developed based on a ratiometric fluorescence probe composed of fluorescent Cu nanoclusters（CuNCs）and carbon dots（CDs）.CuNCs with solvent-dependent effects have different responses to water in various solvents while CDs are ideal fluorescence reference because of their excellent fluorescence stability.With the increase of water content in organic solvents,the ratiometric fluorescence probe exhibited an obvious color change from orange to blue and was employed for the sensitive detection of water contents via fluorescence intensity ratios（orange/blue）.Smartphone as a portable tool was introduced to quantitatively analyze the visual results by acquire images,read colors,and analyze data.Moreover,the developed water sensing platform was applied to the detection of water contents in white wine and medical alcohol samples,proving its great potential in practical applications.