Synthesis,Properties And Application Of Fluorescent Metal Copper And Silver Nanoclusters

Metal nanocluster（MNCs）is a kind of molecular aggregate with ultra-small sizes（about 2 nm）,which is composed of several or dozens of hundreds of metal atoms.The core of MNCs is coated with ligand molecules to maintain its stability.Due to its ultra-small sizes,the original continuous metal energy band is split,so it has molecular-like properties.Fluorescence property,as its most unique property,has been widely studied,and many applications of metal nanoclusters are based on it.Herein,we designed and synthesized three different fluorescent metal nanoclusters,and explored their microstructures and fluorescence properties.The specific research contents are as follows:（1）Using glutamic acid（Glu）as a protective ligand,Copper Chloride（CuCl₂）as a metal precursor and ascorbic acid（AA）as a reducing agent,we prepared a stable Glu-protected CuNCs with green fluorescence.The average particle size is about 1.6 nm,the fluorescence excitation and emission wavelengths are 350 nm and 440 nm,respectively.The fluorescence quantum yield is 1.58%and the fluorescence lifetime is 2.19 ns.The fluorescent probe based on Glu-protected CuNCs can be performed in the range of 0-8μM,and the detection limit is as low as 0.048μM.Glu-protected CuNCs fluorescent probe was used to test tap water samples.Fe³⁺was detected by standard addition method.It was found that it has high recovery and low relative standard deviation,indicating that the Glu-protected CuNCs fluorescent probe has certain practical application value.（2）Azobenzene-1-mercapto-2-carboxylic acid（Azo-SH）was prepared and used as a ligand.Azo-SH-protected AgNCs were prepared then by ultrasonic reduction method with silver nitrate（AgNO₃）as a metal precursor.The micro morphology of Azo-SH-protected AgNCs was observed by SEM.It was found that its morphologies could change from small spheres to ultra-long nanofibers during the regulation process from alkaline/neutral to acidic.This process of morphology transition was confirmed to be driven by hydrogen bonding andπ-πstacking.The p H-adjustment process is accompanied by appearance of strong red fluorescence.Based on its fluorescence on/off characteristic in the process of p H regulation,it can be applied to erasable imaging equipment,which has a good imaging on/off effect in practical operation.The azobenzene ligand can change from trans structure to cis structure in a very short time under UV irradiation.After continuous irradiation with visible light for a certain time,it can return to trans structure.In this process,it is accompanied by the aggregation of AgNCs.（3）A lipoic acid-modified poly（vinyl alcohol）macromolecule（PVA-LA）was prepared by esterification of poly（vinyl alcohol）.Using it as a ligand,silver nitrate（AgNO₃）as a metal precursor and sodium borohydride（Na BH₄）as a reducing agent,PVA-LA-protected AgNCs with red fluorescence was prepared.The maximum fluorescence excitation wavelength is 430 nm,the maximum emission wavelength is 640 nm,the Stokes shift is 210 nm,and a shoulder peak is observed at 695 nm.The fluorescent probe for Cu²⁺detection based on PVA-LA-protected AgNCs can be performed in the range of 0-28μM,and the detection limit is as low as 0.71μM.We applied PVA-LA-protected AgNCs to the imaging of mouse ovarian cancer cells（ID8）.The results show that it has low biological toxicity and good imaging effect.