Preparation Of Thiol-stabilized Fluorescent Metal Nanoclusters And The Application In Ions And Small Molecule Detection

Sulfhydryl group（-SH）is a negative monovalent functional group composed of a sulfur atom and a hydrogen atom,and also called a thiol group or a hydrogen sulfide group.Sulfhydryl groups are widely present in small molecule compounds and easily interact with gold/silver to form S-Au（Ag）.Therefore,small molecules containing sulfhydryl groups can be used as templates for preparing fluorescent metal nanoclusters（MNCs）,for example,D-Penicillamine（DPA）and glutathione（GSH）.In this paper,based on the interaction between DPA and GSH,DPA@AgNCs,DPA@Ag/CuNCs,GSH@AgNCs and Ag@Ag/CuNCs were prepared,and DPA@Ag/CuNCs was used as a probe to construct fluorescent sensors for detecting Ag⁺and folic acid（FA）in aqueous solutions;Ag@Ag/CuNCs was used as a probe to construct a S^2-sensor based on headspace single droplet microextraction technology.This work focused on the preparation of fluorescent metal nanoclusters and the construction of ions and small molecule sensors in aqueous solutions.The main research contents are summarized as follows:Chapter 1:In this chapter,metal nanoclusters,silver nanoclusters（AgNCs）,and thiol-stabilized AgNCs were described.Silver,as the cheapest precious metal,has catalytic,non-toxic,antibacterial and other properties,and AgNCs have become a research hotspot in the field of natural sciences today.Moreover,studies have shown that thiol-stabilized AgNCs are more attractive in the research field.Compared with macromolecules,thiol-stabilized AgNCs not only have a smaller size,but also have the advantages of high stability,high quantum yield（QY）and easy-functionalization.In addition,the structure and function of small molecules containing sulfhydryl groups,as well as the preparation and applications of thiol-stabilized metal nanoclusters were summarized.Chapter 2:This chapter uses DPA as a template to prepare metal nanoclusters Firstly,using DPA as a stabilizer and Ag NO₃ as raw material,DPA@AgNCs emitting red fluorescence were prepared in a water-soluble preparation solution by a one-pot method.A yellow-emitting DPA@Ag/CuNCs was prepared by doping Cu²⁺,and its QY was increased by fourfold.The experiment explored the optimal conditions for the preparation of metal nanoclusters,and fluorescenceand Uv-visible absorption spectrum（Uv-vis）analysis were carried out,showing that after adding Cu²⁺,the Energy gap（Eg）between HOMO and LUMO in the nanoclusters increased,and the improved Eg enhanced the emission intensity and led to blue shift of the spectrum.The characterization of DPA@AgNCs and DPA@Ag/CuNCs from Flourier-transform infrared（FT-IR）proved that the successful preparation of nanoclusters was attributed to the formation of S-Ag.The scanning electron microscope（SEM）,high resolution transmission electron microscope（HRTEM）and other characterizations showed that the luminescence mechanism of the two was AIEE.Chapter 3:A sensor using DPA@Ag/CuNCs as fluorescent probe for Ag⁺detection was constructed.In the water environment,this experiment found that Ag⁺can aggregate small nanoclusters to form larger nanoparticles,which leads to the quenching of the fluorescence of DPA@Ag/CuNCs.In addition,the sensor had high sensitivity and selectivity.The linear response range of the sensor was 0.05～800μM,and the limit of detection（LOD）was 30 n M.In addition,most common inorganic ions do not interfere with Ag⁺detection.In this experiment,the sensor was further applied to the detection of Ag⁺in real water samples such as tap water,domestic sewage and lake water based on the standard addition method,and the results were satisfactory.Chapter 4:A sensor for detecting folic acid（FA）in medicines was constructed with DPA@Ag/CuNCs as a fluorescent probe.Under certain experimental conditions,FA can significantly quench the fluorescence of DPA@Ag/CuNCs,and the linear response range of the sensor was 0.01～1200μM,the LOD was 5.70 n M.At the same time,under the experimental conditions,most of the common coexisting ions,carbohydrates and amino acids were not affect the experimental results.The quenching mechanism of the sensor was explored in detail with fluorescence spectra,Uv-vis absorption spectra and fluorescence lifetime before and after the reaction.And the results showed that electron transfer quenching was the ultimate cause of fluorescence quenching.The experiment was further based on the standard addition method to apply the sensor to the determination of FA in real samples such as folic acid tablets and infant chewable tablets.The test results were satisfactory,indicating that the detection system can be well applied to the detection of FA in real samples.Chapter 5:GSH@AgNCs with strong blue fluorescence emission were prepared using GSH as template.Subsequently,dual-emitting Ag@Ag/CuNCs were prepared by mixing GSH@AgNCs and DPA@Ag/CuNCs.The experiment further optimized the preparation conditions of composite metal nanoclusters,At the same time,the experiment explored the microstructure of composite metal nanoclusters by using spectral analysis,SEM and HRTEM,and so on.Further experiments found that S^2-can quench the fluorescence of Ag@Ag/CuNCs under certain conditions,Therefoe,a S^2-sensor was constructed with dual-emission metal nanoclusters as probe based on the headspace single-drop microextraction technology.The linear response range of the sensor was 0.01～300μM,and the LOD was 6 n M.At the same time,the S^2-sensor had high selectivity,and most inorganic ions and twenty amino acids had little interference to S^2-detection.The sensing mechanism was discussed,and the addition of S^2-led to aggregation of small Ag@Ag/CuNCs,and formed larger-sized nanoparticles,which eventually resulted in fluorescence quenching.The experiment was further based on standard addition method,the sensor was applied to the detection of S^2-in real water samples（tap water,domestic sewage,lake water）and sludge,and the test results were satisfactory.