Construction Of Fluorescent/colorimetric Sensors Based On Silver/Copper Nanomaterials And Their Application In Environmental Detection

In recent years,with the development of nanotechnology,nanomaterials have been attracted extensive attention due to their unique properties.Silver-,copper-containing inorganic nanocomposites have been widely used in the fields of sensing and catalysis.Based on this,silver nanoclusters,copper-carbon dot nanozymes and copper hydrogel nanozymes with excellent performance were prepared in this paper.Fluorescent/colorimetric sensors were constructed using the above materials to realize the sensitive and selective detection of some toxic and harmful substances（Ag⁺,dichlorvos and potassium perfluorooctane sulfonate）in the environment,and were successfully used for the analysis of actual samples.The main contents of this paper are as follows:Chapter 1:This chapter mainly introduces optical sensors,nanomaterials and the application of nanomaterials in optical sensors.The optical sensors mainly introduce the concept and application on colorimetric sensors and fluorescent sensors.In addition,the concept and preparation methods of metal nanoclusters,nanoparticles and nanoenzymes are introduced.Based on the above background analysis,the design ideas of this paper and the background and current situation of the research are described.Chapter 2:Hydrophobic silver nanoclusters were synthesized by chemical reduction using 1,3-phenyldimercaptans and triphenylphosphine as protective agents,and then micellated by N-methylpyrrolidone and sodium acetate to form red phosphorescent silver nanoclusters with a high stoker shift（380 nm）(Ag₂₉@Na micelle).It was found that Ag⁺could quench the phosphorescence of Ag₂₉@Na micelles,and thus a Ag₂₉@Na micelles-based phosphorescence sensor was constructed for sensitive,selective and rapid detection of Ag⁺.The linear range of the sensor was from 1 n M to 100 n M,and the detection limit was 0.8 n M（S/N=3）.In addition,the sensor had good selectivity for Ag⁺.The quenching mechanism of Ag₂₉@Na micelles by Ag⁺was studied in detail by using various analytical and characterization techniques,such as UV-Vis absorption spectrum,photoluminescence lifetime,X-ray photoelectron spectroscopy,transmission electron microscopy and zeta potential.The results showed that the aggregation between Ag₂₉@Na micelles and Ag⁺led to the phosphor quenching.Finally,the Ag₂₉@Na micelles-based phosphorescence probe was applied to detect Ag⁺in lake water samples,and the recoveries were 98%～108%.Chapter 3:Carbon dots（CDs）were prepared by hydrothermal method using sodium tartrate and adenine as precursors,and then copper-carbon dot aerogels（Cu-CDs）with high peroxidase-like activity were constructed based on the reaction and interaction between CDs and copper ion(Cu²⁺).It was found that during the preparation of Cu-CDs,CDs not only reacted with Cu²⁺as reducing agents to form Cu⁺,but also coordinated with Cu²⁺and Cu⁺as complex agents.Studies on the catalytic mechanism of Cu-CDs nanozyme showed that reactive oxygen species such as·OH,·O₂^-and ¹O₂ were produced during the catalytic process of Cu-CDs.These reactive oxygen species can rapidly oxidize o-phenylenediamine（OPD）to produce yellow product 2,3-diaminophenol（DAP）.In the whole catalytic process,the rapid redox cycle of Cu²⁺/Cu⁺,abundant metal-binding sites and three-dimensional porous structure are beneficial for the enhancement of the peroxidase-like activity.Based on this,Cu-CDs were coupled with acetylcholinesterase and choline oxidase to construct a colorimetric sensor based on multi-enzyme cascade catalysis,which realized the sensitive and selective detection of organophosphorus pesticide dichlorvos.The linear range of the sensor was 0.02-0.3μM,and the detection limit was 7.6 n M（S/N=3）.Finally,the sensor was applied for the detection of dichlorvos in cabbage,cabbage and lake water,and the recoveries was 96～106%.Chapter 4:Copper hydrogels were simply synthesized using 6-mercaptopurine and copper nitrate by aqueous heating method.The results showed that the hydrogels acted as peroxidase-like nanozyme,which efficiently catalyzed the oxidation of the substrate 3,3’,5,5’-tetramethylbenzidine（TMB）by H₂O₂ to form an oxidized product,ox TMB.It was found that perfluorooctane sulfonate（PFOS）remarkably inhibited the activity of the nanozyme,and thus a copper hydrogels-based colorimetric sensor was constructed for the detection of PFOS.The linear range for the PFOS sensor was0.025-2μM,and the detection limit was 5.3 n M（S/N=3）.The sensor had the advantages like simple preparation,high sensitivity and good selectivity,and was applied to detect f PFOS in lake water with recoveries of 97%-107%.