Preparation Of Fluorescent Au/Ag Nanoclusters And Its Application In Food And Drug Detection

In recent decades,significant progress has been made in the research of sensors based on metal nanoclusters（MNCs）for the detection of specific analytes.MNCs are usually composed of several to several hundred metal atoms,and their size is generally less than 2 nm and they have excellent physical and chemical properties.Similar to organic small molecule probes,MNCs can display absorption and emission characteristics by interacting with light to induce electronic transitions between energy levels.Therefore,MNCs are widely used in different fields,such as chemical sensors,biological imaging,catalysis,environment and electronic devices,etc.Single metals based on Au,Ag,Cu and Pt and bimetallic nanoclusters based on Au-Ag,Au-Cu,Au-Pd and Au-Pt as potential fluorescent sensing materials have been applied to the chemical sensingand biosensing of various analytes,including metal ions,anions,biomolecules,proteins,pH of solutions,and nucleic acids.However,its detection applications in food and medicine are less.Therefore,we prepared gold-silver nanoclusters with high fluorescence properties through a simple and green synthesis method,and studied in depth.Based on the specific response of the cluster fluorescence to certain substances in food and medicine,several fluorescence sensors have been constructed.The specific work is carried out from the following aspects:（1）Poly（sodium-p-styrenesulfonate）-enhanced and D-penicillamine stabilized Ag nanoclusters（PSS-DPA-AgNCs）were prepared using one-step ultraviolet irradiation combined with microwave heating method,and the effects of the AgNCs photo-luminescence performance based on different typesofpolyelectrolytes and energy suppliers were studied detailedly.The as-prepared AgNCs can detectiron（II）lactate hydrate（ILH）,ammonium ferric citrate（AFC）,2-Mercapto-3-butanol（2-M-3-B）,3-Mercapto-2-butanone（3-M-2-B）and silicate(SiO₃^2-),respectively.The fluorescence（FL）quenching of PSS-DPA-AgNCs by Fe³⁺（it is obtained from oxidized ILH/ionized AFC）mainly derives from a dynamic quenching process.Excellent linear relationships exist between the FL quenching efficiency（F/F₀）ofthe AgNCs and the concentrations of ILH/AFC in the range of 0.17-6.00/0.067-3.33μmol·L^-1,and corresponding limit of detection（at 3σ/slope）is 12.40/6.04 nmol·L^-1.In addition,the fluorescence（FL）of PSS-DPA-AgNCs is quenched with the addition of2-M-3-B/3-M-2-B/SiO₃^2-mainly originating from a static quenching process.The method can monitor 2-M-3-B/3-M-2-B/SiO₃^2-with a linear response in the range of0.33-90.0/0.33-80.0/3.33-00.0μmol·L^-1and a 74/250/278 nmol·L^-1detection limit（at3σ/slope）.Moreover,the AgNCs probe was extended to the assays of ILH in tablets,solid beverage or ILH additive,AFC in two kinds of edible salts or syrup,two food flavors in the steamed bread and soda drinks and silicate in the mineral water samples with satisfactory results.In addition,the AgNCs probe reveals a good temperature sensing capability.（2）By adding MnO₂nanosheets（MnO₂NS）to regulate the photoluminescence of alloy Au/Ag nanoclusters（NCs）and thiamine（VB1）simultaneously,a simple and novel ratiometric fluorescent probe（RF-probe）was established for sensitively and selectively sensing of proanthocyanidins（PAs）.The introduction of Ag（I）ions can enhance significantly the quantum yields（QYs,11.1%）of Au/AgNCs based on the method of UVI（UV irradiation）combined with MWH（microwave heating）.Impressively,the fluorescence（FL）of Au/AgNCs quenches markedly in the presence of MnO₂NS mainly coming from F（?）rster resonance energy transfer（FRET）,while MnO₂NS as a nanozyme catalyst,can directly catalyze the oxidation of nonfluorescent VB1 to produce highly fluorescent oxVB1 by dissolved oxygen.Upon introduction of PAs as a target,MnO₂NS is reduced to Mn²⁺and lose its quenching capacity and oxidase-like activity,causing that FL of oxVB1 and Au/AgNCs reduces and recovers,respectively.Thus,the RF-probe can monitor PAs with a linear response in the range of 0.27-22.4μmol·L^-1and a 75.9 nmol·L^-1detection limit.Furthermore,the proposed method was extended to the assay of PAs in mineral water,PAs additive and PAs capsule with satisfactory results.（3）A stable,water-soluble,heightened quantum yields（QYs）Au/Ag nanoclusters by the alliance between doping Ag and dual ligands（BSA and thiosalicylic acid）（TSA/BSA-Au/AgNCs）was prepared using a one-step wet chemical synthesis.The effects of different types of aromatic thiols and the molar ratio of Au-Ag on the Au NCs photo-luminescence performance were discussed in detail.The alloy NCs is shown to be viable fluorescent method for vitamin B12（VB12）and chlortetracycline hydrochloride（CCH）assays,and become an excellent temperature sensor in the range of 10-50°C.The fluorescence（FL）of TSA/BSA-Au/AgNCs quenches with the addition of VB12 or CCH coming from FRET combined with inner filter effect（IFE）.The method can detect VB12/CCH by fluorometry with a linear response in the range of 0.33-60.0/0.33-60.0μmol·L^-1and a 71.0/64.0 nmol·L^-1detection limit.Furthermore,the proposed method was extended to the assays of VB12 in mineral water or tablets and CCH in veterinary drug or ointment with satisfactory results.