Study On Accurate Detection Of Heavy Metals In Food And Medicine By Multiple Quantum Dots Fluorescence Sensor

As an important role in industrial society,heavy metals exist in all aspects of our lives.Due to the characteristics of heavy metals,such as easy migration,high cumulation and persistence,there are safety risks of metal pollution in the environment.In particular,excessive levels of heavy metals are commonly found in food and pharmaceutical raw materials�Chinese medicinal materials,which pose a great threat to human health.Therefore,it is imperative for the national economy and human livelihood to detect the heavy metal content in foods and medicines to prevent excessive levels of heavy metals.Although the traditional heavy metal detection methods are highly sensitive,the applied instruments are expensive,also require the professional operation and consume time and materials,which is not conducive to widespread promotion.At present,the fast detection method of heavy metal detection is commonly used,which solve some problems of traditional detection methods due to its advantages of quickness,simplicity and low cost.However,there still have some problems of susceptibility to interference,low sensitivity and poor selectivity.Therefore,a new rapid detection method for heavy metals is urgently needed,which is fast,simple,low-cost,high precision and high specificity and easy to popularize.The purpose of this thesis is to use a multi-quantum dots fluorescence sensing method to achieve fast,simple and accurate quantification of heavy metal ions in food and medicine.The main research contents are as follows:Chapter 1:IntroductionBegining with an overview of the heavy metal pollution in the environment,especially in food and medicine.Based on the analysis of the existence forms,migration pathways and toxicological mechanisms of heavy metals in the environment,the causes of heavy metal pollution revealed and the serious harm to human health is pointed out.Secondly,six kinds of classical heavy metal detection methods are summarized,the advantages and disadvantages of the classical detection methods are analyzed,and the research hotspots and current research status of heavy metal detection methods are introduced.Based on this,the characteristics and advantages of the detection methods are introduced.Chapter 2:Detection of Lead Ions Based on the"turn-off-on"Mode of ZnCdSeQDsTo solve low sensitivity and poor specificity in the quantum dots detection method for heavy metals,this chapter proposed using Pb²⁺to quench the fluorescence of ZnCdSeQDs.The fluorescence recovery of ZnCdSeQDs could occur since the specifically bind to Pb²⁺by adding S^2-in the detection system,thereby the formed"turn-off-on"detection mode can increase the sensitivity and specificity to Pb²⁺.The detection limit of this system for Pb²⁺was calculated as low as 2.6 nmol?L^-1,which is significantly lower than the 72 nmol?L^-1 specified by the US Environmental Protection Agency?EPA?,and the linear range is 0.02?9.00?mol?L^-1.Furthermore,this method exhibited good specificity and anti-interference by replacing metal ions and adding actual samples of mineral water,green tea and Coptis Chinensis,and the recovery rate is in the range of 95.2%?104.4%.The results demonstrated this method has great application prospects in the actual detection of Pb²⁺.Chapter 3:Detection of Copper Ions by Ratiometric Fluorescent Probe CQDs/GSH-CdTeQDsAiming at the problem that the fluorescence intensity of quantum dots is easily affected by factors?temperature,humidity and light intensity in the environment?,a new method of ratiometric fluorescence detection is proposed.CQDs/GSH-CdTeQDs ratiometric fluorescent probe was prepared by mixed CQDs and GSH-CdTeQDs at a certain ratio.CQDs acted as reference fluorophores and GSH-CdTeQDs acted as detection fluorophores.Ratiometric fluorescence probe can effectively eliminate the interference of external factors and improve the accuracy of detection by using the fluorescence intensity ratio I₆₀₂/I₄₃₈ of two well-resolved emission peaks as a quantitative indicator.The detection limit for Cu²⁺is as low as 0.35 nmol?L^-1,and the linear range is 10 to 100 nmol?L^-1.Moreover,this method shows good specificity and anti-interference by replacing the metal ions.The anti-interference and great application prospects of this method also were tested by adding actual samples of bovine serum,green tea and tap water and recovery rate is in the range of96.2%?104.3%.In addition,this probe exhibited obvious visualizable color change from red to blue by adding different concentrations of Cu²⁺.Chapter 4:Detection of Mercury Ions by Ratiometric Fluorescent Probe g-Cd Td/r-CdTeQDsIn order to further improve the specificity and sensitivity of the ratiometric fluorescent probe for detecting heavy metals,this chapter replaced the reference fluorophore in the ratiometric fluorescent probe with a detection fluorophore that can specifically respond to various heavy metals.Both g-Cd Td QDs and r-CdTeQDs in the probe could produce specific response towards different kinds of heavy metals.Using the fluorescence intensity ratio of g-Cd Td QDs and r-CdTeQDs,which is I₅₁₃/I₅₉₅,as a detection indicator,can significantly improve the specificity and sensitivity to Hg²⁺.The detection limit Hg²⁺is as low as 3.7 nmol?L^-1,and the linear range is 40?500 nmol?L^-1.Moreover,by comparing with single quantum dots?g-Cd Td QDs and r-CdTeQDs?,probe g-Cd Td/r-CdTeQDs showed significantly specificity for Hg²⁺.In addition,the spiked recovery in the actual samples is 90.2%to104.3%,which indicated that this probe has great potential in practical applications.