The Synthesis Of Mn Modified CdTe/CdS Core-shell Quantum Dots And Its Application To Detect Trace Copper In Food Samples

Copper is one of trace essential elements, but it becomes toxic if eaten inexcessive amounts. It can injury the cell membrane and restrain the activities of someenzyme inducing the damage of metabolism, and induce the cardiovascular systemdisease. Due to copper with low concentration level widely existing in daily food, it isessential to establish the sensitive, selective and rapid analytical methods for thedetection of trace copper in food.Quantum dots （QDs）, as new fluorescence probes, are increasingly developed tomeet the need of modern analytical techniques. Due to their excellent opticalproperties, high photoluminescence quantum yields （PLQYs） and narrow andsymmetry, QDs have been widely used for trace copper detection in food. However,the PLQYs of naked QDs were low because of many defects on the surface of QDs,which would affect the detective sensitivity of trace copper. How to synthesize QDsof high PLQYs and use them as Cu²⁺fluorescence probes for trace copper detectionin food remains to be a problem.In this research paper, the novel Mn modified CdTe/CdS QDs of high PLQYswere synthesized and were used as Cu²⁺fluorescence probes for trace copperdetection in food. The detailed novelty of this research can be categorized asfollowing:1. Water-soluble MPA capped CdTe QDs were synthesized. However, a largenumber of defects were existing on the surface of naked CdTe QDs, so widerband-gap material CdS was capped and manganese was modified on the surface ofCdTe/CdS QDs, resulting in high PLQYs. The as-synthesized Mn modifiedCdTe/CdS QDs presented high PLQYs of84％. The transmission electronmicroscopic image showed that Mn modified CdTe/CdS QDs were nearly sphericaland monodispersed and the average size of the particles was about5nm. The X-ray diffraction patterns of Mn modified CdTe/CdS QDs showed representative diffractivepeak for nanoparticles, which indicated a good crystal structure.2. A new method for trace copper detection was established based on fluorescencequenching effect of Cu²⁺to Mn modified CdTe/CdS QDs. The pH value, QDsconcentration and stabilization time were investigated to be influencing factors ofCu²⁺—Mn modified CdTe/CdS QDs fluorescence quenching system. Compared withCdTe QDs and CdTe/CdS QDs, Mn modified CdTe/CdS QDs showed the highestdetective sensitivity for Cu²⁺. The interference study demonstrated that Mn modifiedCdTe/CdS QDs as fluorescence probes for Cu²⁺detection possessed high selection.The results showed that the optimal pH value was in the range of7.0～7.5and theoptimal concentration of Mn modified CdTe/CdS QDs was1.25×10^-7mol L^-1. Thecalibration curve showed good linearity with correlation coefficient of0.9991in theconcentration range of5.0×10^-9～5×10^-7mol L^-1of Cu²⁺. The limit of detection was2.7×10^-9mol L^-1. The method built was exploited to analyze trace copper in beers,juices, coffees and white wines. The spiked recoveries of Cu²⁺were in the range of88.64%-109.2%with relative standard deviation≤9.15%.