The Synthesis And Analytical Applications Of Mn, Cu Doped ZnS Core-shell Quantum Dots

Semiconductor nanoparticles or quantum dots (QDs) have emerged as the attractive fluorescent probes for detection due to their high fluorescence quantum efficiency, size-dependent broad absorption and readily size-tunable narrow emission as well as photochemical stability compared with the traditional organic fluorescent dye. QDs have been progressed toward different chemical species including ions, drug molecules, organic small molecules and biological macromolecule. We try to study the spectrum of doped-ZnS QDS and explore its application toward the detection small molecules. Below is our content:Chapter 1:This chapter briefly introduced the definition, synthesis, modification and application of QDs and established the study target.Chapter 2:The Mn-doped ZnS core was prepared through a coprecipitation method and a ZnS shell was grown on ZnS:Mn core. The QDs were structurally and compositionally characterized by Infrared Spectroscopy and transmission electron microscopy (TEM). Their Optical properties were investigated by UV-vis absorption spectrum and fluorescence emission spectrum. We also discussed the factors affecting the fluorescence intensity of the nanoparticles. The results showed that: The shape of ZnS:Mn QDs is close to spherical and aggregated. After the growth of the ZnS shell, they show no difference with the core except for their average size. The average size of ZnS:Mn/ZnS core/shell QDs is 4nm. The S-H bond in 3-mercaptopropionic acid of the QDs is covalently bound to Zn on the QDs surface. UV absorption excitonic peak of ZnS:Mn/ZnS is red-shifted copmared with ZnS:Mn. The florescence intensity of ZnS:Mn/ZnS developing an emission peak at 595nm is stronger three times than ZnS:Mn. The optimization factor are Mn doping amount 4%, pH=9.Chapter 3:The ZnS:Cu and ZnS:Cu/ZnS QDs was prepared through a coprecipitation method. The QDs were structurally and compositionally characterized by Infrared Spectroscopy and transmission electron microscopy (TEM). Their Optical properties were investigated by UV-vis absorption spectrum and fluorescence emission spectrum. The results showed that:The shape of ZnS:Cu and ZnS:Cu/ZnS QDs is close to spherical and aggregated. The average size of ZnS:Cu/ZnS core/shell QDs is 3.4 nm which is bigger than the average size of ZnS:Cu 2 nm. The S-H bond in 3-mercaptopropionic acid of the QDs is covalently bound to Zn on the QDs surface. ZnS:Cu solution develops an emission peak at 474 nm. After ZnS shell is coated around the ZnS:Cu core, the fluorescence intensity increases by almost four times with a very slight shift in emission to 481nm, which is likely due to surface Cu sites that were not emissive originally become emissive upon incorporation into the ZnS lattice with further ZnS shell growth. The fluorescence of ZnS:Cu and ZnS:Cu/ZnS QDs is resulted by the radiative transition between ZnS tape and the t2 energy level of Cu. The optimization factor are aged temperature 50℃, pH=10, reflux reaction time 2h.Chapter 4:ZnS:Cu/ZnS and ZnS:Mn/ZnS QDs is filtered firstly. The fluorescence of ZnS:Cu/ZnS could be increased in the presence of uric acid (UA). We have constructed a core/shell ZnS:Cu/ZnS QDs based fluorescence system for UA and successfully applied to determination of UA levels in human urine. The affecting factors for the fluorescence of ZnS:Cu/ZnS were examined including pH, temperature and reacting time. The results showed that:Under the optimized conditions, the fluorescence intensity of the ZnS:Cu/ZnS QDs against the UA concentration showed a linear response in the range of 0.66uM to 3.3μM with the correlation coefficient (R2) 0.9973 and the limit of detection 0.044μM. Most relevant molecules and physiological ions had no effect on the detection of UA. The feasibility of developed method was further demonstrated by determining the concentration of uric acid in human urine samples and the recoveries were 95%～103%. Our work provides a sensitive, selective and low-toxic fluorescence method to determine UA compared with the QDs based detection method for UA.Chapter 5:This chapter study the phosphorescent quenching procedure and mechanism of methyl violet to ZnS:Cu/ZnS and ZnS:Mn/ZnS QDs, which can apply based data to explor the MV and ZnS:Cu/ZnS and ZnS:Mn/ZnS QDs complex material as RTP probes. The results showed that:MV added to the ZnS:Mn/ZnS QDs water solution, the phosphorescent peak in 600nm did not shift but the strength decrease with lifetime decreasing from 1ms to 0.02ms, which have dynamic and static procedure. MV added to the ZnS:Cu/ZnS QDs water solution, the phosphorescent peak in 584nm slightly red shift and the strength decrease with lifetime decreasing from 2ms to 0.01ms, which have dynamic procedure.