Optical Sensor Based On CdTe Quantum Dots For Detection Of Sodium Cromoglycate, Zn(Ⅱ) And DNA

Quantum dots（QDs） are usually used as optical probe in sensor due to its unique optical properties. In this study, glutathione（GSH） modified CdTe QDs were firstly synthesized in aqueous solution and characterized by transmission electron microscope（TEM）, ultraviolet-visible absorption（UV-vis） spectra, fluorescence spectra and resonance Rayleigh scattering（RRS） spectra. Then a novel fluorescence probe for determination of sodium cromoglycate based on fluorescence quenching of CdTe quantum dots was developed; fluorescence nanoswitch for detection of Zn（II） based on quantum dot/diethylenetriaminepentaacetic acid was constructed; dual-wavelength overlapping resonance Rayleigh scattering and fluorescence platform for detection of DNA based on quantum dot/diminazene aceturate system was designed. In addition, the reaction mechanism of the system were also discussed in detail by ultraviolet-visible absorption spectra, fluorescence spectra, resonance Rayleigh scattering spectra, thermodynamic calculation, and quantum chemistry calculation method. The main context was shown below: 1 Determination of sodium cromoglycate based on fluorescence quenching of CdTe quantum dotsA sensitive and simple analytical strategy for the detection of sodium cromoglycate（SCG） has been established based on electron transfer mechanism and fluorescence quenching effect of SCG for CdTe quantum dots（QDs）. In this system, SCG served as an efficient electron acceptor. Adding SCG to the solution of CdTe QDs, electron transfer proceed from the condution band of CdTe QDs to SCG, which prevented the electron-hole recombination and caused the fluorescence quenching of CdTe QDs. Under the optimum conditions, The degree of fluorescence quenching of CdTe QDs was linearly proportional to the concentration of SCG between 0.6419 μg·m L^-1 and 100 μg·mL^-1, with detection limit of 0.1926 μg·mL^-1. Furthermore, the reaction mechanism, experimental conditions and the influences of coexisting foreign substances on the reaction were also investigated. The established method has been successfully applied to the determination of SCG in its synthetic samples and real samples. 2 A regenerable fluorescence nanoswitch based on CdTe quantum dots for monitoring Zn（II） in aqueous solutionGlutathione（GSH） modified CdTe QDs were synthesized in aqueous solution. The study found diethylenetriaminepentaacetic acid（DTPA） could be combined with the GSH on the surface of the CdTe QDs through hydrogen bonds, forming CdTe QDs-DTPA complex, which resulted in the fluorescence quenching of CdTe QDs; adding Zn²⁺ to the solution, the strong chelation between DTPA and Zn²⁺ enabled the DTPA to be detached from the surface of CdTe QDs to form a more stable complex with Zn²⁺, thereby restoring the fluorescence of CdTe QDs. So we constructed a simple, sensitive and regenerable fluorescent nanoprobe for the determination of Zn²⁺. Under optimum conditions, the intensity of the restored fluorescence was proportional to the concentration of Zn²⁺ in the 0.48 to 90 μmol·L^-1 range, with a limit of detection of 0.14 μmol·L^-1. The nanoprobe was applied to the determination of Zn²⁺ in spiked tap water and river water and gave satisfactory results. Meanwhile, the reaction mechanism, experimental conditions and the influences of coexisting foreign substances on the reaction were also investigated. 3 Dual-wavelength overlapping resonance Rayleigh scattering and fluorescence platform for detection of DNA based on quantum dot/diminazene aceturate systemA new dual-wavelength overlapping resonance Rayleigh scattering（DWO-RRS） and fluorescence platform has been designed for detection of DNA based on quantum dots（QDs） and diminazene aceturate（DA） system. In the absence of DNA, QDs and DA formed a complex through electrostatic interaction, which resulted in the RRS intensity getting enhanced significantly with new RRS peaks appearing at 322 and 420 nm; the fluorescence was quenched. In the presence of DNA, competitive binding occurred between QDs and DNA toward DA; then, DA was gradually released from the QDs/DA complex, causing obvious decrease of the RRS and enhancement of the fluorescence. The scattering intensities of the two peaks were proportional to the concentration of DNA in the range of 0.030^-15 μg·m L^-1. The detection limits of the DWO-RRS method was 0.0089 μg·mL^-1. Besides, the fluorescence sensing system also exhibited good linear range from 0.046-24 μg·mL^-1 with a detection limit as low as 0.0139 μg·m L^-1. This platform combined the advantages of the DWO-RRS and fluorescence. More importantly, monitoring simultaneously the RRS and fluorescence signals can conduce to increase the accuracy for detection. Additionly, the two optical signals can be achieved on a fluorescence spectrophotometer in different modes, thus experimental procedures were greatly simplified. Finally, the sensor has been applied to the detection of DNA in human serum with satisfactory results.