The Synthesis And Fluorescence Sensing Application Of CdTe Quantum Dots Coated With Cysteamine

Quantum dots(QDs), as new nanometer fluorescence probe, have distinguished intrinsic properties such as wide absorption spectrum, narrow band emission, high fluorescence quantum yield, large surface-to-volume ratio and surface functionality. QDs get extensive attention in fluorescence sensing analysis. In order to improve the sensitivity and selectivity of QDs in fluorescent sensor, QDs are modified through surface functionality. Cysteamine(CA) is a kind of thiol amine compounds. The mercapto group of CA can coordinate with the center metal atoms of QDs. The amino of CA make the materials possess good water solubility, surface positively-charge. However, the research of fluorescent sensors based on QDs coated with CA is not a lot. In this article, CA was chosen as stabilizer. Cd Te QDs coated with CA were prepared and used as fluorescence sensor. Three types of fluorescence sensing systems were designed to detect tartrazine, crystal violet and L-ascorbic acid respectively. Concrete research content is as follows:(1) The preparation of CA-Cd Te QDs. In this experiment, CA-Cd Te QDs were synthesized successfully by reflux method with Na HTe as precursor, Cd Cl2 as cadmium source, CA as modifier. The CA-Cd Te QDs were characterized by UV-Visible spectroscopy, fluorescence spectroscopy, infrared spectroscopy, TEM, XRD, particle size distribution and Zeta potential determination methods. The results showed that the surface of the CA-Cd Te QDs possessed the cubic crystal system structure, infrared absorption with amino groups. The surface of QDs had positively-charge. The max emission wavelength of CA-Cd Te QDs was in the range of 523- 577 nm. The QDs had good fluorescent emission performance, small particle size, uniform distribution and high photo-stability. CA-Cd Te QDs had certain tolerance to the acid alkali of solution.(2) Determination of tartrazine by fluorescence directly quenching method based on the CA-Cd Te QDs. In weak alkaline solution, the fluorescence intensity of CA-Cd Te QDs was quenched by tartrazine through electrostatic effect. The surface state of the QDs changed and fluorescence intensity was reduced. In this experiment, simple rapid fluorescence sensor for determining tartrazine was established based on fluorescence directly quenching method. Under the optimum experimental condition, the linear range of detection system was 8.0- 800 nmol·L-1, the detection limit was 5.5 nmol·L-1. In comparison with other reported methods, this method had excellent sensitivity and selectivity. Common metal ions and pigments didn’t interfere with this system. The method was used for the determination of tartrazine in drinks with satisfactory results.(3) Determination of crystal violet by fluorescence resonance energy transfer quenching method based on the CA-Cd Te QDs. There was a lot of overlap between the absorption spectrum of Crystal violet and fluorescence emission spectrum of CA-Cd Te QDs(8h). With the action of sodium polystyrene sulfonate(PSS), the fluorescence resonance energy transfer sensing system was established through electrostatic effect between PSS, Crystal violet and Crystal violet. The fluorescence of CA-Cd Te QDs was quenched by crystal violet through fluorescence resonance energy transfer. Under the best experimental condition, the concentration of Crystal violet fluorescence had good linear relationship with the efficiency of fluorescence resonance energy transfer in the range of 0.04- 1.0 μmol·L-1, the detection limit was 13 nmol·L-1. The method was used for the determination of crystal violet in the lake with satisfactory results.(4) Determination of L-ascorbic acid by fluorescence off-on method based on the CA-Cd Te QDs. Ce4+ reacted with CA-Cd Te QDs, the surface state of QDs changed, and the fluorescence quenched. Ascorbic acid restored Ce4+ as Ce3+ with strong reducibility. So the fluorescent of QDs recovered. Under the best experimental condition, the degree of fluorescence restoration had good linear relationship with the concentration of ascorbic acid in the range of 0.033- 33 μmol·L-1, the detection limit was 0.011 μmol·L-1. In comparison with other reported methods, this method had excellent sensitivity and selectivity. Common metal ions, amino acids and proteins of blood sample didn’t interfere with this system. The method was used for the determination of L-ascorbic acid in serum with satisfactory results.