Aqueous Synthesis, Characterization And Application Of Cd_xZn_1-xTe Alloyed Quantum Dots

Semiconductor nano-crystals or quantum dots (QDs) have shown their tremendous potential for applications in biomedical areas especially in biomedical labeling, fluorescent bio-probe and so on. Water-based preparation of QDs has become one of the most attractive points because of the requirement of their applications in biomedical areas. Recently, synthesis of binary QDs or core-shell structured QDs in aqueous solution has achieved great progress while the synthesis of water-soluble alloyed QDs still has its limitation. Moreover, alloyed QDs prepared through aqueous route mostly have tunable emission wavelength within blue or near-infrared range, which lack of counterparts with both high photoluminescence quantum yield (PL QY) and visible-light-emitting spectra.In this paper, both two-step process and one-step process synthetic methods were used to prepare water-soluble CdZnTe alloyed QDs with glutathione (GSH) as stabilizer. As for the two-step process method, ZnTe nanocrystal seeds were prepared firstly, and then Cd precursor was added to synthesize CdZnTe alloyed QDs. However, in the one-step process method, Cd, Zn, and Te precursors were mixed simultaneously to synthesize CdZnTe alloyed QDs. With these two methods, GSH-CdZnTe alloyed QDs with fluorescent emission wavelength range from 470 to 605nm could be obtained, and their QYs could reach up to 75%. Furthermore, we systemically investigated the influences of reaction time, molar ratio of precursor and pH value on the fluorescent properties of CdZnTe QDs. According to the results, drawbacks such as inconvenient experimental procedure or poor reproducibility in the two-step process limited the performance of the products. Besides, the optical properties of as-prepared CdZnTe alloyed QDs were influenced by the growth status and the lattice defects of ZnTe nanocrystal seeds. However, one-step process was relative simple and reproducible, and the QYs of CdZnTe alloyed QDs could be higher than 50% in the wide wavelength range of 480-590nm by optimizing the reaction parameters.Moreover, GSH, as one of the most abundantly exist detoxification ingredient in human body, was proved to have strong chelation with heavy metal ions. Hence, after mixing GSH-capped QDs and heavy metal ions, the competitive binding of GSH with heavy metal ion and the QDs would change both the surfaces and the photophysical properties of the QDs. In our experiment, the as-prepared GSH-capped CdZnTe alloyed QDs with different concentration were utilized for the detection of free Pb2+ or Hg2+ ion. According to our results, the concentration of CdZnTe QDs of 0.5μM was reasonable, and it was sensitive to detect the concentration of Pb2+ ion of 10nM with stable reduction amplitude of 22% in its fluorescent intensity, and the concentration of Hg2+ ion of 25nM with 20% reduction correspondingly. Obviously, our detection system composed of GSH-capped CdxZn1-xTe alloyed QDs and a common fluorophotometer suggested its promising application on heavy metal ion detection.