The Studies Of New Fluorescence Sensing Asssays Based On Cu:Zn-In-S/ZnS Quantum Dots

Quantum dots, as a new type of fluorescent nanomaterials, have many unique fluorescence properties, which make them play important roles in the field of analytical chemistry. During the past years, quantum dots as a new class of fluorescent probes have gained increasing attentions and were developed rapidly in analytical chemistry. Nevertheless, the common QDs usually compose of toxic heavy-metal elements such as Cadmium, which may bring some further pollutions to our environment. Therefore, researchers have put great efforts on exploring Cadmium-free and environmental friendly QDs for practical applications. In this paper, we aimed at this hot research area and conducted the following works:(1) Synthesis of water-soluble Cu:Zn-In-S/Zn S quantum dots. Oil-soluble Cu:Zn-In-S/Zn S QDs were firstly synthesized and then were transferred into an aqueous solution through the modification of 11-Mercaptoundecanoic acid(MUA). The as-prepared Cu:Zn-In-S/Zn S QDs were characterized by fluorescence photospectroscopy, UV-Visible spectroscopy, infrared spectroscopic, transmission electron microscope, fluorescence images, and X ray diffraction pattern, respectively. In addition, the stability of the QDs in different p H solution as well as their anti-photobleaching ability was investigated. The results showed that the above prepared QDs had good optical properties, which provided a solid foundation for the following experiments.(2) Detection of Hg2+ and Cu2+ based on the fluorescent quenching effect of quantum dots. Several influence factors to the experiment were investigated including buffer, p H values, and reaction time, etc. The relative fluorescence intensity was decreased linearly with the concentration increasing of Hg2+ in the range of 1×10-9 to 1×10-7 mol/L and the limit of detection was 9.6×10-10 mol/L. For Cu2+ analysis, a detection limit of 1×10-9 mol/L was successfully achieved with the linear range of 2.5×10-9 to 7.5×10-8 mol/L. Compared with the reported methods, this approach is environmentally friendly, sensitive, and very simple. Meanwhile, the mechanism of interaction between the metal ions and Cu:Zn-In-S/Zn S QDs were further explored. It was found likely that Hg2+ could bind to MUA on the surface of Cu:Zn-In-S/Zn S QDs, which resulted in the quenching of the fluorescence of QDs. Addition of Cu2+ ions into Cu:Zn-In-S/Zn S QDs might make Zn2+ broken away from Cu:Zn-In-S/Zn S QDs due to the strong affinity of Cu-S, which brought clearly quenching of the fluorescence of QDs.(3) Simple fluorescent sensing of GSH based on fluorescence resonance energy transfer between Cu:Zn-In-S/Zn S QDs and Mn O2 nanosheets. Fluorescence of QDs could be quenched greatly by Mn O2 nanosheet. In the presence of GSH, Mn O2 nanosheets could be reduced into Mn2+ ions. Thus, the ?uorescence of QDs was recovered. A good linear relationship was obtained from 1 to 20 μmol/L for GSH. The detection limit for GSH was 0.5 μmol/L(S/N=3). In addition, the sensing system exhibited a good selectivity for GSH in the presence of other electrolytes and biomolecules. Moreover, GSH standard recovery in serum samples was also demonstrated. We envision that our assay method could facilitate the GSH quanti?cation related biological and biomedical research. Compared with previous reported methods, this quantum dots-based approach is highly selectivity and reliable, which could be used as a new technique for the detection of GSH.(4) Test strip platform for on-site fast detection of Hg2+. By using test strip, the fast detection of Hg2+ was successfully carried out based on the fluorescent quenching effect of quantum dots in the presence of Hg2+. Meanwhile, several influence factors to the experiment were investigated including reaction time and amount of goat-anti human Ig G(Fc) on nitrocellulose membrane. Under optimal experimental conditions, a test strip for on-site detection of Hg2+ was developed. The relative fluorescence intensity decreased linearly with the concentration increasing of Hg2+ in the range of 1×10-9 to 5×10-7 mol/L and the limit of detection was 1×10-10 mol/L. This approach has remarkable advantages such as low-cost, high sensitive and accurate, very simple and fast.