The Research On Quantum Dots As Ion/Bioprobes And One Pot Synthesis Of Silica-Coated CdTe Quantum Dots

This thesis describes the unique optical properties of quantum dots (qdots), current approaches for the synthesis of qdots and their applications on life science research. CdTe qdots were synthesized directly in aqueous solution by using thioglycolic acid (TGA) or cysteamine (MA) as the stabilizer. Based on TGA-modified qdots, a new approach was developed for sensitive and selective determination of copper ions. In order to improve the stability of MA-modified qdots, silica layer was added to each individual quantum dot. Furthermore, the silica-coated qdots were successfully used to the cells labelling. Meanwhile, a new one-pot approach was proposed for the first time to prepare silica-coated qdots. (1) CdTe qdots were synthesized in aqueous solution by using TGA as the stabilizer. They were characterized by UV-Vis, fluorescence spectroscopy and AFM, respectively. With this kind of water-soluble qdots as fluorescence probes, a novel approach was developed for sensitive and selective determination of copper ions. Different influence factors were studied, including the buffer concentration, qdots concentration, pH values and reaction time. Under the optimized conditions, the relative fluorescence intensity decreased linearly with the copper ions concentration in the range from 2 to 200μg·L^-1 and the detection limit could reach 0.29μg·L^-1. Based on the charge-transfer quenching mechanism, the copper ions bounding onto the surface of qdots could absorb electrons from valance band, which results in the quenching of fluorescence. This was proved by photolysis experiment. (2) The MA-capped CdTe qdots were prepared in aqueous solution, and then characterized by UV-Vis and fluorescence spectroscopy. In order to improve the stability of this kind of qdots, a thin silica layer was covalently bound to the surface of every particle to prepare silica-coated qdots. Amine and phosphonate groups were modified on their surface simultaneously. The qdots after coating was monodisperse and well separated. Various reaction conditions that affected the properties of silica-coated qdots were studied, including ligand-exchange time, the dosage of TEOS and the reaction temperature. Furthermore, the silica-coated qdots were characterized by a series of techniques, such as fluorescence spectra, AFM, size distributions, Zeta potential and photobleaching, etc. Moreover, it was successfully linked with lactobionic acid through amine groups on the surface of particles, and used to recognize living liver cells successfully. (3) In order to simplify the proceeding of preparation of silica-coated qdots, a novel one-pot method using 3-mercaptopropyl-trimethoxysilane (MPS) as a capping molecule was proposed for the first time. Furthermore, amine and phosphonate groups were also modified on the surface of silica-coated qdots simultaneously. This was the first time the synthesis and the surface modification of qdots were performed in the same system. The effects of MPS concentration, pH values and reaction temperature on emission properties were investigated. A series of techniques, including fluorescence spectra, AFM, size distributions, Zeta potential and photobleaching, were used to characterize this kind of products.