Study on the Luminescence Stability of CdSe/CdxZn1-xS Quantum Dots During the Silication Process

CdSe/CdxZn1-xS core-shell quantum dots capped with oleic acid have been encapsulated into SiO2 nanospheres by a modified reverse microemulsion method. As an effective approach to convert quantum dots with nonpolar capping agent into hydrophilic and biocompatible ones, silica coating technology is limited by the inevitable luminescence degradation during the silication process. CdxZn1-xS shell involved to protect CdSe core quantum dots from luminescence quenching was found to be quite helpful to restrain the luminescence degradation during the silica coating process. The luminescent intensity has been highly enhanced by controlling the thickness of CdxZn1-xS shells. Luminescence quenching has also been observed when the as-prepared silica coated quantum dots were transferred from the reaction solution into different solvent. According to the time-resolved luminescence and stability examination, the micro channels in the SiO2 shells should be responsible for the degradation. Polyethylene glycol has thus been introduced to block the channel, resulting in a product with much higher emission efficiency, which performed well as a fluorescent labeling probe for MCF-7 cells.