SiO2 Beads with Quantum Dots: Synthesis and Bioapplication
Aqueous CdTe and organic CdSe/ZnS quantum dots (QDs) were encapsulated into SiO2 beads using various controlled sol-gel processes. Ligand exchange is a key to adjust the QD number in each bead and get a high photoluminescence (PL). Namely, partial ligand exchange from thioglycolic acid to 3-mercaptopropyotrimethoxysilane (MPS) on the CdTe QDs enables retention of the initial PL efficiency of the QDs in water, while the simultaneous addition of a poor solvent (ethanol) resulted in regulated assembly of the QDs through condensation of hydrolyzed MPS. SiO2 beads thus prepared had, for example, a diameter of 17 nm and contained 3 QDs each. The PL efficiency of these beads was 30%, while the initial PL efficiency was 38% in a colloidal solution. In addition, a method including surface silanization, phase transfer and self-assembly, and SiO2 shell growth has been developed to incorporate multiple hydrophobic CdSe/ZnS QDs into SiO2 beads where they are well suited for bio-application due to their high brightness, less-cytotoxic, and non-blinking nature. To investigate the potential use for labeling in bio-applications, SiO2 beads with multiple QDs were conjugated with IgG using streptavidin-maleimide as linkers. This preparation method is an important step towards fabricating intensely emitting biocompatible SiO2 beads impregnated with semiconductor QDs.
Shiquan Liu and Min Zuo
P. Yang et al., "SiO2 Beads with Quantum Dots: Synthesis and Bioapplication", Advanced Materials Research, Vols. 306-307, pp. 16-19, 2011