Size-tunable highly luminescent SiO2 particles impregnated with number-adjusted CdTe nanocrystals.

Highly luminescent SiO(2) particles impregnated with CdTe nanocrystals (NCs) are prepared by a sol-gel procedure. Partial ligand exchange from thioglycolic acid to 3-mercaptopropyltrimethoxysilane (MPS) on the NCs enables retention of the initial photoluminescence (PL) efficiency of the NCs in water, while the simultaneous addition of a poor solvent (ethanol) results in regulated assembly of the NCs through condensation of hydrolyzed MPS. The SiO(2) particles thus prepared have, for example, a diameter of 16 nm and contain three NCs each. The PL efficiency of these particles is 40 %, while the initial efficiency is 46 % in a colloidal solution. The redshift and narrowed spectral width in PL observed after impregnation indicate that the concentration of NCs in these nearly reaches the ultimate value (on the order of 10(21) particles per liter). The porosity of these particles is investigated by means of N(2) adsorption-desorption isotherms. Due to the SiO(2) shell, these particles have higher stability in phosphate-buffered saline buffer solution than the initial NCs. Their potential use for labeling in bio-applications is investigated by conjugating biotinylated immunoglobulin G to them by using streptavidin maleimide as linker. Successful conjugation is confirmed by electrophoresis in agarose gel. This preparation method is an important step towards fabricating intensely emitting biocompatible SiO(2) particles impregnated with semiconductor NCs.