Silica coating is an effective approach for rendering luminescent quantum dots (QDs) with water dispersibility and biocompatibility. However, it is still challenging to prepare silica-coated QDs (QD@SiO2) with high emission efficiency, small size and great stability in favor for bioapplication. Herein, we reported a modified Stober method for silica coating of aqueously-prepared CdTe/CdS QDs. With the coexistence of Cd2+ and thioglycolic acid (TGA), a thin silica shell was formed around QDs by the hydrolysis of tetraethyl orthosilicate (TEOS). The resultant QD@SiO2 with a small size (similar to 5 nm in diameter) exhibits significantly higher emission efficiencies than that of the initial QDs. Also, QD@SiO2 has extraordinary photo and colloidal stability (pH range of 5-13,4.0 M NaCl solution). Protected by the silica shell, the cytotoxicity of QDs could be reduced. Moreover, the QD@SiO2 conjugated with folic acid (FA) presents high specific binding toward receptor-positive HeLa cells over receptor-negative A549 cells. (C) 2014 Elsevier Ltd. All rights reserved.