Phase transfer of hydrophobic QDs for water-soluble and biocompatible nature through silanization

A novel method has been developed for creating water-soluble and biocompatible CdSe/ZnS quantum dots (QDs) with a small hydrodynamic diameter (less than 10 nm). The silanization of the QDs was carried out by using partially hydrolyzed tetraethyl orthosilicate (TEOS) to replace organic ammine or tri-n-octylphosphine oxide on the surface of the QDs. The partially hydrolyzed 3-mercaptopropyltrimethoxysilane attached to the hydrolyzed TEOS layer on the QDs prevented the QDs from agglomeration when the QDs were transferred into water. The functional SiO2-coated QDs were conjugated with immunoglobin G antibody by using biotin–streptavidin as linkers. The SiO2-coated QDs exhibited the same absorption and photoluminescence (PL) spectra as those of initial QDs in organic solvents. The SiO2-coated QDs preserved PL intensities, is colloidally stable over a wide pH range (pH 6–11). Because the mean diameter of amphiphilic polymer-coated QDs was almost 2 times of that of functional SiO2-coated QDs, the QD phase transfer by silanization is a well-established method for generating biocompatible QDs.