Direct silica-coating of quantum dots

A method for direct silica-coating of fluorescent semiconductor nanoparticles is proposed. The fluorescent semiconductor nanoparticles used are quantum dots (Q-dots), which are CdSe_xTe_1-x nanoparticles coated with ZnS and succeedingly surface-modified with amino groups. The silica-coating was performed in the presence of the Q-dots in 1-15 M H₂O, 0.4 × 10^-4-40 × 10^-4 M NaOH and 0.5 × 10^-4-50 × 10^-4 M tetraethyl orthosilicate (TEOS). Silica shells were formed at 5M H₂O and 4 × 10^-4M NaOH. Under these concentrations of H₂O and NaOH, the particle size of silica-coated Q-dots could be varied from 15.8 to 31.7 nm as the TEOS concentration was increased from 2.5 × 10^-4 to 50 × 10^-4 M. The silica-coated Q-dots showed fluorescence as well as the uncoated Q-dots.