SiO2 beads with quantum dots: Preparation and stability investigation for bioapplications

SiO 2 beads with quantum dots (QDs) including hydrophilic CdTe or hydrophobic CdSe/ZnS were prepared through sol–gel procedures. These beads contained single or multiple QDs by controlling the ligand exchange and the QD assembly during incorporation. Namely, SiO 2 beads with CdTe QDs retained high photoluminescence (PL) efficiencies up to 40% when thioglycolic acid was partially replaced by 3-mercaptopropyltrimethoxysilane. Multiple CdSe/ZnS QDs were assembled into a SiO 2 bead (∼7 QDs in each bead) through surface silanization using tetraethyl orthosilicate instead of organic ammine. The stability of CdTe QDs and luminescent SiO 2 beads was investigated by measuring the degradation of PL intensity against the concentration of phosphate-buffered saline (PBS) buffer solutions. The Stern–Volmer quenching constant K sv of QDs depended strongly on the properties of the QDs and the thickness and porous type of SiO 2 shell. Red- and green-emitting CdTe QDs exhibited K sv of 2.02 × 10 −2 and 8.93 × 10 −2 mM −1 , respectively. The II-type pores (cylindrical pores) in the SiO 2 shell resulted in quick degradation while the IV-type pores (ink-bottle-shaped pores) led the QDs a high stability. Because both two kinds of QDs in SiO 2 beads revealed high PL efficiency and stability in buffer solution, these luminescent beads should be utilizable for bioapplications.