Surface modification of SiO2 beads with multiple hydrophobic quantum dots for bioapplications

Multi hydrophobic CdSe/ZnS or CdSe/CdxZn1 − xS quantum dots were encapsulated into SiO2 beads through a three-step sol–gel procedure. First, the quantum dots were transferred from toluene to water phase via silanization using tetraethyl orthosilicate. The control of ligand exchange (partially hydrolyzed tetraethyl orthosilicate instead of organic amine) resulted in the quantum dots retaining their initial photoluminescence efficiencies after the phase transfer. Second, the assembly of the quantum dots occurs by the hydrolysis and condensation of tetraethyl orthosilicate to form seeds. The amount of 3-mercaptopropyltrimethoxysilane during incorporation plays an important role in controlling the quantum dot number per seed. Third, the seeds are coated with a SiO2 shell by a subsequent Stöber process. The resulting SiO2 beads with a controlled number of hydrophobic quantum dots revealed high photoluminescence efficiency. The SiO2 beads were functionalized with amine, carboxyl, and thiol-terminated biolinkers for surface modification. To confirm the surface modification by carboxyl groups, the SiO2 beads were conjugated with amino functional polystyrene beads. The silica beads introduced here represent a new platform for nanoparticulate multimodality bioanalysis.