Design and Fabrication of a Geometrically Ordered Hydrophobic Interlayer to Prepare High-Quality QD/SiO2 for Cell Imaging

The use of silica coatings has been a popular approach for the fabrication of water-soluble and biocompatible surfaces of quantum dots (QDs). However, most methods presently used cause a significant decrease in QD photoluminescence (PL), hampering further applications in biological and clinical research. We report a convenient method for the preparation of silica-shelled CdSeS/ZnS QDs (QD/SiO2) with a single semiconductor core and a high PL quantum yield (QY) in water (similar to 0.94, more than twice that of uncoated QDs in chloroform (similar to 0.44)). In our approach, a hydrophobic interlayer surrounding the CdSeS/ZnS nanocrystal core was fabricated prior to silanization. This allowed for optimization of intermolecular assembly between surfactants, and the geometric optimization of silane precursors and their initial coordinating ligands, by modulating their alkyl chain lengths. The resulting, geometrically well-matched interlayer exhibited higher hydrophobicity and lower molecular motility, both of which have been shown to enhance QY. QD/SiO2 surfaces, functionalized with triphenylphosphine, yielded targeted, high-quality fluorescent images of mitochondria in live cells.