Single quantum dot-micelles coated with silica shell as potentially non-cytotoxic fluorescent cell tracers

The present study describes a stabilization of single quantum dot (QD) micelles by hydrophobic silica precursors and an extension of the silica layer to form a silica shell around the micelle. The obtained product consists of up to 92% of single nanocrystals (CdSe, CdSe/ZnS, or CdSe/ZnSe/ZnS quantum dots) in the silica micelles, coated with silica shell. The thickness of silica shell could vary, starting from 3 to 4 nm. Increasing the shell thickness increases the photoluminescent characteristics of QDs in aqueous solution. The silica-shelled single CdSe/ZnS QD micelles possess a high quantum yield in aqueous solution, a controlled small size, sharp photoluminescence spectra (fwhm approximately 30 nm), an absence of aggregation, and a high transparency. The presence of a hydrophobic layer between the QD and silica shell ensures an incorporation of other hydrophobic molecules (with interesting properties) in the close proximity of nanocrystal. Thus, it is possible to combine the characteristics of hybrid material with the priority of small size. The nanoparticles are amino functionalized and ready for conjugation. A comparatively good biocompatibility is demonstrated. The nanoparticles show ability for intracellular delivery and are noncytotoxic during long-term incubation with viable cells in the absence of light exposure, which makes them appropriate for cell tracing and drug delivery.