PEOlated micelle/silica as dual-layer protection of quantum dots for stable and targeted bioimaging

CdSe/CdS/ZnS quantum dots (QDs) have been successfully encapsulated into poly(ethylene oxide) (PEO)-based polymeric micelle/silica dual layers via interfacial templating condensation. The encapsulation follows a green and straightforward microemulsion mechanism that directly proceeds in a near-neutral pH aqueous environment. No detriment to the optical properties of QDs is observed during encapsulation. The core-shell nanoparticles generated possess a polymeric micelle framework with a single QD encapsulated in the hydrophobic micellar core, an ultrathin (<5 nm in thickness) yet robust silica shell confined to the micellar core/corona interface and free PEO chains dangling on the surface. The free PEO chains effectively prevent nonspecific adsorption of biomolecules to the nanoparticles. Double shielding of polymeric micelle/silica shell remarkably improves the fluorescence resistance of QDs to strong acids and highly salted buffers. In vitro testing using MDA-MB-231 breast cancer cells demonstrates that these organic/inorganic dual layer-protected QDs conjugated with folate show noncytotoxicity and bright fluorescence cellular imaging with high target specificity.