Synthesis and Properties of Biocompatible Water-Soluble Silica-Coated CdSe/ZnS Semiconductor Quantum Dots

TLDR

The study reports the synthesis of water‑soluble CdSe/ZnS quantum dots and aims to enable their conjugation to biological entities via functionalized siloxane surfaces. They embed 2–5 nm CdSe/ZnS core/shell nanocrystals in a siloxane shell and functionalize the surface with thiol and/or amine groups to render the particles water‑soluble. AFM reveals a 1–5 nm siloxane shell yielding 6–17 nm particles, while the silica coating preserves optical properties, giving 32–35 nm FWHM emission tunable from blue to red with quantum yields up to 18 %, and confers superior photochemical and physiological buffer stability compared to organic fluorophores.

Abstract

We describe the synthesis of water-soluble semiconductor nanoparticles and discuss and characterize their properties. Hydrophobic CdSe/ZnS core/shell nanocrystals with a core size between 2 and 5 nm are embedded in a siloxane shell and functionalized with thiol and/or amine groups. Structural characterization by AFM indicates that the siloxane shell is 1−5 nm thick, yielding final particle sizes of 6−17 nm, depending on the initial CdSe core size. The silica coating does not significantly modify the optical properties of the nanocrystals. Their fluorescence emission is about 32−35 nm fwhm and can be tuned from blue to red with quantum yields up to 18%, mainly determined by the quantum yield of the underlying CdSe/ZnS nanocrystals. Silanized nanocrystals exhibit enhanced photochemical stability over organic fluorophores. They also display high stability in buffers at physiological conditions (>150 mM NaCl). The introduction of functionalized groups onto the siloxane surface would permit the conjugation of the nanocrystals to biological entities.