Synthesis and self-assembly of hierarchical SiO2–QDs@SiO2 nanostructures and their photoluminescence applications for fingerprint detection and cell imaging
Hierarchical SiO2–QDs@SiO2 (QDs = CdTe, PbTe or PbS) nanostructures have been prepared by an integrated synthesis and self-assembly strategy using 3-mercaptopropionic acid (MPA) to stabilize the QDs and NaOH to control the self-assembly of QDs on the SiO2 nanobead carriers. 3–10 nm QDs covered with a 1–2 nm SiO2 shells were separately embedded on the surface of 50 nm SiO2 nanobead carriers, resulting in hierarchical SiO2–QDs@SiO2 nanostructures. MPA and NaOH played important roles in the nucleation and growth of QDs, etching the SiO2 nanobead carriers to the colloidal surface, and the self-assembly of the QDs on viscous SiO2 nanobead carriers. The hierarchical SiO2–QDs@SiO2 nanostructures possess various advantages: (I) the growth of QDs and their self-assembly on SiO2 nanobead carriers were performed in a one-pot reaction by a facile aqueous phase refluxing approach; (II) the SiO2 shell with 1–2 nm in thickness can prevent the leakage of toxic Cd2+ or Pb2+ and avoid photobleaching or environmental pollution; (III) the surface of hierarchical SiO2–QDs@SiO2 nanostructures can be easily functionalized through silane-coupling chemistry. Because of the excellent photoluminescence and biocompatibility, the hierarchical SiO2–QDs@SiO2 nanostructures modified by carboxyl (–COOH) active group can be available for covalent coupling to various biomolecules, which have shown potential applications in fingerprint detection and in vivo cell imaging.