• Graphical abstract: Aqueous phase synthesis of upconversion nanocrystals through layer-by-layer epitaxial growth for in-vivo X-ray computed tomography

  • Fig. 2 (a-e) TEM images of the NaYF4:Yb, Er core and those overcoated with 1-4 layers of the NaGdF4 shell, respectively. (f-j) HRTEM images and their corresponding 3D schematic diagram of the NaYF4:Yb, Er core and those overcoated with 1-4 layers of the NaGdF4 shell, respectively. (k) XRD patterns of NaYF4:Yb, Er core and the corresponding core-shell UCNCs. (l-m) HRTEM and HADDF-STEM images of a single 4-layer NaYF4:Yb, Er@NaGdF4 UCNC. (n) EDS of the 4-layer NaYF4:Yb, Er@NaGdF4 UCNCs.

  • Fig. 3 Room-temperature UC luminescence spectra (a), evolution statistics (b), and photographs of colloidal solutions (c) of ethanol solutions comprising NaYF4: Yb, Er core UCNCs and the corresponding core-shell UCNCs with 1-4 layers of the NaGdF4 shell under excitation with a 980 nm laser. (d-e) UC luminescence decay curves of NaYF4:Yb, Er core UCNCs and the corresponding core4shell UCNCs with 1-4 layers of the NaGdF4 shell.

  • Fig. 4 (a) Room-temperature PL emission spectra of NaYF4:Yb, Er and NaYF4:Yb, Er@NaGdF4:Ce, Ln core–shell NCs. (b) Corresponding Commission Internationale de l’Eclairage (CIE) chromaticity coordinates of the multicolour emissions from the samples shown in (a). (c) Photograph showing physical dimension and transparency of a PDMS sample composed of NaYF4:Yb, Er@NaGdF4:Ce, Ln core-shell NCs. (d-e) Their corresponding bright colour emission under 254 nm UV irradiation and 3D schematic diagram. (f) PL photos showing corresponding colloidal solutions of (a). (g) Energy level diagram and the excitation/emission pathways of the Ln3+ investigated. Only the predominantly observed emission pathways are highlighted. All of the samples’ concentrations were 0.2 M. UC emission spectra were excited using a 600 mW 980 nm diode laser.

  • Fig. 5 (a) Magnetization curves of 1-layer and 4-layer NaYF4:Yb, Er@NaGdF4 core-shell UCNCs. (b) Cell viability of HeLa cells after incubation with increased concentration of 4-layer NaYF4:Yb, Er@NaGdF4 core-shell UCNCs for 24 h. (c) CT value (HU) of NaYF4:Yb, Er core, 1-layer and 4-layer NaYF4:Yb, Er@NaGdF4 core-shell UCNCs as a function of the concentration of core (black trace) 1-layer (red trace) and 4-layer (blue trace), respectively. (d) CT images of solutions of NaYF4: Yb, Er core, 1-layer and 4-layer NaYF4:Yb, Er@NaGdF4 core-shell UCNCs, respectively.

  • Fig. 6 Images of HeLa cells after growing with (a) NaYF4:Yb, Er UCNCs, (b) 4-layer NaYF4:Yb, Er@NaGdF4 core-shell UCNCs for 24 h. Bright field images, confocal fluorescence images and superimposed images are shown, respectively.

  • Fig. 7 In vivo CT coronal view images of a rat after intravenous injection of 1 mL of 4-layer NaYF4:Yb, Er@NaGdF4 core-shell UCNC (448 Gd mg mL1) solution at timed intervals. (a) Spleen and kidney. (b) Liver. (c) The corresponding liver’s 3D renderings of in vivo CT images. (d) Spleen and kidney’s renderings of in vivo CT images.

论文摘要

Lanthanide-doped core–shell upconversion nanocrystals (UCNCs) have tremendous potential for applications in many fields, especially in bio-imaging and medical therapy. As core–shell UCNCs are mostly synthesized in organic solvents, tedious organic–aqueous phase transfer processes are usually needed for their use in bio-applications. Herein, we demonstrate the first example of one-step synthesis of highly luminescent core–shell UCNCs in the “aqueous” phase under mild conditions using innocuous reagents. A microwave-assisted approach allowed for layer-by-layer epitaxial growth of a hydrophilic NaGdF4 shell on NaYF4:Yb, Er cores. During this process, surface defects of the nanocrystals could be gradually passivated by the homogeneous shell deposition, resulting in obvious enhancement in the overall upconversion emission efficiency. In addition, the up-down conversion dual-mode luminescent NaYF4:Yb, Er@NaGdF4:Ce, Ln (Eu, Tb, Sm, Dy) nanocrystals were also synthesized to further validate the successful formation of the core–shell structure. More significantly, based on their superior solubility and stability in water solution, high upconversion efficiency and Gd-doped predominant X-ray absorption, the as-prepared NaYF4:Yb, Er@NaGdF4 core–shell UCNCs exhibited high contrast in in vitro cell imaging and in vivo X-ray computed tomography (CT) imaging, demonstrating great potential as multiplexed luminescent biolabels and CT contrast agents.

论文题目

Aqueous phase synthesis of upconversion nanocrystals through layer-by-layer epitaxial growth for in-vivo X-ray computed tomography

发表刊物
Nanoscale,2013, 5(15),6950-6959.F.Li, C.Li, J.Liu, X.Liu, L.Zhao, T.Bai, Q.Yuan, X.Kong, Y.Han, Z.Shi*, S.Feng
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