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. 2011 Mar 25;115(15):7255-7260.
doi: 10.1021/jp111475y.

Fluorescent Metal Nanoshells: Lifetime-Tunable Molecular Probes in Fluorescent Cell Imaging

Jian Zhang  1 , Yi Fu, Joseph R Lakowicz
Affiliations

Fluorescent Metal Nanoshells: Lifetime-Tunable Molecular Probes in Fluorescent Cell Imaging

Jian Zhang et al. J Phys Chem C Nanomater Interfaces. .

Abstract

We reported the preparation of lifetime-tunable fluorescent metal nanoshells and used them as lifetime imaging agents for potential detection of multiple target molecules by a single cell imaging scan. These metal nanoshells were generated to have 40 nm silica cores and 10 nm silver shells. Three kinds of metal-ligand complexes tris(5-amino-1,10-phenanthroline)ruthenium(II) (Ru(NH(2)-Phen)(3) (2+)), tris(2,2'-bipyridine) ruthenium(II) (Ru(bpy)(3) (2+)), and tris(2,3-bis(2-pyridyl)pyrazine))ruthenium(II) (Ru(dpp)(3) (2+)) that have similar excitation and emission wavelengths but different lifetimes were respectively encapsulated in the cores of metal nanoshells for the purpose of fluorescence. Compared with the metal-free silica spheres, these metal nanoshells were found to display enhanced emission intensities and shortened lifetimes due to near-field interactions of Ru(II) complexes with the metal shells. The shortened lifetimes of these metal nanoshells were definitely unique relevant to the Ru(II) complexes: 10 ns for the Ru(Phen-NH(2))(3) (2+)-Ag nanoshells, 45 ns for the Ru(bpy)(3) (2+)-Ag nanoshells, and 200 ns for the Ru(dpp)(3) (2+)-Ag nanoshells. These lifetimes were longer than the lifetime of cellular autofluorescence (2 - 5 ns), so the emission signals of these metal nanoshells could be distinctly isolated from the cellular background on the lifetime cell images. Moreover, these lifetimes were also different from one another, resulting in the emission signals of three metal nanoshells could be distinguished from one another on the cell images. This feature may offer an opportunity to detect multiple target molecules in a single cell imaging scan when the metal nanoshells are bound with various targets in the cells.

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Figures

Figure 1
Figure 1
Typical single nanoshell fluorescence images for (a) Ru(phen-NH2)32+/silica sphere, (b) Ru(phen-NH2)32+-Ag shell, (c) Ru(bpy)32+/silica sphere, (d) Ru(bpy)32+-Ag shell, (e) Ru(dpp)32+/silica sphere, and (f) Ru(dpp)32+-Ag shell recorded in the emission intensity and lifetime. The scales of diagrams are 5 × 5 μm and the resolutions are 100 × 100 pixel with an integration of 0.6 ms/pixel.
Figure 2
Figure 2
Histograms of emission intensities from (a) Ru(phen-NH2)32+/silica sphere and Ru(phen-NH2)32+-Ag shell, (b) Ru(bpy)32+/silica sphere and Ru(bpy)32+-Ag shell, and (c) Ru(dpp)32+/silica sphere and Ru(dpp)32+-Ag shell.
Figure 3
Figure 3
Histograms of lifetimes from (a) Ru(phen-NH2)32+-Ag shells, (b) Ru(bpy)32+-Ag shells, and (c) Ru(dpp)32+-Ag shells that were collected from the single nanoprobe images.
Figure 4
Figure 4
Representative fluorescence intensity and lifetime images from the single cells (a) blank without dye conjugation, (b) conjugated by Ru(phen-NH2)32+-Ag shells, (c) by Ru(bpy)32+-Ag shells, and by Ru(dpp)32+-Ag shells. The scales of diagrams are 15 × 15 μm. The resolutions of diagrams are 100 × 100 pixel with an integration of 0.6 ms/pixel.
Figure 5
Figure 5
Histograms of lifetimes from the entire images throughout the blank cells without dye conjugation, and the emission spots from the Ru(phen-NH2)32+-Ag shells, Ru(bpy)32+-Ag shells, and Ru(dpp)32+-Ag shells that were conjugated on the cell surfaces.
Figure 6
Figure 6
Representative fluorescence (a) intensity and (b) lifetime cell images conjugated by the Ru(phen-NH2)32+-Ag shells, Ru(bpy)32+-Ag shells, and Ru(dpp)32+-Ag shells upon the excitation at 470 nm. The scales of diagrams are 15 × 15 μm. The resolutions of diagrams are 100 × 100 pixel with an integration of 0.6 ms/pixel.
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