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Magneto-fluorescent core-shell supernanoparticles.

Chen O, Riedemann L, Etoc F, Herrmann H, Coppey M, Barch M, Farrar CT, Zhao J, Bruns OT, Wei H, Guo P, Cui J, Jensen R, Chen Y, Harris DK, Cordero JM, Wang Z, Jasanoff A, Fukumura D, Reimer R, Dahan M, Jain RK, Bawendi MG - Nat Commun (2014)

Bottom Line: A thin layer of silica coating provides high colloidal stability and biocompatibility, and a versatile surface functionality.We demonstrate that after surface pegylation, these silica-coated magneto-fluorescent supernanoparticles can be magnetically manipulated inside living cells while being optically tracked.Moreover, our silica-coated magneto-fluorescent supernanoparticles can also serve as an in vivo multi-photon and magnetic resonance dual-modal imaging probe.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.

ABSTRACT
Magneto-fluorescent particles have been recognized as an emerging class of materials that exhibit great potential in advanced applications. However, synthesizing such magneto-fluorescent nanomaterials that simultaneously exhibit uniform and tunable sizes, high magnetic content loading, maximized fluorophore coverage at the surface and a versatile surface functionality has proven challenging. Here we report a simple approach for co-assembling magnetic nanoparticles with fluorescent quantum dots to form colloidal magneto-fluorescent supernanoparticles. Importantly, these supernanoparticles exhibit a superstructure consisting of a close-packed magnetic nanoparticle 'core', which is fully surrounded by a 'shell' of fluorescent quantum dots. A thin layer of silica coating provides high colloidal stability and biocompatibility, and a versatile surface functionality. We demonstrate that after surface pegylation, these silica-coated magneto-fluorescent supernanoparticles can be magnetically manipulated inside living cells while being optically tracked. Moreover, our silica-coated magneto-fluorescent supernanoparticles can also serve as an in vivo multi-photon and magnetic resonance dual-modal imaging probe.

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Silica-coated CS-SPsa, A representative TEM image of silica-coated CS-SPs (silica-CS-SPs) with a thin layer thickness of ~ 10.6 ± 0.7 nm. Scale bar is 200 nm. Insets show the histogram of the particle diameter distribution of silica-CS-SPs with an average diameter of 100 ± 12 nm (top right) and a zoomed-in TEM image of one silica-CS-SP (bottom right). Scale bar in the inset is 50 nm. b, An image of dark-field scanning TEM (STEM) and elemental line scan from a silica-CS-SP show that, while maintaining the core-shell superstructure, a thin layer of silica shell is uniformly deposited onto the CS-SP’s surface. Scale bar is 50 nm. c, HD diameter and relative photoluminescence (relat. PL) intensity of silica-CS-SPs as a function of storage time. d, Magnetic characterization (magnetization versus magnetic field at 300K) shows the superparamagnetism of silica-CS-SPs. e, Left, epi fluorescence image of silica-CS-SPs on a glass substrate. Right, a representative photoluminescence time trace of a single silica-CS-SP.
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Figure 3: Silica-coated CS-SPsa, A representative TEM image of silica-coated CS-SPs (silica-CS-SPs) with a thin layer thickness of ~ 10.6 ± 0.7 nm. Scale bar is 200 nm. Insets show the histogram of the particle diameter distribution of silica-CS-SPs with an average diameter of 100 ± 12 nm (top right) and a zoomed-in TEM image of one silica-CS-SP (bottom right). Scale bar in the inset is 50 nm. b, An image of dark-field scanning TEM (STEM) and elemental line scan from a silica-CS-SP show that, while maintaining the core-shell superstructure, a thin layer of silica shell is uniformly deposited onto the CS-SP’s surface. Scale bar is 50 nm. c, HD diameter and relative photoluminescence (relat. PL) intensity of silica-CS-SPs as a function of storage time. d, Magnetic characterization (magnetization versus magnetic field at 300K) shows the superparamagnetism of silica-CS-SPs. e, Left, epi fluorescence image of silica-CS-SPs on a glass substrate. Right, a representative photoluminescence time trace of a single silica-CS-SP.

Mentions: With their combination of both magnetism and fluorescence, CS-SPs have potential in various applications and technological devices. However, feasible applications, especially in biological systems, often require additional surface functionality, and this can be significantly hindered with CS-SPs that have a PVP polymer surface. To overcome this challenge and improve biocompatibility and colloidal stability, we encapsulate CS-SPs (~ 80 nm) with a thin silica shell through a sol-gel process38, 39. TEM characterization shows that each CS-SP is uniformly coated with a 10.6 ± 0.7 nm thick silica shell (Fig. 3a). STEM line scan, element mapping and 3D TEM tomography show that the core-shell superstructure is preserved (Fig. 3b, Supplementary Fig. 6 and Supplementary Movie 3). DLS measurements reveal that the HD diameter dramatically decreases from ~ 130 nm to ~ 100 nm, similar to the TEM-determined size of ~100 nm (Fig. 3a and Supplementary Fig. 7). The decrease in HD size implies a complete removal of the bulky PVP layer. Importantly, these silica-coated CS-SPs (silica-CS-SPs) display a high degree of colloidal stability. No measureable changes in both the PL intensity and HD size can be observed after 6-month at 4 °C (Fig. 3c). These silica-CS-SPs exhibit superparamagnetism at room temperature with a saturation magnetization of 15.2 emu g−1 (1.4 × 10−14 emu per particle) (Fig. 3d and Supplementary Fig. 8 and Supplementary Table 3). The decreased magnetization compared to that of free Fe3O4 MNPs (63.7 emu g−1, Supplementary Fig. 9) is due to non-magnetic components inside each silica-CS-SP (the QDs, the silica layer, and the organic ligands) with a mass percentage of 75.2% (Supplementary Fig. 10 and Supplementary Table 3). The PL QY of the silica-CS-SPs was measured to be ~12% using a 405 nm excitation light, comparable with that of the PVP-coated CS-SPs (Supplementary Fig. 11). The decreased QY compared to free QDs (PL QY of 94%) is in large part a result of the MNPs strongly absorbing this wavelength light. Under the illumination of a continuous wave laser at a power density of 22 W cm−2 for ~ 2800 second, silica-CS-SPs did not show evidence either of blinking or photo-bleaching (Fig. 3e), thus making them an ideal tool for single particle tracking. To demonstrate the silica-layer enabled surface functionality, methoxy-polyethylene-glycol silane (mPEG-silane, MW5000) was conjugated to the CS-SPs (Supplementary Fig. 12). The resulting particles have nearly neutral surfaces (−5.1 ± 2.3 mV, Supplementary Fig. 13), minimal cell toxicity (Supplementary Fig. 14) and minimal protein-adsorption (Supplementary Fig. 15). These features allow for the ultimate use of these CS-SPs in various biological systems.


Magneto-fluorescent core-shell supernanoparticles.

Chen O, Riedemann L, Etoc F, Herrmann H, Coppey M, Barch M, Farrar CT, Zhao J, Bruns OT, Wei H, Guo P, Cui J, Jensen R, Chen Y, Harris DK, Cordero JM, Wang Z, Jasanoff A, Fukumura D, Reimer R, Dahan M, Jain RK, Bawendi MG - Nat Commun (2014)

Silica-coated CS-SPsa, A representative TEM image of silica-coated CS-SPs (silica-CS-SPs) with a thin layer thickness of ~ 10.6 ± 0.7 nm. Scale bar is 200 nm. Insets show the histogram of the particle diameter distribution of silica-CS-SPs with an average diameter of 100 ± 12 nm (top right) and a zoomed-in TEM image of one silica-CS-SP (bottom right). Scale bar in the inset is 50 nm. b, An image of dark-field scanning TEM (STEM) and elemental line scan from a silica-CS-SP show that, while maintaining the core-shell superstructure, a thin layer of silica shell is uniformly deposited onto the CS-SP’s surface. Scale bar is 50 nm. c, HD diameter and relative photoluminescence (relat. PL) intensity of silica-CS-SPs as a function of storage time. d, Magnetic characterization (magnetization versus magnetic field at 300K) shows the superparamagnetism of silica-CS-SPs. e, Left, epi fluorescence image of silica-CS-SPs on a glass substrate. Right, a representative photoluminescence time trace of a single silica-CS-SP.
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Figure 3: Silica-coated CS-SPsa, A representative TEM image of silica-coated CS-SPs (silica-CS-SPs) with a thin layer thickness of ~ 10.6 ± 0.7 nm. Scale bar is 200 nm. Insets show the histogram of the particle diameter distribution of silica-CS-SPs with an average diameter of 100 ± 12 nm (top right) and a zoomed-in TEM image of one silica-CS-SP (bottom right). Scale bar in the inset is 50 nm. b, An image of dark-field scanning TEM (STEM) and elemental line scan from a silica-CS-SP show that, while maintaining the core-shell superstructure, a thin layer of silica shell is uniformly deposited onto the CS-SP’s surface. Scale bar is 50 nm. c, HD diameter and relative photoluminescence (relat. PL) intensity of silica-CS-SPs as a function of storage time. d, Magnetic characterization (magnetization versus magnetic field at 300K) shows the superparamagnetism of silica-CS-SPs. e, Left, epi fluorescence image of silica-CS-SPs on a glass substrate. Right, a representative photoluminescence time trace of a single silica-CS-SP.
Mentions: With their combination of both magnetism and fluorescence, CS-SPs have potential in various applications and technological devices. However, feasible applications, especially in biological systems, often require additional surface functionality, and this can be significantly hindered with CS-SPs that have a PVP polymer surface. To overcome this challenge and improve biocompatibility and colloidal stability, we encapsulate CS-SPs (~ 80 nm) with a thin silica shell through a sol-gel process38, 39. TEM characterization shows that each CS-SP is uniformly coated with a 10.6 ± 0.7 nm thick silica shell (Fig. 3a). STEM line scan, element mapping and 3D TEM tomography show that the core-shell superstructure is preserved (Fig. 3b, Supplementary Fig. 6 and Supplementary Movie 3). DLS measurements reveal that the HD diameter dramatically decreases from ~ 130 nm to ~ 100 nm, similar to the TEM-determined size of ~100 nm (Fig. 3a and Supplementary Fig. 7). The decrease in HD size implies a complete removal of the bulky PVP layer. Importantly, these silica-coated CS-SPs (silica-CS-SPs) display a high degree of colloidal stability. No measureable changes in both the PL intensity and HD size can be observed after 6-month at 4 °C (Fig. 3c). These silica-CS-SPs exhibit superparamagnetism at room temperature with a saturation magnetization of 15.2 emu g−1 (1.4 × 10−14 emu per particle) (Fig. 3d and Supplementary Fig. 8 and Supplementary Table 3). The decreased magnetization compared to that of free Fe3O4 MNPs (63.7 emu g−1, Supplementary Fig. 9) is due to non-magnetic components inside each silica-CS-SP (the QDs, the silica layer, and the organic ligands) with a mass percentage of 75.2% (Supplementary Fig. 10 and Supplementary Table 3). The PL QY of the silica-CS-SPs was measured to be ~12% using a 405 nm excitation light, comparable with that of the PVP-coated CS-SPs (Supplementary Fig. 11). The decreased QY compared to free QDs (PL QY of 94%) is in large part a result of the MNPs strongly absorbing this wavelength light. Under the illumination of a continuous wave laser at a power density of 22 W cm−2 for ~ 2800 second, silica-CS-SPs did not show evidence either of blinking or photo-bleaching (Fig. 3e), thus making them an ideal tool for single particle tracking. To demonstrate the silica-layer enabled surface functionality, methoxy-polyethylene-glycol silane (mPEG-silane, MW5000) was conjugated to the CS-SPs (Supplementary Fig. 12). The resulting particles have nearly neutral surfaces (−5.1 ± 2.3 mV, Supplementary Fig. 13), minimal cell toxicity (Supplementary Fig. 14) and minimal protein-adsorption (Supplementary Fig. 15). These features allow for the ultimate use of these CS-SPs in various biological systems.

Bottom Line: A thin layer of silica coating provides high colloidal stability and biocompatibility, and a versatile surface functionality.We demonstrate that after surface pegylation, these silica-coated magneto-fluorescent supernanoparticles can be magnetically manipulated inside living cells while being optically tracked.Moreover, our silica-coated magneto-fluorescent supernanoparticles can also serve as an in vivo multi-photon and magnetic resonance dual-modal imaging probe.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.

ABSTRACT
Magneto-fluorescent particles have been recognized as an emerging class of materials that exhibit great potential in advanced applications. However, synthesizing such magneto-fluorescent nanomaterials that simultaneously exhibit uniform and tunable sizes, high magnetic content loading, maximized fluorophore coverage at the surface and a versatile surface functionality has proven challenging. Here we report a simple approach for co-assembling magnetic nanoparticles with fluorescent quantum dots to form colloidal magneto-fluorescent supernanoparticles. Importantly, these supernanoparticles exhibit a superstructure consisting of a close-packed magnetic nanoparticle 'core', which is fully surrounded by a 'shell' of fluorescent quantum dots. A thin layer of silica coating provides high colloidal stability and biocompatibility, and a versatile surface functionality. We demonstrate that after surface pegylation, these silica-coated magneto-fluorescent supernanoparticles can be magnetically manipulated inside living cells while being optically tracked. Moreover, our silica-coated magneto-fluorescent supernanoparticles can also serve as an in vivo multi-photon and magnetic resonance dual-modal imaging probe.

Show MeSH
Related in: MedlinePlus