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Facile Synthesis of Amine-Functionalized Eu 3+ -Doped La(OH) 3 Nanophosphors for Bioimaging

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ABSTRACT

Here, we report a straightforward synthesis process to produce colloidal Eu3+-activated nanophosphors (NPs) for use as bioimaging probes. In this procedure, poly(ethylene glycol) serves as a high-boiling point solvent allowing for nanoscale particle formation as well as a convenient medium for solvent exchange and subsequent surface modification. The La(OH)3:Eu3+ NPs produced by this process were ~3.5 nm in diameter as determined by transmission electron microscopy. The NP surface was coated with aminopropyltriethoxysilane to provide chemical functionality for attachment of biological ligands, improve chemical stability and prevent surface quenching of luminescent centers. Photoluminescence spectroscopy of the NPs displayed emission peaks at 597 and 615 nm (λex = 280 nm). The red emission, due to 5D0 → 7F1 and 5D0 → 7F2 transitions, was linear with concentration as observed by imaging with a conventional bioimaging system. To demonstrate the feasibility of these NPs to serve as optical probes in biological applications, an in vitro experiment was performed with HeLa cells. NP emission was observed in the cells by fluorescence microscopy. In addition, the NPs displayed no cytotoxicity over the course of a 48-h MTT cell viability assay. These results suggest that La(OH)3:Eu3+ NPs possess the potential to serve as a luminescent bioimaging probe.

No MeSH data available.


XPS survey scan of a as-synthesized and b APTES-coated NPs.
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Figure 3: XPS survey scan of a as-synthesized and b APTES-coated NPs.

Mentions: To confirm the NP composition and evaluate the surface modification process, both as-synthesized and APTES-coated NPs were characterized by XPS. The survey scan obtained from the as-synthesized NPs (Figure 3a) confirms the primary composition of lanthanum and oxygen with main peaks of La 3d5 and O 1s centered at ca. 835.2 and 531.1 eV, respectively. In addition, the presence of physically adsorbed PEG in these samples likely contributes to the prominent C 1 s peak. The low concentration of the Eu3+ dopant (<5 mol%) is below the detection limit of this technique. Confirmation of the dopant in NPs is described in the following section. The XPS survey scan of the APTES-coated NPs (Figure 3b) displays peaks characteristic of the amine-bearing silane in addition to the NP matrix. Main peaks of Si 2 s and N 1s at binding energies of 152.2 and 400.7 eV, respectively, confirm the surface functionalization of NPs. An additional peak at 458.3 eV was identified as titanium (Ti 2p3), which was also incorporated in the coating from the Ti(OPr)4 catalyst [32]. The presence of this siloxane bound coating improves the chemical stability and protects the Eu3+ luminescent centers that may be located at or near the surface of the NP from quenching by water. Furthermore, the terminal amine group serves as a convenient linking chemistry for bioconjugation [33,34], which is necessary for biological applications.


Facile Synthesis of Amine-Functionalized Eu 3+ -Doped La(OH) 3 Nanophosphors for Bioimaging
XPS survey scan of a as-synthesized and b APTES-coated NPs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211300&req=5

Figure 3: XPS survey scan of a as-synthesized and b APTES-coated NPs.
Mentions: To confirm the NP composition and evaluate the surface modification process, both as-synthesized and APTES-coated NPs were characterized by XPS. The survey scan obtained from the as-synthesized NPs (Figure 3a) confirms the primary composition of lanthanum and oxygen with main peaks of La 3d5 and O 1s centered at ca. 835.2 and 531.1 eV, respectively. In addition, the presence of physically adsorbed PEG in these samples likely contributes to the prominent C 1 s peak. The low concentration of the Eu3+ dopant (<5 mol%) is below the detection limit of this technique. Confirmation of the dopant in NPs is described in the following section. The XPS survey scan of the APTES-coated NPs (Figure 3b) displays peaks characteristic of the amine-bearing silane in addition to the NP matrix. Main peaks of Si 2 s and N 1s at binding energies of 152.2 and 400.7 eV, respectively, confirm the surface functionalization of NPs. An additional peak at 458.3 eV was identified as titanium (Ti 2p3), which was also incorporated in the coating from the Ti(OPr)4 catalyst [32]. The presence of this siloxane bound coating improves the chemical stability and protects the Eu3+ luminescent centers that may be located at or near the surface of the NP from quenching by water. Furthermore, the terminal amine group serves as a convenient linking chemistry for bioconjugation [33,34], which is necessary for biological applications.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Here, we report a straightforward synthesis process to produce colloidal Eu3+-activated nanophosphors (NPs) for use as bioimaging probes. In this procedure, poly(ethylene glycol) serves as a high-boiling point solvent allowing for nanoscale particle formation as well as a convenient medium for solvent exchange and subsequent surface modification. The La(OH)3:Eu3+ NPs produced by this process were ~3.5 nm in diameter as determined by transmission electron microscopy. The NP surface was coated with aminopropyltriethoxysilane to provide chemical functionality for attachment of biological ligands, improve chemical stability and prevent surface quenching of luminescent centers. Photoluminescence spectroscopy of the NPs displayed emission peaks at 597 and 615 nm (&lambda;ex = 280 nm). The red emission, due to 5D0 &rarr; 7F1 and 5D0 &rarr; 7F2 transitions, was linear with concentration as observed by imaging with a conventional bioimaging system. To demonstrate the feasibility of these NPs to serve as optical probes in biological applications, an in vitro experiment was performed with HeLa cells. NP emission was observed in the cells by fluorescence microscopy. In addition, the NPs displayed no cytotoxicity over the course of a 48-h MTT cell viability assay. These results suggest that La(OH)3:Eu3+ NPs possess the potential to serve as a luminescent bioimaging probe.

No MeSH data available.