Clean and Flexible Modification Strategy for Carboxyl/Aldehyde‐Functionalized Upconversion Nanoparticles and Their Optical Applications

Abstract

Rare‐earth upconversion nanoparticles (UCNPs) exhibit great potential in luminescent biolabels and other multifunctional probes; however, their applications are limited by their low water solubility and the lack of binding groups. To address these problems, a clean and flexible strategy to modify hydrophobic monodisperse UCNPs into hydrophilic ones that are capped with functional groups is developed. The modification process is implemented by direct oxidation of oleic acid ligands with ozone under specific conditions, where the oleic acid (OA) ligands on the surface of the UCNPs can be converted into azelaic acid ligands (HOOC(CH2)7COOH) or azelaic aldehyde HOOC(CH2)7CHO, as is revealed by Fourier‐transform infrared (FTIR) and nuclear magnetic resonance (NMR) measurements. This oxidation process has no significant side‐effects on the morphology, phase, composition, or luminescent properties of the UCNPs. Free carboxylic acid groups on the surface endow the UCNPs with good water solubility, while aldehyde groups at the surface provide binding sites for amino‐containing molecules via Schiff‐base condensation, such as 2‐(4‐aminophenylethylyl)‐5‐methoxy‐2‐(2‐pyridyl)thiazole (MPTEA) and 2‐aminoethanethiol hydrochloride (NH2CH2CH2SH·HCl, HEMA). A Ce4+ sensor is constructed based on the dual‐emission arising from the different spectral responses of MPTEA and the UCNPs. Facilitated by the covalent linkage between the terminal aldehyde group on the UCNPs and the amino group in HEMA, a hybrid structure of UCNPs and Au NPs is fabricated. The effective coupling between the aldehyde group and the amino group suggests that these functionalized UCNPs have potential in combining other functional units for simultaneous biolabeling, or other optical applications.

Up-Conversion Nanoparticle Assembled Mesoporous Silica Composites: Synthesis, Plasmon-Enhanced Luminescence, and Near-Infrared Light Triggered Drug Release

“…The population process for the three emissions has been reported a lot following the procedure below: 4 I 15/2 → 4 I 11/2 → 4 F 7/2 → 2 H 11/2 , 4 S 3/2 for the green emission and 4 I 15/2 → 4 I 11/2 → 4 I 13/2 → 4 F 9/2 for the red emission − (Figure D). It is well-known that attachment of the noble metal shell or nanostructures on the UC materials can affect the UC luminescence behaviors. , In this case, although the enhancement is not obvious in the UC spectra, through calculating the integrated peak area, we do find out that the emission intensities of MCM-41-Gd@Au and MCM-48-Gd@Au are increased compared to those of MCM-41-Gd and MCM-48-Gd samples. The enhancement factors for the green emission (520–560 nm), red emission (640–670 nm), and total emission intensities (520–670 nm) are calculated in Figure C.…”

A User-Friendly Method for Synthesizing High-QualityNaYF4:Yb,Er(Tm) Nanocrystals in Liquid Paraffin

“…In the current synthesis, moreover, the asprepared NCs possessed a pure β-phase (Figure 1(e)), leading to the strong up-conversion fluorescence [37]. Overall, the highly crystalline structure, narrow size distribution, and strong up-conversion fluorescence of the products indicated that the NaYF 4 :Yb,Er NCs synthesized in liquid paraffin possessed a high quality, which was comparable to the corresponding NCs synthesized in the conventional solvent of octadecene (ODE) [2,3,38].…”

Surface Modification and Bioconjugation of Upconversion Nanoparticles

“…By contrast, Yan and coworkers reported the oxidation of OA into the azelaic aldehyde or azelaic acid through ozonolysis on the surface of NaYF 4 :Yb/Er NPs [55]. In this work, the hydrophobic OA-capped UCNPs were converted into amphiphilic ones by ozonolysis, combined with a subsequent oxidation or reduction treatment (Fig.…”