Versatile Synthesis Strategy for Carboxylic Acid−functionalized Upconverting Nanophosphors as Biological Labels

Abstract

Up-converting rare-earth nanophosphors (UCNPs) have great potential to revolutionize biological luminescent labels, but their use has been limited by difficulties in obtaining UCNPs that are biocompatible. To address this problem, we have developed a simple and versatile strategy for converting hydrophobic UCNPs into water-soluble and carboxylic acid-functionalized analogues by directly oxidizing oleic acid ligands with the Lemieux-von Rudloff reagent. This oxidation process has no obvious adverse effects on the morphologies, phases, compositions and luminescent capabilities of UCNPs. Furthermore, as revealed by Fourier transform infrared (FTIR) and NMR results, oleic acid ligands on the surface of UCNPs can be oxidized into azelaic acids (HOOC(CH2)7COOH), which results in the generation of free carboxylic acid groups on the surface. The presence of free carboxylic acid groups not only confers high solubility in water, but also allows further conjugation with biomolecules such as streptavidin. A highly sensitive DNA sensor based on such streptavidin-coupled UCNPs have been prepared, and the demonstrated results suggest that these biocompatible UCNPs have great superiority as luminescent labeling materials for biological applications.

White-light upconversion emission of lanthanide double-doped oxide nanoparticles via defect state luminescence of ZnO

“…The doping of Ln 3+ ions can convert the near-infrared (NIR) into visible light. The NIR excitation can penetrate the skin, which has potential biological applications, such as bioimaging and multifunctional biological probes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The white UCL has a broad range of emission wavelengths, including blue, green, and red emissions, generating a large library of spectral region that can be used for multiplexed biological labeling and encoding [16,17].…”

Upconversion fluorescence resonance energy transfer—a novel approach for sensitive detection of fluoroquinolones in water samples

“…The hexagonal phase NaLuF 4 is often synthesized in organic solvents under high temperature or by using suitable dopants. Gd 3+ was added to the system in order to increase the upconversion luminescence and for the reduction of particle size [36,42,44,47]. The shapes of the particles are highly influenced by the crystallographic phase of the initial seeds that have been formed during the nucleation process.…”

“…However, hydrophobic UCPs cannot be directly labeled by antibodies and used in the biology detection because of low solubility in water and unfavorable surface properties, it has to be converted into biocompatible one using appropriate functional groups (-COOH, -NH 2 , -SH) through exchange ligand process or UCPs-SiO 2 core-shell structure [24,[36][37][38]. At present, the method of encapsulation with SiO 2 was widely used as a surface functionalization of hydrophobic UCPs, but this procedure was suffered from high cost, complicated procedures and difficulty in controlling the thickness and uniformity of the SiO 2 layer.…”

“…In the present work, a highly monodisperse and uniform UCPs were synthesized, and the surface was modified into biocompatible by adopting the poly(acrylic acid) (PAA)-based ligand exchange strategies [36,39]. The UCPs were made as an energy donor after their surface functionalization with a group-specific Mab against FQs.…”

Monodisperse Water-Stable Sio2- Coated Fluoride Upconversion Nanoparticles with Tunable Shell Thickness

“…To solve this problem, the surface chemistry of as-prepared UCNPs have to be designed to grant both a stable aqueous colloidal dispersion and the ability to conjugate biomolecules. Several approaches has been attempted toward this regard, including SiO 2 coating, wrapping by small molecular surfactant, amphiphilic polymer, oxidizing oleic acid ligands with the Lemieuxvon Rudolf reagent, and ligand exchange [11,[15][16][17][18][19][20][21][22][23][24][25]. In particular, SiO 2 -coating are of particular interest, due to its high biocompatibility, easy surface modifi cation through silicon-enriched chemistry, and easy control of interparticle interactions [26][27][28][29].…”