Er Upconversion Nanophosphors Research Articles

Facile synthesis of multicolor tunable ultrasmall LiYF4:Yb,Tm,Er/LiGdF4 core/shell upconversion nanophosphors with sub-10 nm size

Sub-10 nm-sized LiYF4:Yb,Tm/Er upconversion nanophosphors (UCNPs) and multicolor-emitting LiYF4:Yb,Tm,Er/LiGdF4 core/shell (C/S) UCNPs were facilely synthesized by using rare earth-oleate (RE(oleate)3) precursors. The size of LiYF4:Yb,Tm and LiYF4:Yb,Er UCNPs with single tetragonal phase was controlled in the range of 3.2–9.6 nm and 3.0–9.0 nm, respectivley, by varying reaction temperature from 230 to 320 °C under the use of RE(oleate)3 precursors. The sub-10 nm-sized LiYF4:Yb(25%),Tm(0.5%)/LiGdF4 (9.7 nm) and LiYF4:Yb(18%),Er(2%)/LiGdF4 (9.5 nm) C/S UCNPs were successfully synthesized from ultrasmall LiYF4-based UCNP cores smaller than 5 nm in size. The blue- and green-emitting sub-10 nm-sized LiYF4:Yb,Tm/LiGdF4 and LiYF4:Yb,Er/LiGdF4 C/S UCNPs exhibited 566 and 48,245 times higher upconversion luminescence intensities than their core counterparts, respectivley, under excitation with 980 nm near infrared light. In addition, multicolor tunable sub-10 nm-sized LiYF4:Yb,Tm,Er/LiGdF4 C/S UCNPs were synthesized and they emitted bright blue, sky blue, aquamarine, and green light by varying dopant composition (Tm and Er) and concentration.

Highly Bright and Photostable Li(Gd,Y)F4:Yb,Er/LiGdF4Core/Shell Upconversion Nanophosphors for Bioimaging Applications

Intense green-emitting Li(Gd,Y)F4:Yb,Er/LiGdF4 core/shell (C/S) upconversion nanophosphors (UCNPs) with a tetragonal bipyramidal morphology are synthesized. The morphology and UC luminescence of the Li(Gd,Y)F4:Yb,Er UCNPs are significantly affected by the Li precursors, and bright UC green-emitting Li(Gd,Y)F4:Yb,Er UCNPs with a tetragonal bipyramidal shape, i.e., UC tetragonal bipyramids (UCTBs), are synthesized using LiOH·H2O as a Li precursor. A LiGdF4 shell is grown on the Li(Gd,Y)F4:Yb,Er UCTBs, and the C/S UCNPs exhibit 4.7 times higher luminescence intensity than core UCTBs. The C/S UCNPs show a high absolute UC quantum yield of 4.6% under excitation with 980 nm near infrared (NIR) light, and the UC luminescence from the C/S UCNPs is stable under continuous irradiation with the 980 nm NIR laser for 1 h. The hydrophobic surfaces of the as-synthesized C/S UCNPs are modified to hydrophilic surfaces by using poly(acrylic acid) (PAA) for bioimaging applications. They are applied to human cervical adenocarcinoma (HeLa) cell imaging and SK-MEL-2 melanoma cell imaging and in vivo imaging, including subcutaneous and intramuscular imaging, and UC luminescence images with high signal-to-noise ratio are obtained. Furthermore, sentinel-lymph-node imaging is successfully conducted with the PAA-capped Li(Gd,Y)F4:Yb,Er/LiGdF4 C/S UCNPs under illumination with NIR light.

Upconversion Nanophosphor: An Efficient Phosphopeptides-Recognizing Matrix and Luminescence Resonance Energy Transfer Donor for Robust Detection of Protein Kinase Activity

Protein kinases play important regulatory roles in intracellular signal transduction pathways. The aberrant activities of protein kinases are closely associated with the development of various diseases, which necessitates the development of practical and sensitive assays for monitoring protein kinase activities as well as for screening of potential kinase-targeted drugs. We demonstrate here a robust luminescence resonance energy transfer (LRET)-based protein kinase assay by using NaYF4:Yb,Er, one of the most efficient upconversion nanophosphors (UCNPs), as an autofluorescence-free LRET donor and a tetramethylrhodamine (TAMRA)-labeled substrate peptide as the acceptor. Fascinatingly, besides acting as the LRET donor, NaYF4:Yb,Er UCNPs also serve as the phosphopeptide-recognizing matrix because the intrinsic rare earth ions of UCNPs can specifically capture the fluorescent phosphopeptides catalyzed by protein kinases over the unphosphorylated ones. Therefore, a sensitive and generic protein kinase assay is developed in an extremely simple mix-and-read format without any requirement of surface modification, substrate immobilization, separation, or washing steps, showing great potential in protein kinases-related clinical diagnosis and drug discovery. To the best of our knowledge, this is the first report by use of rare earth-doped UCNPs as both the phospho-recognizing and signal reporting elements for protein kinase analysis.

Multi-Functional Magnetic Photoluminescent Photocatalytic Polystyrene-Based Micro- and Nano-Fibers Obtained by Electrospinning

This work reports on the implementation of electrospinning (ES) as a facile route to encapsulate nano-engineered materials in a polystyrene (PS) matrix. We applied ES to co-encapsulate two kinds of nanoparticles, i.e., upconversion nanophosphors (UCNPs) and superparamagnetic iron oxide nanoparticles (SPIONs), in polystyrene (PS)-based micro- and nano-fibers (PSFs). This approach made it possible to integrate near-infrared (NIR) light-sensitive 500-nm β-NaYF4:Yb, Er UCNPs with 10-nm γ-Fe2O3 SPIONs in PS fibers. During the ES process, PSFs were additionally loaded with a well-established singlet oxygen (1∆g) photosensitizer, rose bengal (RB). The thus obtained PSFs revealed the promising features of prospective multi-functional magnetic photoluminescent photocatalytic nano-constructs.

Surface modification of hydrophobic NaYF4:Yb,Er upconversion nanophosphors and their applications for immunoassay

β-NaYF4:Yb,Er upconversion nanophosphor (UCNP) is known as one of the most efficient NIR-to-visible upconversion materials, which shows great potential in bioanalytical chemistry and bioimaging. However, its applications are greatly limited due to its low water dispersibility and thus poor biocompatibility. In this paper, poly(acrylic acid) (PAA)-based ligand exchange strategies are carried out to modify oleic acid-capped hydrophobic β-NaYF4:Yb,Er UCNPs into hydrophilic ones. After efficient surface modification, the presence of free carboxylic acid groups on the surfaces of UCNPs results in high solubility in water, and also allows further conjugation with NH2-containing biomolecules. Facilitated by the covalent linkage between the-COOH groups on UCNPs surfaces and-NH2 groups in antigen/antibody, a sensitive immunosensor is constructed by using PAA-functionalized β-NaYF4:Yb,Er UCNPs as biolabels. Through monitoring the upconversion fluorescence intensity or fluorescent imaging of the final immunocomplexes, high sensitivity is achieved for the proposed immunoassay and as low as 0.1 ng/mL goat anti-human immunoglobulin G (IgG) can be detected, which suggests that PAA-modified UCNPs may serve as an ideal candidate for use as bioanalysis and bioimaging probes.

Controllable synthesis of NaYF(4) : Yb,Er upconversion nanophosphors and their application to in vivo imaging of Caenorhabditis elegans.

β-NaYF(4) : Yb,Er upconversion nanoparticles (UCNPs) can emit bright green fluorescence under near-infrared (NIR) light excitation which is safe to the body and can penetrate deeply into tissues. The application of UCNPs in biolabeling and imaging has received great attention recently. In this work, β-NaYF(4) : Yb,Er UCNPs with an average size of 35 nm, uniformly spherical shape, and surface modified with amino groups were synthesized by a one-step green solvothermal approach through the use of room-temperature ionic liquids as the reactant, co-solvent and template. The as-prepared UCNPs were introduced into Caenorhabditis elegans (C. elegans) to achieve successful in vivo imaging. We found that longer incubation time, higher UCNP concentration and smaller UCNP size can make the in vivo fluorescence of C. elegans much brighter and more continuous along their body. The worms have no apparent selectivity on ingestion of the UCNPs capped with different capping ligands while having similar size and shape. The next generation of worms did not show fluorescence under excitation. In addition, low toxicity of the nanoparticles was demonstrated by investigating the survival rates of the worms in the presence of the UCNPs. Our work demonstrates the potential application of the UCNPs in studying the biological behavior of organisms, and lays the foundation for further development of the UCNPs in the detection and diagnosis of diseases.

An investigation of the thermal sensitivity and stability of the β-NaYF4:Yb,Er upconversion nanophosphors

The upconversion luminescence (UCL) of the hexagonal (β)-phase NaYF4:Yb,Er nanophosphors as a function of temperature (300–450 K) was examined under 978 nm light excitation. The thermal sensitivity was evaluated based on the UCL intensity ratio between H211/2–I415/2 and S43/2–I415/2 transitions (RHS). Excitation power, particle sizes (37, 65, and 140 nm), ion doping concentrations, and with and without silica coating were studied. It was found that RHS is only dependent on temperature at the low excitation power, and has no direct relation with the particle size and surface effects. Silica coating was found to enhance the thermal stability significantly without altering the thermal sensitivity.

The Hidden Effects of Particle Shape and Criteria for Evaluating the Upconversion Luminescence of the Lanthanide Doped Nanophosphors

The dependences of upconversion luminescence (UCL) on the particle size, shape, and inorganic−ligand interface of the hexagonal (β)-phase NaYF4:Yb,Er upconversion nanophosphors (β-UCNPs) were studi...

Uniform YF3:Yb,Er up-conversion nanophosphors of various morphologies synthesized in polyol media through an ionic liquid

We describe a facile procedure for the synthesis at low temperature (120 °C) of water-dispersible uniform YF3:Yb,Er up-conversion nanophosphors of various morphologies (rhombic and spheroidal) by homogeneous precipitation in polyol solutions containing different lanthanide salts and an ionic liquid (1-butyl, 2-methylimidazolium tetrafluoroborate) as fluoride source. It is shown that the shape of the obtained nanoparticles is mainly determined by the nature of both, the polyol and the lanthanide precursors, which also affects to their colloidal stability in water suspensions. These morphological differences are explained on the basis of a different mechanism of particle formation. The efficiency of the up-conversion processes in the synthesized rhombic and spheroidal nanoparticles is also comparatively analyzed and the observed differences are justified on the basis of the different impurities incorporated to the nanophosphors during their synthesis process.

A single-step synthesis and the kinetic mechanism for monodisperse and hexagonal-phaseNaYF4:Yb, Er upconversion nanophosphors

A single-step synthesis for monodisperse and hexagonal-phase (β)NaYF4:Yb, Er upconversion nanophosphors (UCNPs) with a consistent hexagonalprism shape in the size range from 18 to 200 nm was achieved. The kineticmechanisms for the particle phase transition and growth were examined. Theβ-UCNPs were obtained via co-thermolysis of trifluoroacetate precursors in octadecene(ODE) with combined ligands of oleic acid (OA) and trioctylphosphine (TOP). Theexperimental results showed that the combined OA–TOP ligand was crucial for changingthe surface energy and controlling the particle shape over a broad size range. It wasfound that the particle sizes could be controlled by varying the molar ratios ofNa(CF3COO)/Re(CF3COO)3 (Re = Y, Yb, andEr). A high Na/Re ratio accelerated the cubic-phase transition and promoted the growth of smallerβ-UCNPs. Theformation of β-UCNPs was classified into kinetic and diffusion controlled stages, depending on the reactiontemperature and the dominant crystalline phases formed in each stage. In stage I, 250–310 °C, NaF generation wasthe limiting step and α-UCNPs were formed via a ‘burst of nucleation’. In stage II, above310 °C,the α-UCNPs formed were re-dissolved and the growth ofβ-UCNPs was a diffusion controlled process governed by the Gibbs–Thompsoneffect. A quasi-steady-state species assumption for NaF and a chemical potentialequilibrium in the solution were introduced to explain the particle size dependence onNa/Re ratios. The study of UC luminescence showed that the UC intensity was proportional to the sizes ofthe β-UCNPs.

Biofunctionalization, cytotoxicity, and cell uptake of lanthanide doped hydrophobically ligated NaYF4 upconversion nanophosphors

Surface biofunctionalization of the hydrophobic lanthanide ion doped hexagonal phase NaYF4:Yb,Er upconversion nanophosphors (UCNPs) was achieved by introducing amino and carboxyl groups, respectively. Amino groups were added by using the 3-aminopropyltrimethoxysilane reaction after a thin layer of SiO2 coating. The carboxyl groups on surface were added directly by coating modified amphiphilic polyacrylic acid polymer. Experimental studies of cytotoxicity and cell uptake of UCNPs were conducted. The cytotoxicity analysis of the functionalized UCNPs was conducted by methylthiazol tetrazolium assays. Cell uptake was accomplished by incubating the UCNPs with human osteosarcoma cells and proved by transmission electron microscopy. The results showed that the functionalized UCNPs had very low toxicity compared with the control group, while UCNPs taken into the cells indicated that they had very high biocompatibility. The imaging of UCNPs, which were incubated with AB12 mouse mesothelioma cells and excited by 1 W 980 nm light, showed individual particles with visible light emission. These results exhibited promising applications of functionalized UCNPs in cell imaging and photodynamic therapy.