Rare-earth Upconversion Nanophosphors Research Articles

Anticounterfeiting and Security Applications of Rare-Earth Upconversion Nanophosphors

Anticounterfeiting and Security Applications of Rare-Earth Upconversion Nanophosphors

Thermo-responsive enhanced emission rare-earth upconversion nanophosphors based on NaLuF4:Yb3 +,Er3 +functionalized with PNIPAM for cell imaging

The densities of state and optical properties of matrix materials were studied with the help of first-principles calculations. It is found that the absorption and reflectance of the NaGdF4 system in the infrared region were comparatively low. Such low values were beneficial to the reduction of the loss of excitation light. Furthermore, Er3+ and Yb3+ co-doped NaREF4 (RE: Gd, Lu, Y) were prepared by a simple hydrothermal method, which exhibited a regularly shaped hexagonal microrods. Under the excitation of 808 nm, 980 nm, 1064 nm and 1550 nm, three emission peaks were all observed at 521, 540 and 655 nm for these samples, and NaGdF4: Yb/Er has the highest fluorescence intensity among the three samples. Calculated and experimental results demonstrated that NaGdF4 is more suitable than the two other materials as a substrate for UC luminescence.

Novel Upconversion Fluorescent Probe for Schistosoma japonicum Cercariae Imaging

Schistosomiasis has influence on people’s security and daily life significantly, while cercarial stage of the schistosome life-cycle is the only infectious period. To detect cercarial efficiently, we synthesized rare-earth upconversion nanophosphors UCs-Ni loaded with niclosamide. The fluorescenceof UCs-Ni was demonstrated by the fluorescence emission spectra. The cell imaging test illustrated that UCs-Ni was biocompatible, cell-permeable and suitable for cercariae imaging. When it has been utilized for cercariae imaging, we found that the UCs-Ni could penetrate into cercariae.

One-step synthesis of water-dispersible hydroxyl-functionalized NaYF4:Yb/Er upconversion nanoparticles

Rare-earth upconversion nanophosphors (UCNPs) with high water-dispersibility and surface functional groups are promising for bioimaging. In this paper, we reported a facile strategy for one-step synthesis of water-dispersible hydroxyl-functionalized NaYF4:Yb/Er UCNPs based on the solvothermal technique by using ricinoleic acid as ligand. TEM and XRD characterizations indicate that the synthesized UCNPs possess hexagonal phase structure and spherical shape with a mean diameter of 20nm. The UCNPs show excellent water-dispersibility and strong upconversion luminescence. Moreover, the presence of hydroxyl groups on the surface of NaYF4:Yb/Er allows for further modification as confirmed by the successful reaction with dodecanoyl chloride. Our strategy opens up opportunities to make full use of water-dispersible UCNPs in various applications because of their facile availability, cost-effective productivity and favorable surface functionality.

A Cyanine-Modified Nanosystem forin VivoUpconversion Luminescence Bioimaging of Methylmercury

Methylmercury (MeHg(+)) is a strong liposoluble ion, which can be accumulated in the organs of animals and can cause prenatal nervous system and visceral damage. Therefore, the efficient and sensitive monitoring of MeHg(+) in organisms is of great importance. Upconversion luminescence (UCL) detection based on rare-earth upconversion nanophosphors (UCNPs) as probes has been proved to exhibit a large anti-Stokes shift, no autofluorescence from biological samples, a remarkably deep penetration depth, and no photobleaching. In this study, a hydrophobic heptamethine cyanine dye (hCy7) modified by two long alkyl moieties and amphiphilic polymer (P-PEG)-modified nanophosphors (hCy7-UCNPs) was fabricated as a highly sensitive water-soluble probe for UCL monitoring and bioimaging of MeHg(+). Further application of hCy7-UCNPs for sensing MeHg(+) was confirmed by an optical titration experiment and upconversion luminescence live cell imaging. Using the ratiometric upconversion luminescence as a detection signal, which provides a built-in correction for environmental effects, the detection limit of MeHg(+) for this nanosystem was as low as 0.18 ppb. Importantly, the hCy7-UCNPs nanosystem was shown to be capable of monitoring MeHg(+)ex vivo and in vivo by upconversion luminescence bioimaging.

ChemInform Abstract: Upconversion Nanophosphors for Small‐Animal Imaging

AbstractReview: 276 refs.

Upconversion nanophosphors for small-animal imaging

Rare-earth upconversion nanophosphors (UCNPs), when excited by continuous-wave near-infrared light, exhibit a unique narrow photoluminescence with higher energy. Such special upconversion luminescence makes UCNPs promising as bioimaging probes with attractive features, such as no auto-fluorescence from biological samples and a large penetration depth. As a result, UCNPs have emerged as novel imaging agents for small animals. In this critical review, recent reports regarding the synthesis of water-soluble UCNPs and their surface modification and bioconjugation chemistry are summarized. The applications of UCNPs for small-animal imaging, including tumor-targeted imaging, lymphatic imaging, vascular imaging and cell tracking are reviewed in detail. The exploration of UCNPs as multifunctional nanoscale carriers for integrated imaging and therapy is also presented. The biodistribution and toxicology of UCNPs are further described. Finally, we discuss the challenges and opportunities in the development of UCNP-based nanoplatforms for small-animal imaging (276 references).

High-quality water-soluble and surface-functionalized upconversion nanocrystals as luminescent probes for bioimaging

Rare-earth upconversion nanophosphors (UCNPs) have great potential to become excellent biological luminescent labels for fluorescence bioimaging. However, it is still difficult to directly synthesize high-quality water-soluble UCNPs bearing appropriate functional groups using a one-step synthetic strategy. Herein, we report a one-step synthetic strategy for high-quality water-soluble and surface-functionalized UCNPs using a hydrothermal reaction assisted by binary cooperative ligands (HR-BCL). In this system, 6-aminohexanoic acid and oleate were introduced to control nuclear generation and crystal growth of small nanoparticles. The UCNPs synthesized here showed high crystalline and intense upconversion luminescence emission. Fourier-transform infrared and nuclear magnetic resonance spectroscopy indicated that 6-aminohexanoic acid and oleate cooperate as surface ligands to co-control the surface of UCNPs. Thus, the water-solubility of the as-prepared UCNPs can be tuned by changing the molar ratio of 6-aminohexanoic acid to oleate. The AA-modified UCNPs provided a free amine content of (6.0 ± 0.2) × 10−5 mol/g, which renders them dispersible in aqueous solution and allows further conjugation with folic acid (FA) for targeted bioimaging. Furthermore, the amine-functionalized UCNPs show intense near-infrared upconversion luminescence and were successfully applied in the lymphatic capillary bioimaging of small animals with a high signal-to-noise ratio, suggesting that these surface-functionalized UCNPs are promising candidates for luminescent biolabels.

Long-term in vivo biodistribution imaging and toxicity of polyacrylic acid-coated upconversion nanophosphors

Rare-earth upconversion nanophosphors (UCNPs) have become one of the most promising classes of luminescent materials for bioimaging. However, there remain numerous unresolved issues with respect to the understanding of how these nanophosphors interact with biological systems and the environment. Herein, we report polyacrylic acid (PAA)-coated near-infrared to near-infrared (NIR-to-NIR) upconversion nanophosphors NaYF 4:Yb,Tm (PAA-UCNPs) as luminescence probes for long-term in vivo distribution and toxicity studies. Biodistribution results determined that PAA-UCNPs uptake and retention took place primarily in the liver and the spleen and that most of the PAA-UCNPs were excreted from the body of mice in a very slow manner. Body weight data of the mice indicated that mice intravenously injected with 15 mg/kg of PAA-UCNPs survived for 115 days without any apparent adverse effects to their health. In addition, histological, hematological and biochemical analysis were used to further quantify the potential toxicity of PAA-UCNPs, and results indicated that there was no overt toxicity of PAA-UCNPs in mice at long exposure times (up to 115 days). The study suggests that PAA-UNCPs can potentially be used for long-term targeted imaging and therapy studies in vivo.

Water-soluble NaYF4:Yb/Er upconversion nanophosphors: Synthesis, characteristics and application in bioimaging

This work describes the water-soluble NaYF 4 :Yb/Er, by replacing oleic acid with citrate to surface, can exhibit very bright luminescence in the effective detection of cancer (HeLa) cells. Water-soluble and citrate (cit) coated rare-earth upconversion nanophosphors (UCNPs) were prepared by an efficient surface ligand exchange of the oleic acid capped hydrophobic UCNPs in diethylene glycol (DEG) at high temperature. The successful surface ligand exchange of the UCNPs with citrate was confirmed by Fourier-transform infrared (FTIR) spectroscopy. Further characterizations such as TEM and XRD showed that the ligand exchange reaction had no obvious influence on chemical properties of UCNPs, such as morphology and crystallization. Furthermore, bright UC luminescence was observed when UCNPs-labeled cells were excited with 980nm near-infrared (NIR) light proving that Cit-UCNPs can be used as non-specific labels for imaging HeLa cells. These results indicate that the Cit-UCNPs are a promising candidate for use as bioimaging probes.

A versatile fabrication of upconversion nanophosphors with functional-surface tunable ligands

Rare earth upconversion nanophosphors (UCNPs) have been recognized as a promising new class of biological luminescent labels for fluorescence imaging. However, little work has been reported on the successful application of UCNPs in fluorescence imaging so far. The major problem with UCNPs arises from the difficulties in obtaining water-soluble UCNPs bearing appropriate surface functional groups. To solve this problem, herein we report a general procedure for the one-pot preparation of surface-functionalized UCNPs by a modified polyol route assisted by difunctional ligands containing a carboxyl group, such as 11-aminoundecanoic acid (ADA), poly(ethylene glycol)bis(carboxymethyl)ether (PEGBA) and folic acid (FA). The success of this one-pot method was confirmed by FT-IR and 1H NMR spectroscopy. Due to the amino and carboxyl groups pointing outward, both amino-functionlized UCNPs (UCNPs-ADA) and carboxyl-functionlized UCNPs (UCNPs-PEGBA) are particularly suitable for coupling reactions with biological molecules and are potential candidates for bioimaging labels. By means of laser scanning upconversion luminescence microscopy, FA-functionlized UCNPs (UCNPs-FA) have been demonstrated to be effective in targeting folate-receptors overexpressing cancer cell lines. It is possible to design other surface-functionalized UCNPs by changing other bifunctional ligands with a carboxyl group. This strategy is general and facile for frabricating surface-functionalized UCNPs to potentially be used as bioimaging agents.