Lanthanide-doped Upconversion Nanoparticles Research Articles

Shining a light on upconversion

By using lanthanide-doped upconversion nanoparticles, fibre-optic sensors can display sensitivities several orders of magnitude greater than those of existing fluorescent techniques.

An Exceptionally Simple Strategy for DNA-Functionalized Up-Conversion Nanoparticles as Biocompatible Agents for Nanoassembly, DNA Delivery, and Imaging

Lanthanide-doped up-conversion nanoparticles (UCNPs) have shown promise in biomedical applications. However, as the UCNPs are normally capped with hydrophobic ligands, it remains challenging to prepare biocompatible UCNPs with specific molecular recognition capabilities. We herein report an exceptionally simple strategy to prepare uniform DNA-modified UCNPs as versatile bioprobes. The approach can directly convert as-prepared hydrophobic UCNPs into water-soluble DNA-UCNPs without any chemical modification of UCNPs or oligonucleotides. Furthermore, DNA molecules on the DNA-UCNPs retain their biorecognition ability, allowing programmable assembly of hybrid nanostructures. More importantly, we show that these DNA-UCNPs are capable of crossing cell membranes without the need of transfection agents, and their use as agents for bioimaging and DNA delivery are also demonstrated. Finally, DNA aptamer-conjugated UCNPs can be readily used for targeted imaging of cancer cells.

Multifunctional polyoxometalates-modified upconversion nanoparticles: integration of electrochromic devices and antioxidants detection

We report a novel design, based on a combination of lanthanide-doped upconversion nanoparticles and polyoxometalates, for electrically controlled fluorescence switches and sensitive detection of antioxidants in aqueous solution.

The Effect of Surface Coating on Energy Migration-Mediated Upconversion

Lanthanide-doped upconversion nanoparticles have been the focus of a growing body of investigation because of their promising applications ranging from data storage to biological imaging and drug delivery. Here we present the rational design, synthesis, and characterization of a new class of core-shell upconversion nanoparticles displaying unprecedented optical properties. Specifically, we show that the epitaxial growth of an optically inert NaYF(4) layer around a lanthanide-doped NaGdF(4)@NaGdF(4) core-shell nanoparticle effectively prevents surface quenching of excitation energy. At room temperature, the energy migrates over Gd sublattices and is adequately trapped by the activator ions embedded in host lattices. Importantly, the NaYF(4) shell-coating strategy gives access to tunable upconversion emissions from a variety of activators (Dy(3+), Sm(3+), Tb(3+), and Eu(3+)) doped at very low concentrations (down to 1 mol %). Our mechanistic investigations make possible, for the first time, the realization of efficient emissions from Tb(3+) and Eu(3+) activators that are doped homogeneously with Yb(3+)/Tm(3+) ions. The advances on these luminescent nanomaterials offer exciting opportunities for important biological and energy applications.

NIR‐Triggered Release of Caged Nitric Oxide using Upconverting Nanostructured Materials

Lanthanide-doped upconversion nanoparticles (UCNPs) mediate nitric oxide uncaging from Roussin's black salt anion Fe4S3(NO)7− using NIR light from a simple diode laser operating continuously at 980 nm. This result offers a new paradigm for applications of multi-photon absorption in the therapeutic delivery of NO.

Direct Imaging the Upconversion Nanocrystal Core/Shell Structure at the Subnanometer Level: Shell Thickness Dependence in Upconverting Optical Properties

Lanthanide-doped upconversion nanoparticles have shown considerable promise in solid-state lasers, three-dimensional flat-panel displays, and solar cells and especially biological labeling and imaging. It has been demonstrated extensively that the epitaxial coating of upconversion (UC) core crystals with a lattice-matched shell can passivate the core and enhance the overall upconversion emission intensity of the materials. However, there are few papers that report a precise link between the shell thickness of core/shell nanoparticles and their optical properties. This is mainly because rare earth fluoride upconversion core/shell structures have only been inferred from indirect measurements to date. Herein, a reproducible method to grow a hexagonal NaGdF(4) shell on NaYF(4):Yb,Er nanocrystals with monolayer control thickness is demonstrated for the first time. On the basis of the cryo-transmission electron microscopy, rigorous electron energy loss spectroscopy, and high-angle annular dark-field investigations on the core/shell structure under a low operation temperature (96 K), direct imaging the NaYF(4):Yb,Er@NaGdF(4) nanocrystal core/shell structure at the subnanometer level was realized for the first time. Furthermore, a strong linear link between the NaGdF(4) shell thickness and the optical response of the hexagonal NaYF(4):Yb,Er@NaGdF(4) core/shell nanocrystals has been established. During the epitaxial growth of the NaGdF(4) shell layer by layer, surface defects of the nanocrystals can be gradually passivated by the homogeneous shell deposition process, which results in the obvious enhancement in overall UC emission intensity and lifetime and is more resistant to quenching by water molecules.

Upconversion Nanomaterials: Synthesis, Mechanism, and Applications in Sensing

Upconversion is an optical process that involves the conversion of lower-energy photons into higher-energy photons. It has been extensively studied since mid-1960s and widely applied in optical devices. Over the past decade, high-quality rare earth-doped upconversion nanoparticles have been successfully synthesized with the rapid development of nanotechnology and are becoming more prominent in biological sciences. The synthesis methods are usually phase-based processes, such as thermal decomposition, hydrothermal reaction, and ionic liquids-based synthesis. The main difference between upconversion nanoparticles and other nanomaterials is that they can emit visible light under near infrared irradiation. The near infrared irradiation leads to low autofluorescence, less scattering and absorption, and deep penetration in biological samples. In this review, the synthesis of upconversion nanoparticles and the mechanisms of upconversion process will be discussed, followed by their applications in different areas, especially in the biological field for biosensing.

Multifunctional Core–Shell Upconverting Nanoparticles for Imaging and Photodynamic Therapy of Liver Cancer Cells

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted considerable attention for their application in biomedicine. Here, silica-coated NaGdF(4):Yb,Er/NaGdF(4) nanoparticles with a tetrasubstituted carboxy aluminum phthalocyanine (AlC(4)Pc) photosensitizer covalently incorporated inside the silica shells were prepared and applied in the photodynamic therapy (PDT) and magnetic resonance imaging (MRI) of cancer cells. These UCNP@SiO(2)(AlC(4)Pc) nanoparticles were uniform in size, stable against photosensitizer leaching, and highly efficient in photogenerating cytotoxic singlet oxygen under near-infrared (NIR) light. In vitro studies indicated that these nanoparticles could effectively kill cancer cells upon NIR irradiation. Moreover, the nanoparticles also demonstrated good MR contrast, both in aqueous solution and inside cells. This is the first time that NaGdF(4):Yb,Er/NaGdF(4) upconversion-nanocrystal-based multifunctional nanomaterials have been synthesized and applied in PDT. Our results show that these multifunctional nanoparticles are very promising for applications in versatile imaging diagnosis and as a therapy tool in biomedical engineering.

Intracellular Glutathione Detection Using MnO2-Nanosheet-Modified Upconversion Nanoparticles

We report a novel design, based on a combination of lanthanide-doped upconversion nanoparticles and manganese dioxide nanosheets, for rapid, selective detection of glutathione in aqueous solutions and living cells. In this approach, manganese dioxide (MnO(2)) nanosheets formed on the surface of nanoparticles serve as an efficient quencher for upconverted luminescence. The luminescence can be turned on by introducing glutathione that reduces MnO(2) into Mn(2+). The ability to monitor the glutathione concentration intracellularly may enable rational design of a convenient platform for targeted drug and gene delivery.

Research Spotlight: Upconversion Nanoparticles for Potential Cancer Theranostics

Lanthanide-doped upconversion nanoparticles have recently attracted significant interest in the field of biomedicine. In the past 2 years, our group has been studying the applications of upconversion nanoparticles in biomedical imaging and drug delivery, as well as imaging-guided novel cancer therapies.

Polymer-Coated NaYF4:Yb3+, Er3+ Upconversion Nanoparticles for Charge-Dependent Cellular Imaging

Lanthanide-doped upconversion nanoparticles (UCNPs) are considered promising novel near-infrared (NIR) bioimaging agents with the characteristics of high contrast and high penetration depth. However, the interactions between charged UCNPs and mammalian cells have not been thoroughly studied, and the corresponding intracellular uptake pathways remain unclear. Herein, our research work involved the use of a hydrothermal method to synthesize polyvinylpyrrolidone-coated UCNPs (UCNP-PVP), and then a ligand exchange reaction was performed on UCNP-PVP, with the help of polyethylenimine (PEI) and poly(acrylic acid) (PAA), to generate UCNP-PEI and UCNP-PAA. These polymer-coated UCNPs demonstrated good dispersibility in aqueous medium, had the same elemental composition and crystal phase, shared similar TEM and dynamic light scattering (DLS) size distribution, and exhibited similar upconversion luminescence efficiency. However, the positively charged UCNP-PEI evinced greatly enhanced cellular uptake in comparison with its neutral or negative counterparts, as shown by multiphoton confocal microscopy and inductively coupled plasma mass spectrometry (ICP-MS) measurements. Meanwhile, we found that cationic UCNP-PEI can be effectively internalized mainly through the clathrin endocytic mechanism, as revealed by colocalization, chemical, and genetic inhibitor studies. This study elucidates the role of the surface polymer coatings in governing UCNP-cell interactions, and it is the first report on the endocytic mechanism of positively charged lanthanide-doped UCNPs. Furthermore, this study provides important guidance for the development of UCNPs as specific intracellular nanoprobes, allowing us to control the UCNP-cell interactions by tuning surface properties.