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Journal ArticleDOI

Upconversion luminescence imaging of cells and small animals

Qian Liu1, Wei Feng1, Tianshe Yang1, Tao Yi1, Fuyou Li1 
01 Oct 2013-Nature Protocols (Nature Research)-Vol. 8, Iss: 10, pp 2033-2044
TL;DR: A step-by-step guide for the fabrication of UCL probes, including lanthanide-based upconversion nanoparticles (Ln-UCNPs) with a particle size of ∼20 nm, and the synthesis of hydrophilic UCNP for application in UCL bioimaging requires ∼15 d.
Abstract: Upconversion luminescence (UCL) is an anti-Stokes process whereby low-energy photons are converted to higher-energy ones. UCL imaging for cells and animal tissues has attracted substantial attention in recent years because of the unique abilities of upconversion materials, which can minimize the background interference from the autofluorescence of biosamples and enhance tissue penetration. This protocol describes a step-by-step guide for the fabrication of UCL probes, including lanthanide-based upconversion nanoparticles (Ln-UCNPs) with a particle size of ∼20 nm (NaYF4/NaLuF4: Yb, Er/Tm) and triplet-triplet annihilation-based UCNPs (TTA-UCNPs) with a particle size of ∼10 nm (palladium octaethylporphyrin as sensitizer and 9,10-diphenylanthracene as annihilator). We also describe the characterization of the UCL nanoprobes (via transmission electron microscopy and UCL emission spectroscopy) and functionalization (via silica coating and ligand exchange), as well as applications for UCL bioimaging of living cells (HeLa cells) and small animals (nude mice and Kunming mice). The setup of a laser-scanning UCL microscope and a UCL imaging system is also presented. Compared with a normal imaging setup, we adopted longer-wavelength excitation lasers and short-pass filters. The synthesis of hydrophilic UCNP for application in UCL bioimaging requires ∼15 d.
Citations
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Journal ArticleDOI
Jing Zhou1, Qian Liu1, Wei Feng1, Yun Sun1, Fuyou Li1 

1,679 citations

Journal ArticleDOI
Wei Zheng1, Ping Huang1, Datao Tu1, En Ma1, Haomiao Zhu1, Xueyuan Chen1 
TL;DR: This review focuses on the most recent advances in the development of lanthanide-doped UCNPs as potential luminescent nano-bioprobes by means of the authors' customized lanthanides photophysics measurement platforms specially designed for upconversion luminescence.
Abstract: Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted considerable interest due to their superior physicochemical features, such as large anti-Stokes shifts, low autofluorescence background, low toxicity and high penetration depth, which make them extremely suitable for use as alternatives to conventional downshifting luminescence bioprobes like organic dyes and quantum dots for various biological applications. A fundamental understanding of the photophysics of lanthanide-doped UCNPs is of vital importance for discovering novel optical properties and exploring their new applications. In this review, we focus on the most recent advances in the development of lanthanide-doped UCNPs as potential luminescent nano-bioprobes by means of our customized lanthanide photophysics measurement platforms specially designed for upconversion luminescence, which covers from their fundamental photophysics to bioapplications, including electronic structures (energy levels and local site symmetry of emitters), excited-state dynamics, optical property designing, and their promising applications for in vitro biodetection of tumor markers. Some future prospects and efforts towards this rapidly growing field are also envisioned.

698 citations

Journal ArticleDOI
TL;DR: This protocol describes the detailed experimental procedure for synthesizing core-shell NaGdF4 nanoparticles that incorporate lanthanide ions into different layers for efficiently converting a single-wavelength, near-IR excitation into a tunable visible emission.
Abstract: Sodium gadolinium fluoride (NaGdF4) is an ideal host material for the incorporation of luminescent lanthanide ions because of its high photochemical stability, low vibrational energy and its ability to mediate energy exchanges between the lanthanide dopants This protocol describes the detailed experimental procedure for synthesizing core-shell NaGdF4 nanoparticles that incorporate lanthanide ions into different layers for efficiently converting a single-wavelength, near-IR excitation into a tunable visible emission These nanoparticles can then be used as luminescent probes in biological samples, in 3D displays, in solar energy conversion and in photodynamic therapy The NaGdF4 nanoparticles are grown through co-precipitation in a binary solvent mixture of oleic acid and 1-octadecene Doping by lanthanides with controlled compositions and concentrations can be achieved concomitantly with particle growth The lanthanide-doped NaGdF4 nanoparticles then serve as seed crystals for subsequent epitaxial growth of shell layers comprising different lanthanide dopants The entire procedure for the preparation and isolation of the core-shell nanoparticles comprising two epitaxial shell layers requires ∼15 h for completion

485 citations

Journal ArticleDOI
TL;DR: The different mechanisms responsible for the upconversion process, and methods that are used to synthesize and decorate upconverting nanoparticles are presented to indicate how absorption and emission can be tuned.

328 citations

References
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Journal ArticleDOI
TL;DR: Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT and were linked to thermal population of energy states above excitation states by such an energy amount.
Abstract: Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

4,279 citations

Journal ArticleDOI
01 Sep 2005-Nature
TL;DR: A unified approach to the synthesis of a large variety of nanocrystals with different chemistries and properties and with low dispersity is reported, based on a general phase transfer and separation mechanism occurring at the interfaces of the liquid, solid and solution phases present during the synthesis.
Abstract: New strategies for materials fabrication are of fundamental importance in the advancement of science and technology. Organometallic and other organic solution phase synthetic routes have enabled the synthesis of functional inorganic quantum dots or nanocrystals. These nanomaterials form the building blocks for new bottom-up approaches to materials assembly for a range of uses; such materials also receive attention because of their intrinsic size-dependent properties and resulting applications. Here we report a unified approach to the synthesis of a large variety of nanocrystals with different chemistries and properties and with low dispersity; these include noble metal, magnetic/dielectric, semiconducting, rare-earth fluorescent, biomedical, organic optoelectronic semiconducting and conducting polymer nanoparticles. This strategy is based on a general phase transfer and separation mechanism occurring at the interfaces of the liquid, solid and solution phases present during the synthesis. We believe our methodology provides a simple and convenient route to a variety of building blocks for assembling materials with novel structure and function in nanotechnology.

2,418 citations

Journal ArticleDOI
03 Apr 2008-Nature
TL;DR: Advances in experimental and clinical imaging are likely to improve how cancer is understood at a systems level and should enable doctors not only to locate tumours but also to assess the activity of the biological processes within these tumours and to provide 'on the spot' treatment.
Abstract: New technologies for imaging molecules, particularly optical technologies, are increasingly being used to understand the complexity, diversity and in vivo behaviour of cancers. 'Omic' approaches are providing comprehensive 'snapshots' of biological indicators, or biomarkers, of cancer, but imaging can take this information a step further, showing the activity of these markers in vivo and how their location changes over time. Advances in experimental and clinical imaging are likely to improve how cancer is understood at a systems level and, ultimately, should enable doctors not only to locate tumours but also to assess the activity of the biological processes within these tumours and to provide 'on the spot' treatment.

2,135 citations

Journal ArticleDOI
TL;DR: By rational design of a core-shell structure with a set of lanthanide ions incorporated into separated layers at precisely defined concentrations, efficient upconversion emission can be realized through gadolinium sublattice-mediated energy migration for a wide range of Lanthanide activators without long-lived intermediary energy states.
Abstract: Photon upconversion is promising for applications such as biological imaging, data storage or solar cells. Here, we have investigated upconversion processes in a broad range of gadolinium-based nanoparticles of varying composition. We show that by rational design of a core-shell structure with a set of lanthanide ions incorporated into separated layers at precisely defined concentrations, efficient upconversion emission can be realized through gadolinium sublattice-mediated energy migration for a wide range of lanthanide activators without long-lived intermediary energy states. Furthermore, the use of the core-shell structure allows the elimination of deleterious cross-relaxation. This effect enables fine-tuning of upconversion emission through trapping of the migrating energy by the activators. Indeed, the findings described here suggest a general approach to constructing a new class of luminescent materials with tunable upconversion emissions by controlled manipulation of energy transfer within a nanoscopic region.

1,528 citations

Journal ArticleDOI
TL;DR: In this critical review, recent reports regarding the synthesis of water-soluble UCNPs and their surface modification and bioconjugation chemistry are summarized and the applications ofUCNPs for small-animal imaging, including tumor-targeted imaging, lymphatic imaging, vascular imaging and cell tracking are reviewed in detail.
Abstract: 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).

1,442 citations