Lanthanide-doped Luminescent Nanoparticles Research Articles

Recent Advances in Triplet Energy Transfer between Organic Dyes and Lanthanide-Doped Luminescent Nanoparticles

Recent Advances in Triplet Energy Transfer between Organic Dyes and Lanthanide-Doped Luminescent Nanoparticles

Color tunable luminescence in ThO2:Er3+,Yb3+ nanocrystals: a promising new platform for upconversion.

Lanthanide-doped luminescent nanoparticles are an appealing system for many applications in the area of biomedical, solar cell, thermometry, anti-counterfeiting, etc. due to their sensitivity, reliability, high photochemical stability, and high optical transparency in the visible-NIR range. A color-tunable upconversion-luminescence (UCL) in a new low phonon energy ThO2 host based on modulating sensitizer concentration has been realized in this work and it may work as a potential candidate to replace corrosive and toxic fluoride based hosts in the future. Er3+-Yb3+ co-doped thoria nanoparticles were prepared using a gel combustion route and their structural and luminescence properties were determined as a function of the Yb3+ concentration. Phonon dispersion measurements have established the dynamic structural stability of the thoria nanoparticles. Density functional theory (DFT) was used to calculate the defect formation energy, highlighting the feasibility of dual ion (Er3+ and Yb3+) doping in thoria. The morphology and average size of the doped thoria was studied using high resolution transmission electron microscopy (HRTEM), and any defects evolving as a result of aliovalent doping were probed using positron annihilation lifetime spectroscopy (PALS). With 980 nm laser excitation, the nanothoria emits green and near-red light. A significant enhancement of the red-to-green intensity ratio of Er3+ ions in nanothoria was observed with an increase in Yb3+ concentration which resulted in beautiful color tunability from green to yellow light in going from lower (up to ∼5 mol%) to higher (10 and 15 mol%) Yb3+ concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two-photon upconversion processes for the green and red emissions.

Optical Bioimaging and Therapy

Optical Bioimaging and Therapy

Optical Manipulation of Lanthanide-Doped Nanoparticles: How to Overcome Their Limitations.

Since Ashkin's pioneering work, optical tweezers have become an essential tool to immobilize and manipulate microscale and nanoscale objects. The use of optical tweezers is key for a variety of applications, including single-molecule spectroscopy, colloidal dynamics, tailored particle assembly, protein isolation, high-resolution surface studies, controlled investigation of biological processes, and surface-enhanced spectroscopy. In recent years, optical trapping of individual sub-100-nm objects has got the attention of the scientific community. In particular, the three-dimensional manipulation of single lanthanide-doped luminescent nanoparticles is of great interest due to the sensitivity of their luminescent properties to environmental conditions. Nevertheless, it is really challenging to trap and manipulate single lanthanide-doped nanoparticles due to the weak optical forces achieved with conventional optical trapping strategies. This limitation is caused, firstly, by the diffraction limit in the focusing of the trapping light and, secondly, by the Brownian motion of the trapped object. In this work, we summarize recent experimental approaches to increase the optical forces in the manipulation of lanthanide-doped nanoparticles, focusing our attention on their surface modification and providing a critical review of the state of the art and future prospects.

Lanthanide-Doped Near-Infrared Nanoparticles for Biophotonics.

Light in the near-infrared (NIR) spectral region is increasingly utilized in bioapplications, providing deeper penetration in biological tissues owing to the lower absorption and scattering in comparison with light in the visible range. Lanthanide-doped luminescent nanoparticles with excitation and/or emission in the NIR range have recently attracted tremendous attention as one of the prime candidates for noninvasive biological applications due to their unique optical properties, such as large Stokes shift, spectrally sharp luminescence emissions, long luminescence lifetimes, and excellent photostability. Herein, recent advances of lanthanide-doped nanoparticles with NIR upconversion or downshifting luminescence and their uses in cutting-edge biophotonic applications are presented. A set of efficient strategies for overcoming the fundamental limit of low luminescence brightness of lanthanide-doped nanoparticles is introduced. An in-depth literature review of their state-of-art biophotonics applications is also included, showing their superiority for high-resolution imaging, single-nanoparticle-level detection, and efficacy for tissue-penetrating diagnostics and therapeutics.

Upconversion nanoparticles coated with molecularly imprinted polymers for specific sensing.

The development of fluorescent sensors based on lanthanide-doped luminescent nanoparticles has increased their application in biomarker detection. Lanthanide-doped upconversion nanoparticles (UCNPs) have been explored as one of the most promising sensors owing to their merits such as excellent photostability, zero background auto-fluorescence, and reduced side effects of near-infrared triggered treatments. However, traditional upconversion luminescence assay based on direct Fluorescence Resonance Energy Transfer (FRET) between the target molecules and surface of UCNPs encounters low detection accuracy due to superficial adsorption interactions. In this work, we use a molecularly imprinting technique to achieve the specific interaction between UCNPs and molecules for accurate sensing. We demonstrate this by synthesizing a nanostructure with a molecularly imprinted polymer at the surface of UCNPs, in which the imprinted cavities can specifically capture the target molecule of rhodamine B. The upconversion signal changes in relation to the molecule concentration due to FRET. Quantitative analysis shows that the fluorescence-quenching rate is consistent with the Stern-Volmer equation, resulting in a limit of detection of 6.27 μg mL-1. Our fluorescence sensing approach integrates the advantages of both nonlinear upconversion and molecular imprinting technologies, showing great potential for the detection of specific molecules.

Induction Heating Efficiency of Water-Dispersible Mn0.5Fe2.5O4@YVO4:Eu3+ Magnetic-Luminescent Nanocomposites in an Acceptable ac Magnetic Field: Hemocompatibility and Cytotoxicity Studies.

Not many reports are available on magnetic-luminescent nanocomposites for cancer hyperthermia applications. Further, such nanocomposites on Mn2+-doped iron oxide may be available rather rarely. Studies on the induction heating properties within the threshold magnetic field and frequency factors are still rare. In most cases, magnetic nanoparticles are studied for hyperthermia and lanthanide-doped luminescent nanoparticles for certain biomedical applications. Here, we report on water-dispersible superparamagnetic manganese-doped iron oxide (Mn0.5Fe2.5O4) nanoparticles and a polyethylene glycol6000-coated magnetic-luminescent nanocomposite. The nanocomposite is composed of magnetic Mn0.5Fe2.5O4 (average size 10-20 nm) nanoparticles and red-emitting YVO4:Eu3+ (average size 40-50 nm) nanoparticles. These magnetic nanoparticles and nanocomposites are studied for their induction heating abilities at different acceptable Hf values ( H, strength of alternating magnetic field and f, the operating frequency). The operational Hf values lie in the ranges of 2.15 × 106 to 4.58 × 106 kA m-1 s-1 that are well below the threshold limit of 5 × 106 kA m-1 s-1. A specific absorption rate as high as 132 and 63 W/g, respectively, for Mn0.5Fe2.5O4 and Mn0.5Fe2.5O4@YVO4:Eu3+, can be achieved. The rate of heating and the temperature achieved with time can be tuned with concentrations as well as magnetic constituents in the nanocomposites. Hemocompatibility analysis revealed high blood compatibility with <5% hemolysis. The cytotoxicity analysis in the MCF-7 cell line showed that the cell viability is 74-85% for 0.2-0.5 mg of the magnetic-luminescent nanocomposites. Beyond this concentration, the percentage of cell death is very high. The red-emitting magnetic-luminescent nanocomposites will be useful for in vitro optical imaging and tracking of magnetic nanoparticles. The magnetization analysis showed that the samples have high enough saturation magnetization and low residual magnetization, which is quite suitable for clinical applications. The water dispersibility, hemocompatibility, and cytotoxicity assay in conjunction with their efficient induction heating abilities have shown that these magnetic-luminescent nanocomposites will have potential applications in magnetic fluid hyperthermia and optical imaging.

ICG‐Sensitized NaYF4:Er Nanostructure for Theranostics

AbstractHere lanthanide‐doped luminescent nanoparticles (LNPs) NaYF4:Er conjugated to the indocyanine green dye (ICG) are introduced for theranostics applications in trimodal imaging as well as in photothermal therapy. ICG as a donor with high absorption cross‐section at 808 nm increases excitation efficiency of Er3+ through the energy transfer mechanism and, therefore, significantly enhances both upconverted and Stokes emissions from Er3+ ions in LNPs. Enhanced Stokes emission is used at 1.5 µm for bioimaging in the second near‐infrared wavelength window, which allows deeper penetration in biological media due to reduced scattering. A part of the ICG excitation decays by the competing nonradiating relaxation to produce local heating, which is utilized for photoacoustic imaging as well as for local thermal imaging. All these modalities are demonstrated by in vivo imaging of subcutaneous pancreatic tumor‐bearing nude mice. Furthermore, in the thermal imaging as well as in vitro photocytotoxicity studies, it is shown that the local temperature rise is high enough to be used for highly effective photothermal therapy. Cytotoxicity study on cells using the MTT assay shows the biocompatibility feature of this nanoconstruct. The obtained results demonstrate the potential of ICG‐NaYF4:Er nanoconjugates for multimodal theranostics.

Ultralow-power near-infrared excited neodymium-doped nanoparticles for long-term in vivo bioimaging.

Lanthanide-doped luminescent nanoparticles with both emission and excitation in the near-infrared (NIR-to-NIR) region hold great promise for bioimaging. Herein, core@shell structured LiLuF4:Nd@LiLuF4 (named as Nd@Lu) nanoparticles (NPs) with highly efficient NIR emission were developed for high-performance in vivo bioimaging. Strikingly, the absolute quantum yield of Nd@Lu NPs reached as high as 32%. After coating with polyethylene glycol (PEG), the water-dispersible Nd@Lu NPs showed good bio-compatibility and low toxicity. With efficient NIR emission, the Nd@Lu NPs were clearly detectable in tissues at depths of up to 20 mm. In addition, long-term in vivo biodistribution with a high signal-to-noise ratio of 25.1 was distinctly tracked upon an ultralow-power-density excitation (10 mW cm-2) of 732 nm for the first time.

Establishing the Structural Integrity of Core-Shell Nanoparticles against Elemental Migration using Luminescent Lanthanide Probes.

Core-shell structured nanoparticles are increasingly used to host luminescent lanthanide ions but the structural integrity of these nanoparticles still lacks sufficient understanding. Herein, we present a new approach to detect the diffusion of dopant ions in core-shell nanostructures using luminescent lanthanide probes whose emission profile and luminescence lifetime are sensitive to the chemical environment. We show that dopant ions in solution-synthesized core-shell nanoparticles are firmly confined in the designed locations. However, annealing at certain temperatures (greater than circa 350 °C) promotes diffusion of the dopant ions and leads to degradation of the integrity of the nanoparticles. These insights into core-shell nanostructures should enhance our ability to understand and use lanthanide-doped luminescent nanoparticles.

Sub‐10 nm Lanthanide‐Doped CaF2 Nanoprobes for Time‐Resolved Luminescent Biodetection

Lanthanide-doped luminescent nanoparticles (NPs) haveevoked considerable interest due to their superior features,such as sharp f–f emission peaks, a long photoluminescence(PL) lifetime, low toxicity, and high resistance to photo-bleaching, which make them extremely suitable for use asalternatives to organic fluorescent dyes or quantum dots forvarious bioapplications.