Lanthanide-doped Nanoparticles Research Articles

Luminescence Lifetime Imaging Based on Lanthanide Nanoparticles

AbstractLuminescence lifetime imaging has exhibited significant advantages over traditional optical imaging in terms of precise quantification detection because of the intrinsic stability of luminescence lifetimes. Recently, great emphasis has been put on the exploration of lanthanide‐doped nanoparticles (LnNPs) with long‐lived luminescence. The long luminescence lifetime of LnNPs not only makes it easier to filter out background signals during imaging, but also provides a wide range of tunable lifetime. Here, we introduce the luminescence mechanisms of LnNPs, the key strategies for luminescence lifetime modulation, data acquisition methods, and several cutting‐edge applications in lifetime imaging systems. Then we describe several prospects to inspire efforts for improving technologies and extending applications of luminescence lifetime imaging.

Luminescence Lifetime Imaging Based on Lanthanide Nanoparticles.

Luminescence lifetime imaging has exhibited significant advantages over traditional optical imaging in terms of precise quantification detection because of the intrinsic stability of luminescence lifetimes. Recently, great emphasis has been put on the exploration of lanthanide-doped nanoparticles (LnNPs) with long-lived luminescence. The long luminescence lifetime of LnNPs not only makes it easier to filter out background signals during imaging, but also provides a wide range of tunable lifetime. Here, we introduce the luminescence mechanisms of LnNPs, the key strategies for luminescence lifetime modulation, data acquisition methods, and several cutting-edge applications in lifetime imaging systems. Then we describe several prospects to inspire efforts for improving technologies and extending applications of luminescence lifetime imaging.

Lanthanide-doped niobium oxide nanoparticles on nanoarchitectured silica spheres as potential probe for NIR luminescent markers

We have prepared Nb2O5:Eu3+ and Nb2O5:Nd3+ nanostructured materials and SiO2@Nb2O5:Eu3+ core@shell nanoparticles by the sol–gel route to evaluate how the annealing temperature influences their structural and luminescent features, aiming at their potential application as optical markers. An intense red emission under excitation at the blue region was detected from the Nb2O5:Eu3+ solids. Inhomogeneous broadening on the photoluminescence spectra was observed for the sample annealed at 600 °C, while the allocation of the Eu3+ ions on S4 symmetry sites was attributed for higher annealing temperature (1100 °C). A discrete formation of the H-phase (monoclinic) of niobium oxide for the sample annealed at an intermediate temperature of 900 °C was observed, with its photoluminescence spectra revealing the preferential occupation of the Eu3+ ions on sites in this crystalline phase. Photoluminescence decay curves recorded for the 5D0 excited state revealed average lifetime values in the order of milliseconds. The Nb2O5:Nd3+ solids displayed analogous behavior: Nd3+ preferentially occupied the monoclinic phase symmetry sites. In water dispersion and under low-power laser excitation (808 nm), the Nb2O5:Nd3+ systems emitted in biological windows. The sample annealed at 600 °C provided the most promising luminescence intensity and colloidal stability. The surface of the SiO2 nanoparticles was successfully decorated with Nb2O5:Eu3+ nanoparticles in the T-phase. The SiO2@Nb2O5:Eu3+ core@shell nanoparticles presented color tunability due to red light emission from Eu3+ and blue light emission from defect centers in the SiO2 template. The possibility of functionalizing SiO2 nanoparticles with red-emitting Nb2O5:Eu3+ nanoparticles combined with blue excitation and lifetime values in the order of milliseconds renders the prepared SiO2@Nb2O5:Eu3+ core@shell nanoparticles promising biomarkers that can be explored by time-gated luminescence techniques.

Coumarin derivative dye sensitized NaYGdF4:Yb,Er nanoparticles with enhanced NIR II luminescence for bio-vascular imaging

Lanthanide-doped biocompatible nanoparticles have promising applications in near-infrared second region imaging due to their high chemical stability, enhanced photostability and sharp emission bandwidth. However, the weak light absorption capacity limits the application of rare-earth nanoparticles (RENPs) for bioimaging. We prepared a coumarin-derived dye sensitized NaYGdF4:Yb,Er nanoparticle probe, in which the organic dye enhances photon absorption through the sensitization process, improving the luminescence efficiency of the rare earth particles near 1000 and 1500 nm. In addition, good water solubility and stability of the probe are imparted by coating the particles with amphiphilic polymers distearoyl phosphatidylethanolamine-polyethylene glycol (DSPE-PEG) and polyacrylic acid. This composite probe with good biocompatibility and NIR II luminescence properties can be used for vascular imaging, providing a tool for the detection of hematologic-related diseases.

Immobilization of strontium aluminate nanoparticles onto plasma-pretreated nonwoven polypropylene fibers by screen-printing toward photochromic textiles

Polypropylene fibers have been applied in various fields, such as automotives, plastic furniture, medical devices, and food packaging. Polypropylene fibers are characterized by low-cost, high flexural and impact strength, as well as high resistant to chemicals, moisture, fade, electricity and fatigue. However, polypropylene fiber is inherently resistant to stain because they have no active dyeing sites on their surface. Therefore, it has been impossible to dye polypropylene fibers after extrusion. In the current study, we introduce a novel strategy toward the production of photoluminescent nonwoven polypropylene fabrics by plasma-assisted screen-printing with rare-earth doped strontium aluminate nanoparticles. Aqueous-based phosphor-binder printing paste was applied directly onto nonwoven polypropylene textiles. The superhydrophobic properties of the phosphor-printed nonwoven polypropylene textile substrates were enhanced with increasing the phosphor ratio in the printing paste. Both of ultraviolet protection and antibacterial activity of the phosphor-printed nonwoven polypropylene fabrics were also considered. The produced colorless photoluminescent layer displayed an emission band at 515 nm after being excited at 371 nm. The phosphor-printed fabrics exhibited various colorimetric shades, including off-white beneath daylight and green beneath ultraviolet lamp, as proved by photoluminescence spectra and CIE Lab properties. The comfortability was inspected by testing both of air-permeability and bend length to indicate good flexibility and breathability. The phosphor nanoparticles were studied for their morphological properties to display diameters of 4–9 nm. The spectroscopic findings of the phosphor-printed nonwoven polypropylene were explored. The colorfastness was studied to indicate high durability. The phosphor-printed fabrics showed good reversibility and fatigue-resistance.

Upconversion FRET quantitation: the role of donor photoexcitation mode and compositional architecture on the decay and intensity based responses

Lanthanide-doped colloidal nanoparticles capable of photon upconversion (UC) offer long luminescence lifetimes, narrowband absorption and emission spectra, and efficient anti-Stokes emission. These features are highly advantageous for Förster Resonance Energy Transfer (FRET) based detection. Upconverting nanoparticles (UCNPs) as donors may solve the existing problems of molecular FRET systems, such as photobleaching and limitations in quantitative analysis, but these new labels also bring new challenges. Here we have studied the impact of the core-shell compositional architecture of upconverting nanoparticle donors and the mode of photoexcitation on the performance of UC-FRET from UCNPs to Rose Bengal (RB) molecular acceptor. We have quantitatively compared luminescence rise and decay kinetics of Er3+ emission using core-only NaYF4: 20% Yb, 2% Er and core-shell NaYF4: 20% Yb @ NaYF4: 20% Yb, 5% Er donor UCNPs under three photoexcitation schemes: (1) direct short-pulse photoexcitation of Er3+ at 520 nm; indirect photoexcitation of Er3+ through Yb3+ sensitizer with (2) 980 nm short (5–7 ns) or (3) 980 nm long (4 ms) laser pulses. The donor luminescence kinetics and steady-state emission spectra differed between the UCNP architectures and excitation schemes. Aiming for highly sensitive kinetic upconversion FRET-based biomolecular assays, the experimental results underline the complexity of the excitation and energy-migration mechanisms affecting the Er3+ donor responses and suggest ways to optimize the photoexcitation scheme and the architecture of the UCNPs used as luminescent donors.

Complement-Opsonized NIR-IIb Emissive Immunotracers for Dynamically Monitoring Neutrophils in Inflammation-Related Diseases.

Real-time monitoring of neutrophil dynamics is crucial for timely diagnosis and effective treatment of inflammation-related diseases, which requires a reliable tracer for in vivo tracking of neutrophils. However, immunotracers for neutrophils are extremely limited because of the difficulty in labeling the cells. Inspired by the natural biological function of the complement system, a strategy of enhancing the complement C3 opsonization of lanthanide-doped nanoparticles (LnNPs) by modulating their surface chemistry, thus developing a near infrared-IIb emissive nanotracer for neutrophils, is reported herein. Four kinds of surface-modified LnNPs are fabricated, among which phospholipids DOPG-modified LnNPs (LnNPs@PG) with weak antifouling ability and hydroxyl groups adsorb more complement C3 proteins and form covalent linkages with C3b active fragments under inflammation conditions, inducing enhanced complement C3 opsonization. Therefore, LnNPs@PG with enhanced complement C3 opsonization are capable of efficiently labeling inflammation-stimulated neutrophils in vivo through complement-receptors-mediated phagocytosis and achieve dynamic monitoring neutrophils during cutaneous wound healing and cerebral ischemia/reperfusion.

Photoswitchable lanthanide-doped core-multishell nanoparticles for tunable triple-mode information encryption and dynamic anti-counterfeiting patterns

Photoresponsive luminescent materials with high-capacity information storage and multilevel anti-counterfeiting capability are attracting much interest in many fields including information encryption and anti-counterfeiting. Herein, a class of novel photoswitchable upconversion luminescent nanoparticles (PUCNPs) with core-multishell structure that shows switchable dual-colored emission is described. The PUCNPs is successively built up from lanthanide-doped NaYF4 nanoparticles and a photochromic spiropyrane (SP) monomer by grafting of poly(glycidyl methacrylate-co-SPMA) on the nanoparticles via surface reversible addition-fragmentation chain transfer (RAFT) polymerization. The as-prepared PUCNPs with triple-mode optical features displayed green upconversion luminescence under a 980 nm laser, red downconervsion fluorescence and purple color under a 365 nm UV light irradiation and turning off, respectively. Furthermore, they enable dynamic reversible changes in color between colorless and purple states with 365 nm UV and white light stimuli. Their potential in complex information encryption and dynamic anti-counterfeiting patterns is described and its great potential in data storage, and rewritable optical materials is foreseen.

Structural and optical investigations in undoped and rare-earth doped zinc oxide nanoparticles for photon upconversion based applications

The present work reports comprehensive investigations of the physical properties of undoped and rare-earth (RE3+) doped ZnO based upconversion nanoparticles. X-ray diffraction analysis of these nanoparticles reveals the hexagonal wurtzite structure. The induced-strain value of the RE3+ doped ZnO nanoparticles increased by almost one order of magnitude, and their mean particle size reduced from 36 nm to 17 nm. The scanning electron microscopic images showed that the particles retained the spherical shape in the undoped and doped conditions. The elemental maps confirmed the uniform distribution of the RE3+ dopants. The recorded absorbance spectrum for the doped nanoparticles showed significant absorption in ultraviolet and near infra-red regions owing to the band-band transitions and the deep defect level transitions that are induced due to intrinsic and extrinsic defect states. A detailed analysis of the defect states of these samples is described based on the Urbach energy studies. An intense peak observed at 980 nm suggests the possibility of photon upconversion in the doped nanoparticles. A simplified energy diagram (as depicted below) has demonstrated the multi-photon absorption and possible upconversion mechanisms. The optical absorption spectrum of RE3+ doped ZnO nanocrystals encourages the promising application of these materials in diverse fields, particularly in biomedical and photovoltaic applications.

(Invited) Exploring in the Near Infrared: From Quantum Dots to Rare-Earth Doped Nanoparticles

Bioimaging shows great potential for disease detection due to its high sensitivity at the subcellular level and low cost of related imaging facilities. As compared to most commonly used optical probes that are excited and emit in the visible wavelength range, near-infrared (NIR) excitable and emitting nanomaterials are indeed more promising for bioimaging. It is because at certain NIR wavelengths (known as biological windows) tissues are basically optically transparent and show minimal scattering and absorption, allowing for deep tissue imaging. Meanwhile, tissue autofluorescence can also be avoided. In this talk, I will present our recent work [1-4] on the synthesis of NIR-emitting water soluble, stable core/shell/shell quantum dots (QDs) and rare-earth doped nanoparticles, and their use in biomedicine, including but not limited to bioimaging.

(Invited) Multi-Architectured Lanthanide Doped Nanoparticles for Theranostics

Light triggered theranostic (therapy and diagnostic) nanoplatforms have gained a considerable attention in recent years. In theranostics, light as an external trigger stands out due to its non-invasiveness, high local precision and temporal resolution. Many such nanoplatforms employ high-energy (visible or UV) light to initiate the individual therapeutic and diagnostic modalities. However, light at these wavelengths suffers from inherent drawbacks such as having little to no penetration in living tissue, inducing autofluorescence from inherent fluorophores or chromophores in tissues and causing photodamage. The use of near-infrared (NIR) light for excitation mitigates such drawbacks associated with high-energy excitation, for example, little to no background autofluorescence from the specimen under investigation as well as no incurred photodamage. Moreover, one of the biggest limitations is that of penetration and NIR light can penetrate tissues much better than high-energy light especially when these wavelengths lie within the three biological windows where tissues are optically transparent. At the forefront of NIR excited nanomaterials are lanthanide doped nanoparticles, which can undergo conventional (Stokes) luminescence and emit in the NIR biological windows. However, unlike other classes of nanoparticles, they can also undergo a multiphoton excitation process where the NIR excitation light is converted to higher energies resulting in anti-Stokes luminescence spanning the UV-visible-NIR regions (known as upconversion). Thus, it now becomes possible to generate upconverted high-energy light (UV or visible) in situ to trigger other light activated therapeutic modalities (i.e. drug release) while using the NIR emission for diagnostics (i.e. bioimaging, nanothermometry). Here, we demonstrate how the luminescence properties (upconversion and NIR) of various lanthanide doped core/shell (and multishell) nanoparticles can be exploited for potential use in theranostics.

Luminescence thermometry with rare earth doped nanoparticles: Status and challenges

Luminescence thermometry is a unique temperature detection technology with remote and noncontact functions. Rare earth doped materials have been widely used for luminescent thermometers due to their chemical stability and non-blinking properties. With rapid development of the nanoscience and nanotechnology, rare earth doped nanoparticles (RE-doped NPs) have emerged as good candidates for luminescence thermometry by providing high spatial resolution and wide temperature detection ranges. In this report, we focus on the principles and applications of RE-doped NPs for Luminescence thermometry and present recent advances, challenges, and perspectives.

Upconversion semiconductor interfaces by wafer bonding for photovoltaic applications

Efficient use of incident sunlight is an important key issue for the improvement of solar cell performance. Here, we propose and experimentally demonstrate photon upconversion material mediated semiconductor bonding as a concept of interfacial functionalization. Our wavelength-converting semiconductor interface comprises rare earth doped upconversion nanoparticles embedded in a hydrogel matrix. Advantageously, the bonding process is conducted at room temperature in ambient air. As a proof of principle, photocurrent enhancement in bonded Si solar cells is demonstrated. Our technical scheme could be useful to improve the performance and structural flexibility of various optoelectronic devices by delivering the preferred frequency to each of the optical components.

Boosting overall electrochemical water splitting via rare earth doped cupric oxide nanoparticles obtained by co-precipitation technique

The development of electrocatalyst based on nonprecious metals has been a persistent issue as electrochemical water splitting requires electrocatalyst with advanced activity and stability. Further, the electrocatalyst must require low overpotential above the standard potential (>1.23 V) of water splitting to produce hydrogen. This study presents the facile co-precipitation derived rare earth dysprosium (Dy) doped cupric oxide nanoparticles (Cu1−xDyxO) as a non-noble transition metal oxide nanoparticle. The 3 % Dy doped CuO (3 % Dy/CuO) and 1 % Dy doped CuO (1 % Dy/CuO) electrocatalysts showed excellent Oxygen Evolution Reaction (OER) at 1.55 V vs RHE and Hydrogen Evolution Reaction (HER) at − 0.036 V vs RHE in aqueous 1 M KOH aqueous electrolyte to attain the benchmark current density (10 mA cm−2). The stability of the driven electrocatalyst in a bi-functional electrocatalytic setup was monitored for 24 h and was found to be exhibiting a cell voltage of about 2.1 V at 30 mA cm−2 constant current density. Further, the retention capability of the electrode was observed to be 99 % with a very minimal loss. This study hugely suggests the promising consequence of doping rare earth onto a non-precious metal oxide-based electrocatalyst, making it a highly effective bifunctional material for water splitting.

Brain Tumor Cell Membrane-Coated Lanthanide-Doped Nanoparticles for NIR-IIb Luminescence Imaging and Surgical Navigation of Glioma.

Intraoperative visualization of the full extent of brain tumor by luminescence imaging helps to improve the degree and accuracy of brain tumor resection, thereby prolonging the survival of patients. However, the limited imaging depth and spatial resolution and the poor blood-brain barrier (BBB) permeability of most currently available luminescent probes restrict the imaging performance and surgical resection efficiency of brain tumor. Here, a brain tumor cell membrane-coated lanthanide-doped nanoparticles (CC-LnNPs) in the near-infrared-IIb window (NIR-IIb, 1500-1700nm) is designed for brain tumor imaging and surgical navigation. The coating of brain tumor cell membrane endows CC-LnNPs with immune escape, BBB crossing, and homotypic targeting abilities, which are inherited from the source brain tumor cells. In addition, compared with clinically approved imaging agent indocyanine green, CC-LnNPs present higher temporal and spatial resolution, higher stability, and lower background signals, enabling clear visualization of the brain tumor boundary. With the guidance of NIR-IIb fluorescence, the glioma tissue (size<3mm, depth>3mm) could be clearly visualized and completely removed as a proof of concept. This study offers new insight for the future design of nanoprobe to image brain tumor and to achieve precise diagnosis and surgical navigation of brain tumor.

Calibration of upconversion luminescence of lanthanide-doped nanoparticle suspensions using Raman scattering.

A new, to the best of our knowledge, internal reference method has been developed for the study of the upconversion luminescence of nanoparticle suspensions. This method provides correct analysis and comparison of the luminescent signals obtained under different conditions. To excite the echo signals of samples, it is proposed to use the radiation from an optical parametric oscillator at two wavelengths for the simultaneous excitation of the upconversion luminescence of particles and the Raman scattering signal of the medium in the Stokes region of the spectrum. Due to the linear dependence of the intensity of the Raman scattering of the medium on the excitation power density, the normalization of the upconversion luminescence signal of particles to the intensity of the Raman scattering of the medium makes it possible to eliminate the influences of the instability of the intensity of the laser radiation, light scattering by the medium, inaccuracies in alignment, etc. on the luminescence signal.

Fabricating ultralow-power-excitable lanthanide-doped inorganic nanoparticles with anomalous thermo-enhanced photoluminescence behavior

Trivalent lanthanide (Ln3+)-doped luminescent nanoparticles (NPs) have been extensively investigated as deep-tissue-penetration visual bioimaging agents owing to their exceptional upconversion and near-infrared (NIR) luminescence upon irradiation of NIR light. However, in most cases, the power density of irradiation used for in vivo biological imaging is much higher than that of the reported maximum permissible exposure (MPE) value of NIR light, which inevitably does great damage to the living organisms under study and thus impedes the plausible clinical applications. Herein, by using a facile syringe pump-aided shell epitaxial growth method, we construct for the first time a new class of Ln3+-doped KMgF3:Yb/Er@KMgF3 core-shell NPs that can be activated by utilizing a 980-nm xenon lamp or diode laser with an ultralow excitation power density down to 0.08 mW cm−2, a value that is approximately 4 orders of magnitude lower than the MPE value set by the American National Standards Institute (ANSI) for safe bioimaging in vivo. By combining the comparative spectroscopic investigations with atomic-resolved spherical aberration corrected transmission electron microscopy (AC-TEM) characterization, we find that the reduced crystallographic defects are the primary cause underlying such an ultralow-power-excitable feature of the KMgF3: Yb/Er@KMgF3 core-shell NPs. And, by the same token, the resultant KMgF3:Yb/Er@KMgF3 core-shell NPs also exhibit an anomalous thermo-enhanced photoluminescence (PL) behavior coupled with an excellent photothermal stability that cannot occur in other Ln3+-doped core-shell NPs. These findings described here unambiguously pave a new way to prepare high-quality Ln3+-doped luminescent NPs with desirable ultralow-power-excitable capability and photothermal stability for future biomedical applications.

Lanthanide-doped heterostructured nanocomposites toward advanced optical anti-counterfeiting and information storage

The continuously growing importance of information storage, transmission, and authentication impose many new demands and challenges for modern nano-photonic materials and information storage technologies, both in security and storage capacity. Recently, luminescent lanthanide-doped nanomaterials have drawn much attention in this field because of their photostability, multimodal/multicolor/narrowband emissions, and long luminescence lifetime. Here, we report a multimodal nanocomposite composed of lanthanide-doped upconverting nanoparticle and EuSe semiconductor, which was constructed by utilizing a cation exchange strategy. The nanocomposite can emit blue and white light under 365 and 394 nm excitation, respectively. Meanwhile, the nanocomposites show different colors under 980 nm laser excitation when the content of Tb3+ ions is changed in the upconversion nanoparticles. Moreover, the time-gating technology is used to filter the upconversion emission of a long lifetime from Tb3+ or Eu3+, and the possibilities for modulating the emission color of the nanocomposites are further expanded. Based on the advantage of multiple tunable luminescence, the nanocomposites are designed as optical modules to load optical information. This work enables multi-dimensional storage of information and provides new insights into the design and fabrication of next-generation storage materials.

Intensifying Upconverted Ultraviolet Emission towards Efficient Reactive Oxygen Species Generation.

Multiphoton upconversion that can convert near-infrared irradiation into ultraviolet emission offers many unique opportunities for photocatalysis and phototherapy. However, the high-lying excited states of lanthanide emitters are often quenched by the interior lattice defects and deleterious interactions among different lanthanides, resulting in weak ultraviolet emission. Here, we describe a novel excitation energy lock-in approach to boost ultraviolet upconversion emission in a new class of multilayer core-shell nanoparticles with a gadolinium-rich core domain. Remarkably, we observe more than 70-fold enhancements in Gd3+ emission from the designed nanoparticles compared with the conventional nanoparticles. Our mechanistic investigation reveals that the combination of energy migration over the core domain and optically inert NaYF4 interlayer can effectively confine the excitation energy and thus lead to intense multiphoton ultraviolet emission in upconversion nanostructures. We further achieve a 35.6% increase in photocatalytic reactivity and 26.5% in reactive oxygen species production yield in ZnO-coated upconversion nanocomposites under 808-nm excitation. This study provides a new insight to energy transfer mechanism in lanthanide-doped nanoparticles and offers an exciting avenue for exploring novel near-infrared photocatalysts.

Catalytic Chiral Photochemistry Sensitized by Chiral Hosts-Grafted Upconverted Nanoparticles.

Singlet chiral photocatalysis is highly challenging. Herein, we report fluorescence resonance energy transfer (FRET)-based chiral photocatalysis with γ-cyclodextrin (CD)-grafted lanthanide-doped upconverted nanoparticles (UCNP). The CD-modified UCNP strongly emits in the UV wavelength region upon excitation with a 980 nm laser, which selectively sensitizes the photosubstrates complexed by CD on the surface of UCNP through FRET. Therefore, enantiodifferentiating photocyclodimerization of anthracene or naphthalene derivatives sensitized by the CD-modified UCNP gives photoproducts in good enantioselectivity even in the presence of a catalytic amount of CD-modified UCNP. Moreover, the photocatalysts are readily separated and could be reused for at least six cycles without decreasing the enantioselectivity.