Nuclear export of PML promotes p53-mediated apoptosis and ferroptosis.

Promyelocytic leukemia protein (PML), a tumor suppressor protein, plays a key role in cell cycle regulation, apoptosis, senescence and cellular metabolism. Here, we report that PML promotes apoptosis and ferroptosis. Our data showed that PML over-expression inhibited cell proliferation and migration. PML over-expression increased apoptotic cells, nuclear condensation and the loss of mitochondrial membrane potential, accompanied by regulation of Bcl-2 family proteins and reactive oxygen species (ROS) level, suggesting that PML enhanced apoptosis. Meanwhile, PML over-expression not only increased lipid ROS accumulation and Malondialdehyde (MDA) content but also downregulated solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4) expression, indicating that PML enhanced ferroptosis. Additionally, knockdown of p53 attenuated the effect of PML on SLC7A11 and GPX4, and inhibited the increase of lipid ROS and ROS by PML over-expression. Moreover, translocation of PML from nucleus to cytoplasm not only promoted apoptosis and ferroptosis, but also inhibited cell proliferation. Taken together, PML promotes apoptosis and ferroptosis, in which the mediation of p53 and the nuclear export of PML play important roles.

Current Developments in Emerging Lanthanide-Doped Persistent Luminescent Scintillators and Their Applications.

Lanthanide-doped scintillators have the ability to convert the absorbed X-ray irradiation into ultraviolet (UV), visible (Vis), or near-infrared (NIR) light. Lanthanide-doped scintillators with excellent persistent luminescence (PersL) are emerging as a new class of PersL materials recently. They have attracted great attention due to their unique "self-luminescence" characteristic and potential applications. In this review, we comb through and focus on current developments of lanthanide-doped persistent luminescent scintillators (PersLSs), including their PersL mechanism, synthetic methods, tuning of PersL properties (e. g. emission wavelength, intensity, and duration time), as well as their promising applications (e. g. information storage, encryption, anti-counterfeiting, bio-imaging, and photodynamic therapy). We hope this review will provide valuable guidance for the future development of PersLSs.

Boosting the Downconversion Luminescence of Tm3+-Doped Nanoparticles for S-Band Polymer Waveguide Amplifier.

Polymer waveguide devices have attracted increasing interest in several rapidly developing areas of broadband communications since they are easily adaptable to on-chip integration and promise low propagation losses. As a key member of the waveguide gain medium, lanthanide doped nanoparticles have been intensively studied to improve the downconversion luminescence. However, current research efforts are almost confined to erbium-doped nanoparticles and amplifiers operating at the C-band; boosting the downconversion luminescence of Tm3+ for S-band optical amplification still remains a challenge. Here we report a Tb3+-induced deactivation control to enhance Tm3+ downconversion luminescence in a stoichiometric Yb lattice without suffering from concentration quenching. We also demonstrate their potential application in an S-band waveguide amplifier and record a maximum optical gain of 18 dB at 1464 nm. Our findings provide valuable insights into the fundamental understanding of deactivation-controlled luminescence enhancement and open up a new avenue toward the development of an S-band polymer waveguide amplifier with high gain.

Three-dimensional, dual-color nanoscopy enabled by migrating photon avalanches with one single low-power CW beam.

The development of super-resolution fluorescence microscopy is very essential for understanding the physical and biological fundamentals at nanometer scale. However, to date most super-resolution modalities require either complicated/costly purpose-built systems such as multiple-beam architectures or complex post-processing procedures with intrinsic artifacts. Achieving three-dimensional (3D) or multi-channel sub-diffraction microscopic imaging using a simple method remains a challenging and struggling task. Herein, we proposed 3D highly-nonlinear super-resolution microscopy using a single-beam excitation strategy, and the microscopy principle was modelled and studied based on the ultrahigh nonlinearity enabled by photon avalanches. According to the simulation, the point spread function of highly nonlinear microscopy is switchable among different modes and can shrink three-dimensionally to sub-diffraction scale at the photon avalanche mode. Experimentally, we demonstrated 3D optical nanoscopy assisted with huge optical nonlinearities in a simple laser scanning configuration, achieving a lateral resolution down to 58 nm (λ/14) and an axial resolution down to 185 nm (λ/5) with one single beam of low-power, continuous-wave, near-infrared laser. We further extended the photon avalanche effect to many other emitters to develop multi-color photon avalanching nanoprobes based on migrating photon avalanche mechanism, which enables us to implement single-beam dual-color sub-diffraction super-resolution microscopic imaging.

Tandem Photon Avalanches for Various Nanoscale Emitters with Optical Nonlinearity up to 41st-Order through Interfacial Energy Transfer.

Photon avalanche has received continuous attention owing to its superior nonlinear dynamics and promising advanced applications. However, its impact is limited due to the intrinsic energy levels as well as the harsh requirements for the composites and sizes of doped materials. Here, with a universal mechanism named tandem photon avalanche (TPA), giant optical nonlinear response up to 41st-order in erbium ions, one of the most important lanthanide emitters, has been achieved on the nanoscale through interfacial energy transfer process. After capturing energy directly from the avalanched energy state 3 H4 of Tm3+ (800-nm emission), erbium ions also exhibit bright green and red PA emissions with intensities comparable to that of Tm3+ at a low excitation threshold (7.1 kWcm-2 ). Using the same strategy, effective PA looping cycles are successfully activated in Ce3+ and Ho3+ . Additionally, Yb3+ -mediated networks are constructed to further propagate PA effects to lowly-doped Tm3+ , enabling 475-nm PA emission. The newly proposed TPA strategy provides a facile route for generating photon avalanche not only from erbium ions but also from various emitters in multilayered core-shell nanoparticles.

Highly water-soluble and biocompatible hyaluronic acid functionalized upconversion nanoparticles as ratiometric nanoprobes for label-free detection of nitrofuran and doxorubicin.

Antibiotic detection is crucial and challenging because the widespread consumption of antibiotics has shown extensive harmful effects on food, environment and human health. Here, we propose highly water-soluble and biocompatible hyaluronic acid (HYA) functionalized upconversion nanoparticles (UCNPs) for ratiometric detection of multiple antibiotics. The ultraviolet upconversion luminescence (UCL) from UCNPs was significantly quenched by nitrofurazone (NFZ)/nitrofurantoin (NFT), and blue UCL was quenched by doxorubicin (DOX), while red UCL remained unchanged for internal reference. The UCNPs-HYA nanoprobes exhibit excellently sensitive and selective NFZ, NFT and DOX detection in linear range of 2.5-100 µM, 2.5-80 µM, and 2.5-200 µM with the LOD at 0.28 µM (55 µg/kg), 0.20 µM (48 µg/kg) and 0.17 µM (97 µg/kg), respectively. The nanoprobes achieved detecting real samples of NFZ in lake water, liquid milk and chicken meat with satisfactory results, and UCL bioimaging of DOX in HeLa cells. The UCNPs-HYA ratiometric nanoprobes are promising for food samples detection and potential biosensing in the cellular environment.

Suppression of Cation Intermixing Highly Boosts the Performance of Core-Shell Lanthanide Upconversion Nanoparticles.

Lanthanide upconversion nanoparticles (UCNPs) have been extensively explored as biomarkers, energy transducers, and information carriers in wide-ranging applications in areas from healthcare and energy to information technology. In promoting the brightness and enriching the functionalities of UCNPs, core-shell structural engineering has been well-established as an important approach. Despite its importance, a strong limiting issue has been identified, namely, cation intermixing in the interfacial region of the synthesized core-shell nanoparticles. Currently, there still exists confusion regarding this destructive phenomenon and there is a lack of facile means to reach a delicate control of it. By means of a new set of experiments, we identify and provide in this work a comprehensive picture for the major physical mechanism of cation intermixing occurring in synthesis of core-shell UCNPs, i.e., partial or substantial core nanoparticle dissolution followed by epitaxial growth of the outer layer and ripening of the entire particle. Based on this picture, we provide an easy but effective approach to tackle this issue that enables us to produce UCNPs with highly boosted optical properties.

Upconversion nanoscopy revealing surface heterogeneity of tumor-secreted extracellular vesicles.

Super-resolution microscopic imaging employing upconversion nanoparticles is applied to reveal the surface heterogeneity of tumor cell-derived small extracellular vesicles, i.e., exosome. The number of surface antigens of every extracellular vesicles can be quantified by both the high imaging resolution and stable brightness of upconversion nanoparticles. This method proves its great potential in nanoscale biological studies.

Improving Plant Photosynthesis through Light-Harvesting Upconversion Nanoparticles.

Nanotechnology is considered as an emerging effective means to augment plant photosynthesis. However, there is still a lot of work to be done in this field. Here, we applied the upconversion nanoparticles (UCNPs) on lettuce leaves and found that the UCNPs were able to transport into the lettuce body and colocalize with the chloroplasts. It was proved that UCNPs could harvest the near-infrared light of sunlight and increase the electron transfer rate in the photosynthesis process, thus increasing the photosynthesis rate. The gene expression analysis showed that more than 90% of gene expression in photosynthesis was upregulated. After spraying the UCNP solution on the leaves of lettuce and placing the lettuce under sunlight for 1 week, the wet/dry weight of the leaves increased by 53.33% and 45.71%, respectively. This nanoengineering of light-harvesting UCNPs may have great potential for applications in agriculture.

Super-resolution microscopy enabled by high-efficiency surface-migration emission depletion.

Nonlinear depletion of fluorescence states by stimulated emission constitutes the basis of stimulated emission depletion (STED) microscopy. Despite significant efforts over the past decade, achieving super-resolution at low saturation intensities by STED remains a major technical challenge. By harnessing the surface quenching effect in NaGdF4:Yb/Tm nanocrystals, we report here high-efficiency emission depletion through surface migration. Using a dual-beam, continuous-wave laser manipulation scheme (975-nm excitation and 730-nm de-excitation), we achieved an emission depletion efficiency of over 95% and a low saturation intensity of 18.3 kW cm-2. Emission depletion by surface migration through gadolinium sublattices enables super-resolution imaging with sub-20 nm lateral resolution. Our approach circumvents the fundamental limitation of high-intensity STED microscopy, providing autofluorescence-free, re-excitation-background-free imaging with a saturation intensity over three orders of magnitude lower than conventional fluorophores. We also demonstrated super-resolution imaging of actin filaments in Hela cells labeled with 8-nm nanoparticles. Combined with the highly photostable lanthanide luminescence, surface-migration emission depletion (SMED) could provide a powerful mechanism for low-power, super-resolution imaging or biological tracking as well as super-resolved optical sensing/writing and lithography.

Photoswitching the injected energy flux via core-sensitized energy migration upconversion for emission-varying STED microscopy.

Stimulated emission depletion (STED) microscopy achieved with lanthanide-doped upconversion nanoparticles (UCNPs) exhibits many outstanding advantages such as low-power illumination, near-infrared (NIR) excitation, and high photostability. However, the available types of UCNP-STED probes are very limited and rely greatly on the specific depletion mechanism. Here, by combining the STED and the energy migration upconversion processes, emissions of Tb3+, Eu3+, Dy3+, and Sm3+ distributed in the shell can all be depleted by interrupting the injected energy flux from the Tm3+-doped core nanoparticles. With the merit of the proposed strategy, new types of UCNP-STED probes are demonstrated to perform emission-varying STED imaging with one single, fixed pair of low-power NIR continuous wave lasers.

Achieving low-power single-wavelength-pair nanoscopy with NIR-II continuous-wave laser for multi-chromatic probes.

Stimulated emission depletion (STED) microscopy is a powerful diffraction-unlimited technique for fluorescence imaging. Despite its rapid evolution, STED fundamentally suffers from high-intensity light illumination, sophisticated probe-defined laser schemes, and limited photon budget of the probes. Here, we demonstrate a versatile strategy, stimulated-emission induced excitation depletion (STExD), to deplete the emission of multi-chromatic probes using a single pair of low-power, near-infrared (NIR), continuous-wave (CW) lasers with fixed wavelengths. With the effect of cascade amplified depletion in lanthanide upconversion systems, we achieve emission inhibition for a wide range of emitters (e.g., Nd3+, Yb3+, Er3+, Ho3+, Pr3+, Eu3+, Tm3+, Gd3+, and Tb3+) by manipulating their common sensitizer, i.e., Nd3+ ions, using a 1064-nm laser. With NaYF4:Nd nanoparticles, we demonstrate an ultrahigh depletion efficiency of 99.3 ± 0.3% for the 450 nm emission with a low saturation intensity of 23.8 ± 0.4 kW cm-2. We further demonstrate nanoscopic imaging with a series of multi-chromatic nanoprobes with a lateral resolution down to 34 nm, two-color STExD imaging, and subcellular imaging of the immunolabelled actin filaments. The strategy expounded here promotes single wavelength-pair nanoscopy for multi-chromatic probes and for multi-color imaging under low-intensity-level NIR-II CW laser depletion.

Migrating photon avalanche in different emitters at the nanoscale enables 46th-order optical nonlinearity.

A photon avalanche (PA) effect that occurs in lanthanide-doped solids gives rise to a giant nonlinear response in the luminescence intensity to the excitation light intensity. As a result, much weaker lasers are needed to evoke such PAs than for other nonlinear optical processes. Photon avalanches are mostly restricted to bulk materials and conventionally rely on sophisticated excitation schemes, specific for each individual system. Here we show a universal strategy, based on a migrating photon avalanche (MPA) mechanism, to generate huge optical nonlinearities from various lanthanide emitters located in multilayer core/shell nanostructrues. The core of the MPA nanoparticle, composed of Yb3+ and Pr3+ ions, activates avalanche looping cycles, where PAs are synchronously achieved for both Yb3+ and Pr3+ ions under 852 nm laser excitation. These nanocrystals exhibit a 26th-order nonlinearity and a clear pumping threshold of 60 kW cm-2. In addition, we demonstrate that the avalanching Yb3+ ions can migrate their optical nonlinear response to other emitters (for example, Ho3+ and Tm3+) located in the outer shell layer, resulting in an even higher-order nonlinearity (up to the 46th for Tm3+) due to further cascading multiplicative effects. Our strategy therefore provides a facile route to achieve giant optical nonlinearity in different emitters. Finally, we also demonstrate applicability of MPA emitters to bioimaging, achieving a lateral resolution of ~62 nm using one low-power 852 nm continuous-wave laser beam.

Noninvasive and early diagnosis of acquired brain injury using fluorescence imaging in the NIR-II window.

Acquired brain injury (ABI), which is the umbrella term for all brain injuries, is one of the most dangerous diseases resulting in high morbidity and mortality, making it extremely significant to early diagnosis of ABI. Current methods, which are mainly composed of X-ray computed tomography and magnetic resonance angiography, remain limited in diagnosis of ABI with respect to limited spatial resolution and long scanning times. Here, we reported through-skull fluorescence imaging of mouse cerebral vasculature without craniotomy, utilizing the fluorescence of down-conversion nanoparticles (DCNPs) in the 1.3 - 1.7 µm near-infrared window (NIR-II window). Due to its high spatial resolution of 22.79 µm, the NIR-II fluorescence imaging method could quickly distinguish the brain injury region of mice after performing the stab wound injury (traumatic brain injury) and ischemic stroke (non-traumatic brain injury), enabling it a powerful tool in the noninvasive and early diagnosis of ABI.

The Spectroscopic Properties and Microscopic Imaging of Thulium-Doped Upconversion Nanoparticles Excited at Different NIR-II Light.

Lanthanide-doped upconversion nanoparticles (UCNPs) are promising bioimaging nanoprobes due to their excellent photostability. As one of the most commonly used lanthanide activators, Tm3+ ions have perfect ladder-type electron configuration and can be directly excited by bio-friendly near-infrared-II (NIR-II) wavelengths. Here, the emission characteristics of Tm3+-doped nanoparticles under laser excitations of different near-infrared-II wavelengths were systematically investigated. The 1064 nm, 1150 nm, and 1208 nm lasers are proposed to be three excitation strategies with different response spectra of Tm3+ ions. In particular, we found that 1150 nm laser excitation enables intense three-photon 475 nm emission, which is nearly 100 times stronger than that excited by 1064 nm excitation. We further optimized the luminescence brightness after investigating the luminescence quenching mechanism of bare NaYF4: Tm (1.75%) core. After growing an inert shell, a ten-fold increase of emission intensity was achieved. Combining the advantages of NIR-II wavelength and the higher-order nonlinear excitation, a promising facile excitation strategy was developed for the application of thulium-doped upconversion nanoparticles in nanoparticles imaging and cancer cell microscopic imaging.

Plant tissue imaging with bipyramidal upconversion nanocrystals by introducing Tm3+ ions as energy trapping centers.

Plant cell imaging is critical for agricultural production and plant pathology study. Advanced upconversion nanoparticles (UCNPs) are being developed as fluorescent probes for imaging cells and tissues in vivo and in vitro. Unfortunately, the thick cellulosic walls as barriers together with hemicelluloses and pectin hinder the entrance of macromolecules into the epidermal plant cell. Hence, realizing satisfactory temporal and spatial resolution with UCNPs remains an arduous task. Here, bipyramidal LiErF4:1%Tm3+@LiYF4 core-shell UCNPs with a super-bright red emission upon 980 nm laser excitation are explored, where the introduction of Tm3+ ions permits alleviation of the energy loss at defective sites and a significant improvement of the upconversion output. The as-obtained bipyramidal UCNPs could readily puncture plant cell walls and further penetrate into cell membranes, facilitating improved tissue imaging of cellular internalization, as demonstrated with the luminescence images obtained by multiphoton laser-scanning microscopy. Hence our work opens up a new avenue for exploring effective upconversion nanoparticles for achieving high resolution imaging of plant tissues.

Near-infrared light excited photodynamic anticancer therapy based on UCNP@AIEgen nanocomposite.

Photodynamic therapy (PDT), a clinically approved cancer treatment strategy, features non-invasiveness, few side-effects, high spatial resolution, etc. The advancement of PDT has been significantly restricted by the penetration depth of the excitation light. Herein, an effective fluorogen, TBD, with aggregation-induced emission characteristics (AIEgen) and high reactive-oxygen-species (ROS) generation efficiency was reported and integrated with a near infrared (NIR) light excitable upconversion nanoparticle (UCNP) to construct NIR light excitable UCNP@TBD nanocomposites. The formed nanocomposite has excellent photostability, good biocompatibility, and efficient ROS generation under NIR light excitation via Förster resonance energy transfer (FRET), enabling NIR light excited PDT. Moreover, the proposed NIR light excited PDT can break the impasse between the penetration depth and excitation volume in conventional PDT, effectively improving the anticancer therapeutic outcome. In vitro cancer cell ablation and in vivo tumor growth inhibition validated that the proposed UCNP@TBD nanocomposite is a promising NIR light excitable PDT agent with great potential for future translational research.

Binary Nanoparticle Superlattices for Plasmonically Modulating Upconversion Luminescence.

Engineering a facile and controllable approach to modulate the spectral properties of lanthanide-doped upconversion nanoparticles (UCNPs) is always an ongoing challenge. Herein, long-range ordered, distinct two-dimensional (2D) binary nanoparticle superlattices (BNSLs) composed of NaREF4 :Yb/Er (RE = Y and Gd) UCNPs and plasmonic metallic nanoparticles (Au NPs), including AB, AB3 , and AB13 lattices, are fabricated via a slow evaporation-driven self-assembly to achieve plasmonic modulation of upconversion luminescence (UCL). Optical measurements reveal that typical red-green UCL from UCNPs can be effectively modulated into reddish output in BNSLs, with a drastically shortened lifetime. Notably, for AB3 - and AB13 -type BNSLs with more proximal Au NPs around each UCNP, modified UCL with fine-structured spectral lineshape is observed. These differences could be interpreted by the interplay of collective plasmon resonance introduced by 2D periodic Au arrays and spectrally selective energy transfer between UCNPs and Au. Thus, fabricating UCNP-Au BNSLs with desired lattice parameters and NP configurations could be a promising way to tailor the UCL through controlled plasmonic modulation.