Optically Robust and Biocompatible Mechanosensitive Upconverting Nanoparticles

Surface engineering of metal-organic framework nanoparticles-based miRNA carrier: Boosting RNA stability, intracellular delivery and synergistic therapy

MicroRNAs (miRNAs) are small noncoding RNAs that are critical for the regulation of multiple physiological and pathological processes, thus holding great clinical potential. However, the therapeutic applications of miRNAs are severely limited by their biological instability and poor intracellular delivery. Herein, we describe a dual-layers surface engineering strategy to design an efficient miRNA delivery nanosystem based on metal-organic frameworks (MOFs) incorporating lipid coating. The resulting nanoparticle system was demonstrated to protect miRNA from ribonuclease degradation, enhance cellular uptake and facilitate lysosomal escape. These ensured effective miRNA mediated gene therapy, which synergized with MOF-specific photodynamic therapy and pre-encapsulated doxorubicin (Dox) chemotherapy to provide a multifunctional with therapeutic effectiveness against cencer cells The mechanisms of miRNA binding and Dox loading were revealed, demonstrating the potential of the present MOFs surface-engineered strategy to overcome their inherent pore-size restriction for macromolecular miRNA carrying, enableefficient co-delivery. In vitro studies revealed the potential of our multifunctional system for miRNA delivery and the demonstrated the therapeutic effectiveness against cancer cells, thereby providing a versatile all-in-one MOFs strategy for delivery of nucleic acids and diverse therapeutic molecules in synergistic therapy.

Advancements and applications of upconversion nanoparticles in wound dressings

Wound healing is a complex process that requires effective management to prevent infections and promote efficient tissue regeneration. In recent years, upconversion nanoparticles (UCNPs) have emerged as promising materials for wound dressing applications due to their unique optical properties and potential therapeutic functionalities. These nanoparticles possess enhanced antibacterial properties when functionalized with antibacterial agents, helping to prevent infections, a common complication in wound healing. They can serve as carriers for controlled drug delivery, enabling targeted release of therapeutic agents to the wound site, allowing for tailored treatment and optimal healing conditions. These nanoparticles possess the ability to convert near-infrared (NIR) light into the visible and/or ultraviolet (UV) regions, making them suitable for therapeutic (photothermal therapy and photodynamic therapy) and diagnostic applications. In the context of wound healing, these nanoparticles can be combined with other materials such as hydrogels, fibers, metal-organic frameworks (MOFs), graphene oxide, etc., to enhance the healing process and prevent the growth of microbial infections. Notably, UCNPs can act as sensors for real-time monitoring of the wound healing progress, providing valuable feedback to healthcare professionals. Despite their potential, the use of UCNPs in wound dressing applications faces several challenges. Ensuring the stability and biocompatibility of UCNPs under physiological conditions is crucial for their effective integration into dressings. Comprehensive safety and efficacy evaluations are necessary to understand potential risks and optimize UCNP-based dressings. Scalability and cost-effectiveness of UCNP synthesis and manufacturing processes are important considerations for practical applications. In addition, efficient incorporation of UCNPs into dressings, achieving uniform distribution, poses an important challenge that needs to be addressed. Future research should prioritize addressing concerns regarding stability and biocompatibility, efficient integration into dressings, rigorous safety evaluation, scalability, and cost-effectiveness. The purpose of this review is to critically evaluate the advantages, challenges, and key properties of UCNPs in wound dressing applications to provide insights into their potential as innovative solutions for enhancing wound healing outcomes. We have provided a detailed description of various types of smart wound dressings, focusing on the synthesis and biomedical applications of UCNPs, specifically their utilization in different types of wound dressings.

Blastopore gating mechanism to regulate extracellular fluid excretion

Fluid uptake and efflux play roles in early embryogenesis as well as in adult homeostasis. Multicellular organisms have two main pathways for fluid movement: cellular-level, such as transcellular and paracellular pathways, and tissue-level, involving muscle contraction. Interestingly, early Xenopus embryos with immature functional muscles excrete archenteron fluid via a tissue-level mechanism that opens the blastopore through a gating mechanism that is unclear. Using microelectrodes, we show that the archenteron has a constant fluid pressure and as development progress the blastopore pressure resistance decreases. Combining physical perturbations and imaging analyses, we found that the pushing force exerted by the circumblastoporal collars (CBCs) at the slit periphery regulates pressure resistance. We show that apical constriction at the blastopore dorsoventral ends contributes to this pushing force, and relaxation of ventral constriction causes fluid excretion. These results indicate that actomyosin contraction mediates temporal control of tissue-level blastopore opening and fluid excretion in early Xenopus embryos.

Self-Assembly of Selenium-Doped Carbon Quantum Dots as Antioxidants for Hepatic Ischemia-Reperfusion Injury Management

Hepatic ischemia-reperfusion injury (HIRI) is a critical complication after liver surgery that negatively affects surgical outcomes of patients with the end-stage liver-related disease. Reactive oxygen species (ROS) are responsible for the development of ischemia-reperfusion injury and eventually lead to hepatic dysfunction. Selenium-doped carbon quantum dots (Se-CQDs) with an excellent redox-responsive property can effectively scavenge ROS and protect cells from oxidation. However, the accumulation of Se-CQDs in the liver is extremely low. To address this concern, the fabrication of Se-CQDs-lecithin nanoparticles (Se-LEC NPs) is developed through self-assembly mainly driven by the noncovalent interactions. Lecithin acting as the self-assembly building block also makes a pivotal contribution to the therapeutic performance of Se-LEC NPs due to its capability to react with ROS. The fabricated Se-LEC NPs largely accumulate in the liver, effectively scavenge ROS and inhibit the release of inflammatory cytokines, thus exerting beneficial therapeutic efficacy on HIRI. This work may open a new avenue for the design of self-assembled Se-CQDs NPs for the treatment of HIRI and other ROS-related diseases.

Nanocarrier design–function relationship: The prodigious role of properties in regulating biocompatibility for drug delivery applications

The concept of drug delivery systems as a magic bullet for the delivery of bioactive compounds has emerged as a promising approach in the treatment of different diseases with significant advantages over the limitations of traditional methods. While nanocarrier-based drug delivery systems are the main advocates of drug uptake because they offer several advantages including reduced non-specific biodistribution, improved accumulation, and enhanced therapeutic efficiency; their safety and biocompatibility within cellular/tissue systems are therefore important for achieving the desired effect. The underlying power of "design-interplay chemistry" in modulating the properties and biocompatibility at the nanoscale level will direct the interaction with their immediate surrounding. Apart from improving the existing nanoparticle physicochemical properties, the balancing of the hosts' blood components interaction holds the prospect of conferring newer functions altogether. So far, this concept has been remarkable in achieving many fascinating feats in addressing many challenges in nanomedicine such as immune responses, inflammation, biospecific targeting and treatment, and so on. This review, therefore, provides a diverse account of the recent advances in the fabrication of biocompatible nano-drug delivery platforms for chemotherapeutic applications, as well as combination therapy, theragnostic, and other diseases that are of interest to scientists in the pharmaceutical industries. Thus, careful consideration of the "property of choice" would be an ideal way to realize specific functions from a set of delivery platforms. Looking ahead, there is an enormous prospect for nanoparticle properties in regulating biocompatibility.

Nanocomposite Hydrogels as Functional Extracellular Matrices

Over recent years, nano-engineered materials have become an important component of artificial extracellular matrices. On one hand, these materials enable static enhancement of the bulk properties of cell scaffolds, for instance, they can alter mechanical properties or electrical conductivity, in order to better mimic the in vivo cell environment. Yet, many nanomaterials also exhibit dynamic, remotely tunable optical, electrical, magnetic, or acoustic properties, and therefore, can be used to non-invasively deliver localized, dynamic stimuli to cells cultured in artificial ECMs in three dimensions. Vice versa, the same, functional nanomaterials, can also report changing environmental conditions-whether or not, as a result of a dynamically applied stimulus-and as such provide means for wireless, long-term monitoring of the cell status inside the culture. In this review article, we present an overview of the technological advances regarding the incorporation of functional nanomaterials in artificial extracellular matrices, highlighting both passive and dynamically tunable nano-engineered components.

Engineering Bright and Mechanosensitive Alkaline-Earth Rare-Earth Upconverting Nanoparticles

Upconverting nanoparticles (UCNPs) are an emerging platform for mechanical force sensing at the nanometer scale. An outstanding challenge in realizing nanometer-scale mechano-sensitive UCNPs is maintaining a high mechanical force responsivity in conjunction with bright optical emission. This Letter reports mechano-sensing UCNPs based on the lanthanide dopants Yb³⁺ and Er³⁺, which exhibit a strong ratiometric change in emission spectra and bright emission under applied pressure. We synthesize and analyze the pressure response of five different types of nanoparticles, including cubic NaYF₄ host nanoparticles and alkaline-earth host materials CaLuF, SrLuF, SrYbF, and BaLuF, all with lengths of 15 nm or less. By combining optical spectroscopy in a diamond anvil cell with single-particle brightness, we determine the noise equivalent sensitivity (GPa/√Hz) of these particles. The SrYb_0.72Er_0.28F@SrLuF particles exhibit an optimum noise equivalent sensitivity of 0.26 ± 0.04 GPa/√Hz. These particles present the possibility of robust nanometer-scale mechano-sensing.

Degradation of upconverting nanoparticles in simulated fluids evaluated by ratiometric luminescence

The effect of artificially simulated fluids on the optical properties of upconversion nanoparticles and the degradation mechanism was systematically studied.

Exploiting the upconversion luminescence, Lewis acid catalytic and photothermal properties of lanthanide-based nanomaterials for chemical and polymerization reactions

Lanthanide-based nanocrystals possess three unique physical properties that make them attractive for facilitating photoreactions, namely photon upconversion, Lewis acid catalytic activity and photothermal effect. When co-doped with suitable sensitizer and...

Responsive Sensors of Upconversion Nanoparticles

Upconversion nanoparticles are a class of luminescent materials that convert longer-wavelength near-infrared photons into visible and ultraviolet emissions. They can respond to various external stimuli, which underpins many opportunities for developing the next generation of sensing technologies. In this perspective, the unique stimuli-responsive properties of upconverting nanoparticles are introduced, and their recent implementations in sensing are summarized. Promising material development strategies for enhancing the key sensing merits, including intrinsic sensitivity, biocompatibility and modality, are identified and discussed. The outlooks on future technological developments, novel sensing concepts, and applications of nanoscale upconversion sensors are provided.

A nanosized anionic MOF with rich thiadiazole groups for controlled oral drug delivery

Controlling the crystal size and surface chemistry of MOF materials, and understanding their multifunctional effect are of great significance for the biomedical applications of MOF systems. Herein, we designed and synthesized a new anionic MOF, ZJU-64-NSN, which features 1D channels decorated with highly polarized thiadiazole groups, and its crystal size could be systematically tuned from 200 ​μm to 300 ​nm through a green and simple approach. As a result, the optimal nanosized ZJU-64-NSN is found to enable an ultrafast loading of cationic drug procainamide (PA) (21.2 ​wt% within 1 ​min). Moreover, the undesirable chemical stability of PA@ZJU-64-NSN is greatly improved by the surface coating of polyethylene glycol (PEG) biopolymer. The final drug delivery system PEG/PA@ZJU-64-NSN is found to effectively prevent PA from premature release under the harsh stomach environments due to the intense host-guest interaction, and mainly release PA to the targeted intestinal surroundings. Such controlled drug delivery is proved to be triggered by endogenic Na⁺ ions instead of H⁺ ions, well revealed by the study on the dynamics behavior of drug release and UV–Vis absorption spectrum. Good biocompatibility of ZJU-64-NSN and PEG-coated ZJU-64-NSN has been fully demonstrated by MTT assay as well as confocal microscopy imaging.

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A new anionic MOF enables an ultrafast drug loading.

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The crystal size of such MOF could be well size-controlled.

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The surface coating of PEG improves the chemical stability of drug carrier.

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The drug delivery system reveals an endogenic Na ​⁺ ​-triggered procainamide release.

Local Structure Engineering in Lanthanide-Doped Nanocrystals for Tunable Upconversion Emissions

Upconversion emissions from lanthanide-doped nanocrystals have sparked extensive research interests in nanophotonics, biomedicine, photovoltaics, photocatalysis, etc. Rational modulation of upconversion emissions is highly desirable to meet the requirements of specific applications. Among the diverse developed methods, local structure engineering is fundamentally feasible, through which the upconversion emission intensity, selectivity, wavelength shift, and lifetime can be tuned effectively. The underlying mechanism of the local-structure-dependent upconversion emissions lies in the degree of parity hybridization and energy level splitting of lanthanide ions as well as the interionic energy transfer efficiency. Over the past few years, there has been significant progress in local-structure-engineered upconversion emissions. In this Perspective, we first introduce the principles of upconversion emissions and typical characterization methods for local structure. Subsequently, we summarize recent achievements in tuning of upconversion emissions through local structure engineering, including host composition adjustment, external field regulation, and interfacial strain management. Finally, we propose a few perspectives that should tackle the current bottlenecks. This Perspective is expected to deepen the understanding of local-structure-dependent upconversion emissions and arouse adequate attention to the engineering of local structure for desired properties of inorganic nanocrystals.

Near infrared bioimaging and biosensing with semiconductor and rare-earth nanoparticles: recent developments in multifunctional nanomaterials

Research in novel materials has been extremely active over the past few decades, wherein a major area of interest has been nanoparticles with special optical properties. These structures can overcome some of the intrinsic limitations of contrast agents routinely used in medical practice, while offering additional functionalities. Materials that absorb or scatter near infrared light, to which biological tissues are partially transparent, have attracted significant attention and demonstrated their potential in preclinical research. In this review, we provide an at-a-glance overview of the most recent developments in near infrared nanoparticles that could have far-reaching applications in the life sciences. We focus on materials that offer additional functionalities besides diagnosis based on optical contrast: multiple imaging modalities (multimodal imaging), sensing of physical and chemical cues (multivariate diagnosis), or therapeutic activity (theranostics). Besides presenting relevant case studies for each class of optically active materials, we discuss their design and safety considerations, detailing the potential hurdles that may complicate their clinical translation. While multifunctional nanomaterials have shown promise in preclinical research, the field is still in its infancy; there is plenty of room to maximize its impact in preclinical studies as well as to deliver it to the clinics.

Time for NanoNeuro

The study of electronic properties of materials at the nanoscale has unveiled physical laws and generated materials such as nanoparticles, quantum dots, nanodiamonds, nanoelectrodes, and nanoprobes. Independently, large-scale public and private neuroscience programs have been launched to develop methods to measure and manipulate neural circuits in living animals and humans. Here, we review an upcoming field, NanoNeuro, defined as the intersection of nanoscience and neuroscience, that aims to develop nanoscale methods to record and stimulate neuronal activity. Because of their unique physical properties, nanomaterials have intrinsic advantages as biosensors and actuators, and they may be applicable to humans without the need for genetic modifications. Thus, nanoscience could make major methodological contributions to the future of neuroscience and, more generally, to biomedical sciences.

Ex vivo interaction study of NaYF4 :Yb,Er nanophosphors with isolated mitochondria

Ex vivo interaction of NaYF₄ :Yb,Er nanophosphors with isolated mitochondria has been investigated. The nanophosphors were synthesized using the hydrothermal method. The synthesized NaYF₄ :Yb,Er nanophosphors were characterized for physicochemical properties. The NaYF₄ :Yb,Er nanophosphors showed successful upconversion with excitation wavelength lying in the near-infrared region. The effect of synthesized NaYF₄ :Yb,Er nanophosphors on mitochondria isolated from the chicken heart tissue was examined through ROS generation capacity, membrane fluidity, and complex II activity. The exposer of NaYF₄ :Yb,Er nanophosphors to isolated mitochondria inhibits ROS generation activity as compared to control. The mitochondria membrane fluidity of the lipid bilayer and complex-II activity of mitochondria was observed to be unaltered after the interaction with NaYF₄ :Yb,Er nanoparticles. The results confirm that synthesized NaYF₄ :Yb,Er nanoparticles can be used as a safe contrast agent.

X-ray-Based Techniques to Study the Nano-Bio Interface

X-ray-based analytics are routinely applied in many fields, including physics, chemistry, materials science, and engineering. The full potential of such techniques in the life sciences and medicine, however, has not yet been fully exploited. We highlight current and upcoming advances in this direction. We describe different X-ray-based methodologies (including those performed at synchrotron light sources and X-ray free-electron lasers) and their potentials for application to investigate the nano-bio interface. The discussion is predominantly guided by asking how such methods could better help to understand and to improve nanoparticle-based drug delivery, though the concepts also apply to nano-bio interactions in general. We discuss current limitations and how they might be overcome, particularly for future use in vivo.

Desilylation Induced by Metal Fluoride Nanocrystals Enables Cleavage Chemistry In Vivo

Metal fluoride nanocrystals are widely used in biomedical studies owing to their unique physicochemical properties. The release of metal ions and fluorides from nanocrystals is intrinsic due to the solubility equilibrium. It used to be considered as a drawback because it is related to the decomposition and defunction of metal fluoride nanocrystals. Many strategies have been developed to stabilize the nanocrystals, and the equilibrium concentrations of fluoride are often <1 mM. Here we make good use of this minimum amount of fluoride and unveil that metal fluoride nanocrystals could effectively induce desilylation cleavage chemistry, enabling controlled release of fluorophores and drug molecules in test tubes, living cells, and tumor-bearing mice. Biocompatible PEG (polyethylene glycol)-coated CaF₂ nanocrystals have been prepared to assay the efficiency of desilylation-induced controlled release of functional molecules. We apply the strategy to a prodrug activation of monomethyl auristatin E (MMAE), showing a remarkable anticancer effect, while side effects are almost negligible. In conclusion, this desilylation-induced cleavage chemistry avails the drawback on empowering metal fluoride nanocrystals with a new function of perturbing or activating for further biological applications.

Lanthanide-Based Nanosensors: Refining Nanoparticle Responsiveness for Single Particle Imaging of Stimuli

Lanthanide nanoparticles (LNPs) are promising sensors of chemical, mechanical, and temperature changes; they combine the narrow-spectral emission and long-lived excited states of individual lanthanide ions with the high spatial resolution and controlled energy transfer of nanocrystalline architectures. Despite considerable progress in optimizing LNP brightness and responsiveness for dynamic sensing, detection of stimuli with a spatial resolution approaching that of individual nanoparticles remains an outstanding challenge. Here, we highlight the existing capabilities and outstanding challenges of LNP sensors, en-route to nanometer-scale, single particle sensor resolution. First, we summarize LNP sensor read-outs, including changes in emission wavelength, lifetime, intensity, and spectral ratiometric values that arise from modified energy transfer networks within nanoparticles. Then, we describe the origins of LNP sensor imprecision, including sensitivity to competing conditions, interparticle heterogeneities, such as the concentration and distribution of dopant ions, and measurement noise. Motivated by these sources of signal variance, we describe synthesis characterization feedback loops to inform and improve sensor precision, and introduce noise-equivalent sensitivity as a figure of merit of LNP sensors. Finally, we project the magnitudes of chemical and pressure stimulus resolution achievable with single LNPs at nanoscale resolution. Our perspective provides a roadmap for translating ensemble LNP sensing capabilities to the single particle level, enabling nanometer-scale sensing in biology, medicine, and sustainability.

Giant nonlinear optical responses from photon-avalanching nanoparticles

Avalanche phenomena use steeply nonlinear dynamics to generate disproportionately large responses from small perturbations, and are found in a multitude of events and materials¹. Photon avalanching enables technologies such as optical phase-conjugate imaging², infrared quantum counting³ and efficient upconverted lasing^4-6. However, the photon-avalanching mechanism underlying these optical applications has been observed only in bulk materials and aggregates^6,7, limiting its utility and impact. Here we report the realization of photon avalanching at room temperature in single nanostructures-small, Tm³⁺-doped upconverting nanocrystals-and demonstrate their use in super-resolution imaging in near-infrared spectral windows of maximal biological transparency. Avalanching nanoparticles (ANPs) can be pumped by continuous-wave lasers, and exhibit all of the defining features of photon avalanching, including clear excitation-power thresholds, exceptionally long rise time at threshold, and a dominant excited-state absorption that is more than 10,000 times larger than ground-state absorption. Beyond the avalanching threshold, ANP emission scales nonlinearly with the 26th power of the pump intensity, owing to induced positive optical feedback in each nanocrystal. This enables the experimental realization of photon-avalanche single-beam super-resolution imaging⁷ with sub-70-nanometre spatial resolution, achieved by using only simple scanning confocal microscopy and without any computational analysis. Pairing their steep nonlinearity with existing super-resolution techniques and computational methods^8-10, ANPs enable imaging with higher resolution and at excitation intensities about 100 times lower than other probes. The low photon-avalanching threshold and excellent photostability of ANPs also suggest their utility in a diverse array of applications, including sub-wavelength imaging^7,11,12 and optical and environmental sensing^13-15.

Water dispersible ligand-free rare earth fluoride nanoparticles: water transfer versus NaREF4-to-REF3 phase transformation

The chemical stability of oleate-capped sub-10 nm α- and β-NaREF4 NPs (RE = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu for α- and RE = Pr, Nd, Sm, Eu, Gd, Tb, Dy for β-phase NPs) was evaluated under the acidic conditions used for ligand removal towards water dispersibility. It was found that for such small NPs, a pH lower than 3 was necessary for the water transfer to be efficient and to yield well-dispersed ligand-free NPs. In stark contrast to the generally considered good chemical stability of NaREF4, these conditions were observed to pose a risk to phase transformation of the NaREF4 NPs into much larger, hexagonal- or orthorhombic-phase REF3, depending on the NP composition. A correlation between the thermodynamic stability of the α/β-NaREF4 and the hexagonal/orthorhombic REF3 phases - dictated by the RE ion choice - and the chemical stability of the NPs was found. For instance, β-NaGdF4 NPs remained stable, while α-NaGdF4 NPs underwent phase transformation into hexagonal GdF3. More general, NaREF4 NPs based on lighter RE ions were more prone towards phase transformation, while those based on heavier RE ions exhibited stability. Herein, within the RE series, the borderline for phase transformation was identified as Tb/Dy for α-NaREF4 NPs and Sm/Eu for β-NaREF4 NPs, respectively. Also, given the large interest in luminescent NPs for, e.g. biomedical applications, optically active Ln3+ ions (Ln = Nd, Eu, Tb, Er/Yb) were doped into α/β-NaGdF4 host NPs, and the dopant influence on the chemical stability was evaluated. Steady state and time-resolved spectroscopy unveiled spectral features characteristic for Ln3+ f-f transitions, i.e. downshifting and upconversion, before and after ligand removal. Overall, the results herein described emphasise the importance of minding the chemical procedure used for ligand removal of NaREF4 NPs of different crystalline phases and RE compositions.

Nanorods with multidimensional optical information beyond the diffraction limit

Precise design and fabrication of heterogeneous nanostructures will enable nanoscale devices to integrate multiple desirable functionalities. But due to the diffraction limit (~200 nm), the optical uniformity and diversity within the heterogeneous functional nanostructures are hardly controlled and characterized. Here, we report a set of heterogeneous nanorods; each optically active section has its unique nonlinear response to donut-shaped illumination, so that one can discern each section with super-resolution. To achieve this, we first realize an approach of highly controlled epitaxial growth and produce a range of heterogeneous structures. Each section along the nanorod structure displays tunable upconversion emissions, in four optical dimensions, including color, lifetime, excitation wavelength, and power dependency. Moreover, we demonstrate a 210 nm single nanorod as an extremely small polychromatic light source for the on-demand generation of RGB photonic emissions. This work benchmarks our ability toward the full control of sub-diffraction-limit optical diversities of single heterogeneous nanoparticles.

Development of functional nanostructures can enable a range of applications in imaging and nanoscale science. Here, the authors fabricate and characterize complex heterogeneous nanorods with diverse, tunable sub-wavelength structures.

Up-Conversion Luminescent Nanoparticles for Molecular Imaging, Cancer Diagnosis and Treatment

In the past few years, we have witnessed great development and application potential of various up-conversion luminescent nanoparticles (UCNPs) in the nanomedicine field. Based on the unique luminescent mechanism of UCNPs and the distinguishable features of cancer biomarkers and the microenvironment, an increasing number of smart UCNPs nanoprobes have been designed and widely applied to molecular imaging, cancer diagnosis, and treatment. Considerable technological success has been achieved, but the main obstacles to oncology nanomedicine is becoming an incomplete understanding of nano-bio interactions, the challenges regarding chemistry manufacturing and controls required for clinical translation and so on. This review highlights the progress of the design principles, synthesis and surface functionalization preparation, underlying applications and challenges of UCNPs-based probes for cancer bioimaging, diagnosis and treatment that capitalize on our growing understanding of tumor biology and smart nano-devices for accelerating the commercialization of UCNPs.

Spectral characterization of LiYbF4 upconverting nanoparticles

In light of the recent developments on Yb³⁺-based upconverting rare-earth nanoparticles (RENPs), we have systematically explored the spectral features of LiYbF₄:RE³⁺/LiYF₄ core/shell RENPs doped with various amounts of Tm³⁺, Er³⁺, or Ho³⁺. Tm³⁺-RENPs displayed photoluminescence from the UV to near-infrared (NIR), and the dominant high-photon-order upconversion emission of these RENPs was tunable by Tm³⁺ doping. Similarly, Er³⁺- and Ho³⁺-RENPs with green and red upconversion showed wide color tuning, depending on the doping amount and excitation power density. From steady-state power plot and photoluminescence decay studies we have observed respective changes in upconversion photon order and average lifetime that attest to a number of cross-relaxation processes occurring at higher RE³⁺ doping concentration. Particularly in the case of Tm³⁺-RENPs, cross-relaxation promotes four- and five-photon order upconversion emission in the UV and blue spectral regions. The quantum yield of high-order upconversion emission was on par with classic Yb³⁺/Tm³⁺-doped systems, yet due to the high number of sensitizer ions in the LiYbF₄ host these RENPs are expected to be brighter and thus better suited for applications such as controlled drug delivery or optogenetics. Overall, LiYbF₄:RE³⁺/LiYF₄ RENPs are promising systems to effectively generate high-order upconversion emissions, owing to excitation energy confinement within the Yb³⁺ network and its efficient funneling to the activator dopants.

Integration of luminal pressure and signalling in tissue self-organization

Many developmental processes involve the emergence of intercellular fluid-filled lumina. This process of luminogenesis results in a build up of hydrostatic pressure and signalling molecules in the lumen. However, the potential roles of lumina in cellular functions, tissue morphogenesis and patterning have yet to be fully explored. In this Review, we discuss recent findings that describe how pressurized fluid expansion can provide both mechanical and biochemical cues to influence cell proliferation, migration and differentiation. We also review emerging techniques that allow for precise quantification of fluid pressure in vivo and in situ. Finally, we discuss the intricate interplay between luminogenesis, tissue mechanics and signalling, which provide a new dimension for understanding the principles governing tissue self-organization in embryonic development.