Modularly Assembled Upconversion Nanoparticles for Orthogonally Controlled Cell Imaging and Drug Delivery

A Systematic Review of Toxicity, Biodistribution, and Biosafety in Upconversion Nanomaterials: Critical Insights into Toxicity Mitigation Strategies and Future Directions for Safe Applications

Upconversion nanoparticles (UCNPs) are emerging as highly promising nanomaterials due to their exceptional optical properties, enabling diverse applications in biosensing, bioimaging, photodynamic therapy, and drug delivery. However, their potential toxicity should be comprehensively investigated for the safe utilization of UCNPs in several biomedical and environmental applications. This review systematically evaluates the current knowledge on UCNP toxicity from 2008 to 2024, focusing on key toxicological pathways, such as oxidative stress, reactive oxygen species (ROS) production, inflammatory responses, and apoptosis/necrosis, alongside their absorption, distribution, metabolism, and excretion processes and kinetics. Distinctively, this review introduces a bibliometric analysis of UCNP toxicity and biodistribution research, providing a quantitative assessment of publication trends, influential authors, leading institutions, funding agencies, and keyword occurrences. This approach offers a macroscopic perspective on the evolution and current landscape of UCNP safety research, a dimension largely unexplored in existing literature. Furthermore, the review combines mechanistic insights into UCNP toxicity with a critical evaluation of surface modifications, physicochemical properties, and administration routes, presenting a holistic framework for understanding UCNP biosafety. By combining bibliometric data with mechanistic insights, this review provides a data-driven perspective on UCNP-associated risks, actionable strategies for enhancing biosafety through surface engineering, and a forward-looking discussion on regulatory challenges and future directions for UCNP-based technologies. These findings bridge existing gaps in the literature and offer a comprehensive resource for researchers, clinicians, and policymakers, facilitating the safe development and utilization of UCNP-based technologies while establishing robust safety guidelines to mitigate adverse effects on human health and the environment.

Upconversion-Based Photodynamic Therapy for Psoriatic Dermatitis

Psoriasis, with a global incidence rate of 2%-3%, afflicts patients with persistent erythema and scales and is often accompanied by comorbidities such as arthritis and depression, significantly impairing their quality of life. While emerging biologics and traditional medications as well as phototherapy have made certain progress in treating psoriasis, these therapies are hindered by significant drawbacks including high costs, suboptimal efficacy, and significant side effects. Photodynamic therapy (PDT) has great potential for psoriasis treatment, but its application is limited due to the weak penetration of short-wavelength light used for active photosensitizer (PS). Upconversion nanoparticles (UCNPs) offer a promising solution for traditional PDT as they could be excited by near-infrared (NIR) light to emit UV-visible light for reactive oxygen species generation, which effectively addresses penetration challenges. In this study, PS (ZnPc) was encapsulated on UCNPs coated with a porous silica shell (UCNPs-ZnPc). When topically applied to psoriatic mice skin, UCNPs-ZnPc was taken up by macrophages. Upon activation with 980 nm NIR light, psoriatic dermatitis was treated since the macrophage viability was reduced, and the overproliferation of psoriatic skin cells was suppressed. These results highlight the potential of UCNPs-mediated PDT as an innovative approach to managing psoriasis.

NIR-activated multifunctional agents for the combined application in cancer imaging and therapy

Anticancer therapies that combine both diagnostic and therapeutic capabilities hold significant promise for enhancing treatment efficacy and patient outcomes. Among these, agents responsive to near-infrared (NIR) photons are of particular interest due to their negligible toxicity and multifunctionality. These compounds are not only effective in photodynamic therapy (PDT), but also serve as contrast agents in various imaging modalities, including fluorescence and photoacoustic imaging. In this review, we explore the photophysical and photochemical properties of NIR-activated porphyrin, cyanine, and phthalocyanines derivatives as well as aggregation-induced emission compounds, highlighting their application in synergistic detection, diagnosis, and therapy. Special attention is given to the design and optimization of these agents to achieve high photostability, efficient NIR absorption, and significant yields of fluorescence, heat, or reactive oxygen species (ROS) generation depending on the application. Additionally, we discuss the incorporation of these compounds into nanocarriers to enhance their solubility, stability, and target specificity. Such nanoparticle-based systems exhibit improved pharmacokinetics and pharmacodynamics, facilitating more effective tumor targeting and broadening the application range to photoacoustic imaging and photothermal therapy. Furthermore, we summarize the application of these NIR-responsive agents in multimodal imaging techniques, which combine the advantages of fluorescence and photoacoustic imaging to provide comprehensive diagnostic information. Finally, we address the current challenges and limitations of photodiagnosis and phototherapy and highlight some critical barriers to their clinical implementation. These include issues related to their phototoxicity, limited tissue penetration, and potential off-target effects. The review concludes by highlighting future research directions aimed at overcoming these obstacles, with a focus on the development of next-generation agents and platforms that offer enhanced therapeutic efficacy and imaging capabilities in the field of cancer treatment.

Multi-Wavelength Excitable Multicolor Upconversion and Ratiometric Luminescence Thermometry of Yb3+/Er3+ Co-Doped NaYGeO4 Microcrystals

Excitation wavelength controllable lanthanide upconversion allows for real-time manipulation of luminescent color in a composition-fixed material, which has been proven to be conducive to a variety of applications, such as optical anti-counterfeiting and information security. However, current available materials highly rely on the elaborate core-shell structure in order to ensure efficient excitation-dependent energy transfer routes. Herein, multicolor upconversion luminescence in response to both near-infrared I and near-infrared II (NIR-I and NIR-II) excitations is realized in a novel but simple NaYGeO4:Yb3+/Er3+ phosphor. The remarkably enhanced red emission ratio under 1532 nm excitation, compared with that under 980 nm excitation, could be attributed to the Yb3+-mediated cross-relaxation energy transfers. Moreover, multi-wavelength excitable temperature-dependent (295-823 K) upconversion luminescence realizes a ratiometric thermometry relying on the thermally coupled levels (TCLs) of Er3+. Detailed investigations demonstrate that changing excitation wavelength makes little difference for the performances of TCL-based ratiometric thermometry of NaYGeO4:Yb3+/Er3+. These findings gain more insights to manipulate cross-relaxations for excitation controllable upconversion in single activator doped materials and benefit the cognition of the effect of excitation wavelength on ratiometric luminescence thermometry.

The Art of Nanoparticle Design: Unconventional Morphologies for Advancing Luminescent Technologies

The advanced design of rare-earth-doped (RE-doped) fluoride nanoparticles has expanded their applications ranging from anticounterfeiting luminescence and contactless temperature measurement to photodynamic therapy. Several recent studies have focused on developing rare morphologies of RE-doped nanoparticles. Distinct physical morphologies of RE-doped fluoride materials set them apart from contemporary nanoparticles. Every unusual structure holds the potential to dramatically improve the physical performance of nanoparticles, resulting in a remarkable revolution and a wide range of applications. This comprehensive review serves as a guide offering insights into various uniquely structured nanoparticles, including hollow, dumbbell-shaped, and peasecod-like forms. It aims to cater to both novices and experts interested in exploring the morphological transformations of nanoparticles. Discovering new energy transfer pathways and enhancing the optical application performance have been long-term challenges for which new solutions can be found in old papers. In the future, nanoparticle morphology design is expected to involve more refined microphysical methods and chemically-induced syntheses. Targeted modification of nanoparticle morphology and the aggregation of nanoparticles of various shapes can provide the advantages of different structures and enhance the universality of nanoparticles.

Therapeutic Applications of Nanomedicine: Recent Developments and Future Perspectives

The concept of nanomedicine has evolved significantly in recent decades, leveraging the unique phenomenon known as the enhanced permeability and retention (EPR) effect. This has facilitated major advancements in targeted drug delivery, imaging, and individualized therapy through the integration of nanotechnology principles into medicine. Numerous nanomedicines have been developed and applied for disease treatment, with a particular focus on cancer therapy. Recently, nanomedicine has been utilized in various advanced fields, including diagnosis, vaccines, immunotherapy, gene delivery, and tissue engineering. Multifunctional nanomedicines facilitate concurrent medication delivery, therapeutic monitoring, and imaging, allowing for immediate responses and personalized treatment plans. This review concerns the major advancement of nanomaterials and their potential applications in the biological and medical fields. Along with this, we also mention the various clinical translations of nanomedicine and the major challenges that nanomedicine is currently facing to overcome the clinical translation barrier.

Salinomycin and IR780-loaded upconversion nanoparticles influence biological behavior of liver cancer stem cells by persistently activating the MAPK signaling pathway

The combination of chemotherapy and phototherapy has emerged as a promising therapeutic approach for enhancing the efficacy of cancer treatment and mitigating drug resistance. Salinomycin (SAL), a polyether antibiotic, exhibits potent cytotoxicity against chemotherapy-resistant cancer cells. IR780 iodide, a novel photosensitive reagent with excellent near-infrared (NIR) light absorption and photothermal conversion abilities, is suitable for use in photothermal therapy for cancers. However, both SAL and IR780 exhibit hydrophobic properties that limit their clinical applicability. Upconversion nanoparticles (UCNPs) are an emerging class of fluorescent probe materials capable of emitting high-energy photons upon excitation by low-energy NIR light. The UCNPs not only function as nanocarriers for drug delivery but also serve as light transducers to activate photosensitizers for deep-tissue photodynamic therapy. Here, to enhance the targeting and bioavailability of hydrophobic drugs in liver cancer stem cells (LCSCs), we employ distearoyl phosphorethanolamine-polyethylene glycol (DSPE-PEG) to encapsulate SAL and IR780 on the surface of UCNPs. Cell viability was evaluated using the CCK-8 assay. Cell migration was assessed by the Transwell Boyden Chamber. The activation of the mitogen-activated protein kinase (MAPK) signaling pathway was measured via western blot. The results demonstrated successful loading of both IR780 and SAL onto the UCNPs, and the SAL and IR780-loaded UCNPs (UISP) exhibited a robust photothermal effect under NIR light irradiation. The UISP effectively inhibited the viability of HCCLM3 and LCSCs. Under NIR light irradiation, the UISP further suppressed HCCLM3 viability but had no impact on LCSC viability; however, it could further inhibit LCSC migration. Meanwhile, under NIR light irradiation, the UISP persistently activated the MAPK pathway more significantly in LCSCs. These findings suggest that exposure to NIR light results in persistent activation of the MAPK pathway by UISP, thereby influencing the biological behavior of LCSCs and enhancing their therapeutic efficacy against liver cancer.

Photoswitchable upconversion nanoparticles with excitation-dependent emission for programmed stepwise NIR phototherapy

Programmable control over therapeutic processes in phototherapy, like photodynamic therapy (PDT), is promising but challenging. This study uses an energy segmentation-based strategy to synthesize core-multi-shell upconversion nanoparticles (UCNPs), which can release three different colors (red, green, and blue) upon exposure to different near-infrared light (1550 nm, 808 nm, and 980 nm). By combining these UCNPs with photosensitizers and nitric oxide (NO) donors, a smart "off-on" PDT nanoplatform is developed. UCNPs enable independent activation of imaging, release of NO, and generation of reactive oxygen species using specific light wavelengths. The results show that sequential NO release before PDT can greatly alleviate tumor hypoxia by reducing oxygen consumption. This stepwise approach shows potential for precise NIR light-activated and imaging-guided phototherapy.

Awakening Allies for Breaking Microenvironment Barriers: NIR-II Guided Orthogonal Activation of Tumor-Infiltrating Mast Cells for Efficient Nano-Drug Delivery

Mast cells (MCs), powerful immune cells that heavily infiltrate cancer cells, play a crucial role in tumor formation. Activated MCs can release histamine and a family of proteases through degranulation effects, concurrently achieving endothelial junction weakening and stromal degradation of the tumor microenvironment, thereby clearing the obstacles for nano-drug infiltration. To achieve precise activation of tumor-infiltrating MCs, orthogonally excited rare earth nanoparticles (ORENP), with two channels, are introduced for the controllable stimulating drugs release wrapped in "photocut tape". The ORENP can emit near-infrared II (NIR-II) for image tracing for tumor localization in Channel 1 (808/NIR-II) and allows energy upconversion to emit ultraviolet (UV) light for releasing drugs for MCs stimulation in Channel 2 (980/UV). Finally, the combined use of chemical and cellular tools enables clinical nano-drugs to achieve a significant increase in tumor infiltration, thereby enhancing the efficacy of nano-chemotherapy.

Multifunctional Superparticles for Magnetically Targeted NIR-II Imaging and Photodynamic Therapy

Theranostics, the combination of diagnostics and therapies, has been considered as a promising strategy for clinical cancer treatment. Nonetheless, building a smart theranostic system with multifunction for different on-demand applications still remains elusive. Herein, an easy and user-friendly microemulsion based method is developed to modularly assemble upconversion nanoparticles (UCNPs) and Fe3 O4 nanoparticles together, forming multifunctional UCNPs/Fe3 O4 superparticles with highly integrated functionalities including the 808 nm excitation for real-time NIR-II imaging, magnetic targeting, and the upconversion luminescence upon 980 nm excitation for on-demand photodynamic therapy (PDT). With a magnet placed nearby the tumor, in vivo NIR-II imaging uncovers that superparticles tend to migrate toward the tumor and exhibit intense tumor accumulation, ≈6 folds higher than that without magnetic targeting 2 h after intravenous injection. NIR laser irradiation is then used to trigger PDT, obtaining an outstanding tumor elimination under magnetic tumor targeting, which shows a high potential to be applied in targeted cancer theranostics.

Advanced techniques for performing photodynamic therapy in deep-seated tissues

Photodynamic therapy (PDT) is a promising localized cancer treatment modality. It has been used successfully to treat a range of dermatological conditions with comparable efficacy to conventional treatments. However, some drawbacks limit the clinical utility of PDT in treating deep-seated tumors. Notably, the penetration limitation of UV and visible light, commonly applied to activate photosensitizers, makes PDT incompetent in treating deep-seated tumors. Development in light delivery technologies, especially fiber optics, led to improved clinical strategies for accessing deep tissues for irradiation. However, PDT efficacy issues remained partly due to light penetration limitations. In this review, we first summarized the current PDT applications for deep-seated tumor treatment. Then, the most recent progress in advanced techniques to overcome the light penetration limitation in PDT, including using functional nanomaterials that can either self-illuminate or be activated by near-infrared (NIR) light and X-rays as transducers, and implantable light delivery devices were discussed. Finally, current challenges and future opportunities of these technologies were discussed, which we hope may inspire the development of more effective techniques to enhance PDT efficacy against deep-seated tumors.

Bioimaging with Upconversion Nanoparticles

Bioimaging enables the spatiotemporal visualization of biological processes at various scales empowered by a range of different imaging modalities and contrast agents. Upconversion nanoparticles (UCNPs) represent a distinct type of such contrast agents with the potential to transform bioimaging due to their unique optical properties and functional design flexibilities. This review explores and discusses the opportunities, challenges, and limitations that UCNPs exhibit as bioimaging probes and highlights applications with spatial dimensions ranging from the single nanoparticle level to cellular, tissue, and whole animal imaging. We further summarized recent advancements in bioimaging applications enabled by UCNPs, including super-resolution techniques and multimodal imaging methods, and provide a perspective on the future potential of UCNP-based technologies in bioimaging research and clinical translation. This review may provide a valuable resource for researchers interested in exploring and applying UCNP-based bioimaging technologies.

Merging microfluidics with luminescence immunoassays for urgent point-of-care diagnostics of COVID-19

The Coronavirus disease 2019 (COVID-19) outbreak has urged the establishment of a global-wide rapid diagnostic system. Current widely-used tests for COVID-19 include nucleic acid assays, immunoassays, and radiological imaging. Immunoassays play an irreplaceable role in rapidly diagnosing COVID-19 and monitoring the patients for the assessment of their severity, risks of the immune storm, and prediction of treatment outcomes. Despite of the enormous needs for immunoassays, the widespread use of traditional immunoassay platforms is still limited by high cost and low automation, which are currently not suitable for point-of-care tests (POCTs). Microfluidic chips with the features of low consumption, high throughput, and integration, provide the potential to enable immunoassays for POCTs, especially in remote areas. Meanwhile, luminescence detection can be merged with immunoassays on microfluidic platforms for their good performance in quantification, sensitivity, and specificity. This review introduces both homogenous and heterogenous luminescence immunoassays with various microfluidic platforms. We also summarize the strengths and weaknesses of the categorized methods, highlighting their recent typical progress. Additionally, different microfluidic platforms are described for comparison. The latest advances in combining luminescence immunoassays with microfluidic platforms for POCTs of COVID-19 are further explained with antigens, antibodies, and related cytokines. Finally, challenges and future perspectives were discussed.

Synthesis of stable core-shell perovskite based nano-heterostructures

Despite having exceptional optical and photoelectric properties, the application of organometal halide perovskites (OHP) is restricted due to the limited penetration depth of the UV excitation light and poor stability. Attempts have been made to make composite materials by mixing other materials such as upconversion nanoparticles (UCNP) with OHP. In contrast to linear absorption and emission of OHP, the nonlinear upconversion of UCNP offers numerous advantages such as deep penetration depth of the near-infrared (NIR) excitation light, minimal photodamage to biological tissues, and negligible background interference, which offer great potential in various applications such as multiplexed optical encoding, three-dimensional displays, super-resolution bioimaging, and effective solar spectrum conversion. However, it is challenging to synthesize hybrid OHP-UCNP nanocrystals due to the inherent difference in crystal structures of hexagonal phase UCNP and cubic phase OHP. In this work, we report OHP-UCNP heterostructured nanocrystals synthesized via growing cubic phase NaGdF₄ UCNP over cubic phase CsPbBr₃ OHP in a seed-mediated process based on a very small lattice mismatch and then converting cubic phase UCNP to hexagonal phase through heating. The juxtaposition of UCNP over OHP in a single nanocrystal facilitates efficient energy transfer from UCNP to OHP under NIR excitation and acts as a protective layer improving the stability. The stability is further enhanced by coating an inert UCNP shell on the OHP-UCNP nano-heterostructures with the same UCNP material earlier used in the heterostructures. The coating demonstrated greater stability under continuous UV exposure and in harsh environments such as high temperatures and polar solvents. These NIR excitable perovskite-UCNP nano-heterostructures with improved stability have great potential for use in new optoelectronic and biological applications.

Nanocomposites based on lanthanide-doped upconversion nanoparticles: diverse designs and applications

Lanthanide-doped upconversion nanoparticles (UCNPs) have aroused extraordinary interest due to the unique physical and chemical properties. Combining UCNPs with other functional materials to construct nanocomposites and achieve synergistic effect abound recently, and the resulting nanocomposites have shown great potentials in various fields based on the specific design and components. This review presents a summary of diverse designs and synthesis strategies of UCNPs-based nanocomposites, including self-assembly, in-situ growth and epitaxial growth, as well as the emerging applications in bioimaging, cancer treatments, anti-counterfeiting, and photocatalytic fields. We then discuss the challenges, opportunities, and development tendency for developing UCNPs-based nanocomposites.

Switching the NIR upconversion of nanoparticles for the orthogonal activation of photoacoustic imaging and phototherapy

Phototheranostics based on upconversion nanoparticles (UCNPs) offer the integration of imaging diagnostics and phototherapeutics. However, the programmable control of the photoactivation of imaging and therapy with minimum side effects is challenging due to the lack of ideal switchable UCNPs agents. Here we demonstrate a facile strategy to switch the near infrared emission at 800 nm from rationally designed UCNPs by modulating the irradiation laser into pulse output. We further synthesize a theranostic nanoagent by combining with a photosensitizer and a photoabsorbing agent assembled on the UCNPs. The orthogonal activation of in vivo photoacoustic imaging and photodynamic therapy can be achieved by altering the excitation modes from pulse to continuous-wave output upon a single 980 nm laser. No obvious harmful effects during photoexcitation was identified, suggesting their use for long-term imaging-guidance and phototherapy. This work provides an approach to the orthogonal activation of imaging diagnostics and photodynamic therapeutics.

Immunotherapeutic nanoparticles: From autoimmune disease control to the development of vaccines

The development of nanoparticles (NPs) with potential therapeutic uses represents an area of vast interest in the scientific community during the last years. Recently, the pandemic caused by COVID-19 motivated a race for vaccines creation to overcome the crisis generated. This is a good demonstration that nanotechnology will most likely be the basis of future immunotherapy. Moreover, the number of publications based on nanosystems has significantly increased in recent years and it is expected that most of these developments can go on to experimentation in clinical stages soon. The therapeutic use of NPs to combat different diseases such as cancer, allergies or autoimmune diseases will depend on their characteristics, their targets, and the transported molecules. This review presents an in-depth analysis of recent advances that have been developed in order to obtain novel nanoparticulate based tools for the treatment of allergies, autoimmune diseases and for their use in vaccines. Moreover, it is highlighted that by providing targeted delivery an increase in the potential of vaccines to induce an immune response is expected in the future. Definitively, the here gathered analysis is a good demonstration that nanotechnology will be the basis of future immunotherapy.

Self-Assembly of Upconversion Nanoparticles Based Materials and Their Emerging Applications

In the past few decades, significant progress of the conventional upconversion nanoparticles (UCNPs) based nanoplatform has been achieved in many fields, and with the development of nanoscience and nanotechnology, more and more complex situations need a UCNPs based nanoplatform having multifunctions for specific multimodal or multiplexed applications. Through self-assembly, different UCNPs or UCNPs with other materials could be combined together within an entity. It is more like an ideal UCNPs nanoplatform, a unique system with the properties defined by its individual components as well as by the morphology of the composite. Various designs can show their different desired properties depending on the application situation. This review provides a complete summary on the optimization of the synthesis method for the recently designed UCNPs assemblies and summarizes various applications, including dual-modality cell imaging, molecular delivery, detection, and programmed control therapy. The challenges and limitations the UCNPs assembly faces and the potential solutions in this field are also presented.

Controlling upconversion in emerging multilayer core-shell nanostructures: from fundamentals to frontier applications

Lanthanide-based upconversion nanomaterials have recently attracted considerable attention in both fundamental research and various frontier applications owing to their excellent photon upconversion performance and favourable physicochemical properties. In particular, the emergence of multi-layer core-shell (MLCS) nanostructures offers a versatile and powerful tool to realize well-defined matrix compositions and spatial distributions of the dopant on the nanometer length scale. In contrast to the conventional nanomaterials and commonly investigated core-shell nanoparticles, the rational design of MLCS nanostructures allows us to deliberately introduce more functional properties into an upconversion system, thus providing unprecedented opportunities for the precise manipulation of energy transfer channels, the dynamic control of upconversion processes, the fine tuning of switchable emission colours and new functional integration at a single-particle level. In this review, we present a summary and discussion on the key aspects of the recent progress in lanthanide-based MLCS nanoparticles, including the manipulation of emission and lifetime, the switchable multicolour output and the lanthanide ionic interactions on the nanoscale. Benefitting from the multifunctional and versatile luminescence properties, the MLCS nanostructures exhibit great potential in diversities of frontier applications such as three-dimensional display, upconversion laser, optical memory, anti-counterfeiting, thermometry, bioimaging, and therapy. The outlook and challenges as well as perspectives for the research in MLCS nanostructure materials are also provided. This review would be greatly helpful in exploring new structural designs of lanthanide-based materials to further manipulate the upconversion phenomenon and expand their application boundaries.

Nanobiotechnology-assisted therapies to manage brain cancer in personalized manner

There are numerous investigated factors that limit brain cancer treatment efficacy such as ability of prescribed therapy to cross the blood-brain barrier (BBB), tumor specific delivery of a therapeutics, transport within brain interstitium, and resistance of tumor cells against therapies. Recent breakthroughs in the field of nano-biotechnology associated with developing multifunctional nano-theranostic emerged as an effective way to manage brain cancer in terms of higher efficacy and least possible adverse effects. Keeping challenges and state-of-art accomplishments into consideration, this review proposes a comprehensive, careful, and critical discussion focused on efficient nano-enabled platforms including nanocarriers for drug delivery across the BBB and nano-assisted therapies (e.g., nano-immunotherapy, nano-stem cell therapy, and nano-gene therapy) investigated for brain cancer treatment. Besides therapeutic efficacy point-of-view, efforts are being made to explore ways projected to tune such developed nano-therapeutic for treating patients in personalized manner via controlling size, drug loading, delivery, and retention. Personalized brain tumor management based on advanced nano-therapies can potentially lead to excellent therapeutic benefits based on unique genetic signatures in patients and their individual disease profile. Moreover, applicability of nano-systems as stimulants to manage the brain cancer growth factors has also been discussed in photodynamic therapy and radiotherapy. Overall, this review offers a comprehensive information on emerging opportunities in nanotechnology for advancing the brain cancer treatment.

Stokes and upconverted luminescence in Er3+/Yb3+-doped Y3Ga5O12 nano-garnets

The green, red, near-infrared and near-infrared-to-visible upconverted luminescence properties of Er3+/Yb3+ codoped Y3Ga5O12 nanocrystalline powders have been studied using laser spectroscopy. A diffuse reflectance and luminescence spectra confirm that Er3+ and Yb3+ ions occupy the Y3+ sites of the single-phase cubic nano-garnet. Very bright green and red luminescence of the Er3+ ions are detected by the naked eyes, even for a laser power as low as 15 mW, when the Yb3+ ions are excited at 970 nm. The red upconverted emission is more intense than that under direct excitation of the Er3+ ions. The power dependence and the dynamics of the near-infrared-to-green and near-infrared-to-red upconverted emissions show the existence of different two-photon energy transfer upconversion processes. The results here presented indicate that Er3+/Yb3+ codoped Y3Ga5O12 can be a good candidate as an optical nanoheater and nanothermometer in biomedicine applications in the first biological window.

Targeting drug delivery with light: A highly focused approach

Light is a uniquely powerful tool for controlling molecular events in biology. No other external input (e.g., heat, ultrasound, magnetic field) can be so tightly focused or so highly regulated as a clinical laser. Drug delivery vehicles that can be photonically activated have been developed across many platforms, from the simplest "caging" of therapeutics in a prodrug form, to more complex micelles and circulating liposomes that improve drug uptake and efficacy, to large-scale hydrogel platforms that can be used to protect and deliver macromolecular agents including full-length proteins. In this Review, we discuss recent innovations in photosensitive drug delivery and highlight future opportunities to engineer and exploit such light-responsive technologies in the clinical setting.

Exploring Heterostructured Upconversion Nanoparticles: From Rational Engineering to Diverse Applications

Upconversion nanoparticles (UCNPs) represent a class of optical nanomaterials that can convert low-energy excitation photons to high-energy fluorescence emissions. On the basis of UCNPs, heterostructured UCNPs, consisting of UCNPs and other functional counterparts (metals, semiconductors, polymers, etc.), present an intriguing system in which the physicochemical properties are largely influenced by the entire assembled particle and also by the morphology, dimension, and composition of each individual component. As multicomponent nanomaterials, heterostructured UCNPs can overcome challenges associated with a single component and exhibit bifunctional or multifunctional properties, which can further expand their applications in bioimaging, biodetection, and phototherapy. In this review, we provide a summary of recent achievements in the field of heterostructured UCNPs in the aspects of construction strategies, synthetic approaches, and types of heterostructured UCNPs. This review also summarizes the trends in biomedical applications of heterostructured UCNPs and discusses the challenges and potential solutions in this field.

Orthogonal Emissive Upconversion Nanoparticles: Material Design and Applications

Upconversion nanoparticles (UCNPs) have gone beyond traditional fluorophores in a lot of fields due to the outstanding features such as sharp excitation and emission bands, chemical and photo stability of high quality, low auto fluorescence, and high tissue permeation depth of the near-infrared irradiation light used for excitation. Conventional UCNPs carrying single/multiple emissions under a single excitation wavelength can be only employed in concurrent activation, orthogonal emissive upconversion nanoparticles (OUCNPs) with the emissions, a kind of luminescence reliant on excitation, in which by switching the external excitation different lanthanide activators can adopt independent way to control the emission, is more like an ideal UCNPs nanoplatform which can switch their activated emissions depending upon the different application for which it is used at the right time when necessary. This review summaries what has been achieved on the synthesis optimization of designed OUCNPs in recent years and sums up various applications including bioimaging, photo-switching, and programmable control process. And also, the limitations OUCNPs face, and the efforts that have been made to overcome these limitations are discussed.

Controllable Assembly of Upconversion Nanoparticles Enhanced Tumor Cell Penetration and Killing Efficiency

The use of upconversion nanoparticles (UCNPs) for treating deep-seated cancers and large tumors has recently been gaining momentum. Conventional approaches for loading photosensitizers (PS) to UCNPs using noncovalent physical adsorption and covalent conjugation had been previously described. However, these methods are time-consuming and require extra modification steps. Incorporating PS loading during the controlled UCNPs assembly process is seldom reported. In this study, an amphiphilic copolymer, poly(styrene-co-maleic anhydride), is used to instruct UCNPs assembly formations into well-controlled UCNPs clusters of various sizes, and the gap zones formed between individual UCNPs can be used to encapsulate PS. This nanostructure production process results in a considerably simpler and reliable method to load PS and other compounds. Also, after considering factors such as PS loading quantity, penetration in 3D bladder tumor organoids, and singlet oxygen production, the small UCNPs clusters displayed superior cell killing efficacy compared to single and big sized clusters. Therefore, these UCNPs clusters with different sizes could facilitate a clear and deep understanding of nanoparticle-based delivery platform systems for cell killing and may pave a new way for other fields of UCNPs based applications.

Nanosized Anti-Stokes Phosphors for Antitumor Drug Delivery and Solid Tumor Theranostics

Abstract-Theranostics is the direction in modern biomedicine aimed at developing drugs that combine the capabilities of diagnosis and therapy of tumors in one agent. Upconversion nanophosphors (UCNPs) are inorganic crystalline materials that can be used to create a nanoplatform providing diagnostic and therapeutic modalities. They have been proposed as luminescent markers for optical imaging of biological tissue due to their anti-Stokes luminescence, lack of photodegradation and low toxicity. In this article, UCNPs as a theranostic agent for both optical imaging and delivery of anticancer drugs have been offered. To obtain biocompatible nanocomplexes, UCNP surface with a core/shell structure of NaYF₄:Yb³⁺Tm³⁺/NaYF₄ was modified with polylactic acid in the presence of various stabilizers (dextran, polyvinyl alcohol, and poly-N-vinylpyrrolidone). To give the therapeutic modality to the nanocomplex, the antitumor antibiotic doxorubicin was loaded into the polymer shell. The loading efficiency was up to 0.1 mg per 1 mg UCNPs. The toxicity and the intracellular accumulation of nanocomplexes were evaluated in vitro. It was concluded that the modification of UCNPs with polylactic acid provides the transport of doxorubicin, allowing the combination of diagnostic and therapeutic modalities in one agent.