Dispersion stability and biocompatibility of four ligand-exchanged NaYF4: Yb, Er upconversion nanoparticles

Effect of Surface Modification on the Luminescence of Individual Upconversion Nanoparticles

Lanthanide-doped upconversion nanoparticles (UCNPs) hold promise for single-molecule imaging owing to their excellent photostability and minimal autofluorescence. However, their limited water dispersibility, often from the hydrophobic oleic acid ligand during synthesis, is a challenge. To address this, various surface modification strategies' impact on single-particle upconversion luminescence are studied. UCNPs are made hydrophilic through methods like ligand exchange with dye IR806, HCl or NOBF4 treatment, silica coating (SiO2 or mesoporous mSiO2), and self-assembly with polymer of DSPE-PEG or F127. The studies revealed that UCNPs modified with NOBF4 and DSPE-PEG exhibited notably higher single-particle brightness with minimal quenching (3% and 8%, respectively), followed by SiO2, F127, IR806, mSiO2, and HCl (84% quenching). HCl disrupted UCNPs's crystal lattice, weakening luminescence, while mSiO2 absorbed solvent molecules, causing luminescence quenching. Energy transfer to IR806 also reduced the brightness. Additionally, a prevalence of upconversion red emission over green is observed, with the red-to-green ratio increasing with irradiance. UCNPs coated with DSPE-PEG exhibited the brightest single-particle luminescence in water, retaining 48% of its original emission due to a lower critical micelle concentration and superior water protection. In summary, the investigation provides valuable insights into the role of surface chemistry on UCNPs at the single-particle level.

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.

Energy transfer between optically trapped single ligand-free upconversion nanoparticle and dye

The quenching in luminescence emission of an optically trapped ligand-free hydrophilic NaYF₄:Yb, Er upconversion nanoparticle (UCNP) as a function of rose Bengal dye molecule is investigated here. The removal of oleate capping of the as-prepared UCNPs was achieved via acid treatment and characterized via FTIR and Raman spectroscopic techniques. Further, the capping removed hydrophilic single UCNP is optically trapped and the emission studies were carried out as a function of excitation laser power. Compared to the studies using the bulk solution, the single UCNP luminescence spectrum exhibited additional spectral lines. The excitation laser power-dependent studies using the bulk solution yield a slope value between 1 and 2 for Blue, Green 1, Green 2, and Red emission and thus indicate that upconversion is a two-photon upconversion process. On the other hand, in the case of laser power-dependent studies on an optically trapped single-particle study, Blue and Green 1 yield a slope value of less than 1 whereas Green 2 and Red emission gave a slope value between 1 and 2. The energy transfer studies between an optically trapped ligand-free single UCNP and the rose Bengal dye show a concentration-dependent quenching in the emission of Green emissions and illustrate the potential of developing sensor platforms.

A Comprehensive Review on Upconversion Nanomaterials-Based Fluorescent Sensor for Environment, Biology, Food and Medicine Applications

Near-infrared-excited upconversion nanoparticles (UCNPs) have multicolor emissions, a low auto-fluorescence background, a high chemical stability, and a long fluorescence lifetime. The fluorescent probes based on UCNPs have achieved great success in the analysis of different samples. Here, we presented the research results of UCNPs probes utilized in analytical applications including environment, biology, food and medicine in the last five years; we also introduced the design and construction of upconversion optical sensing platforms. Future trends and challenges of the UCNPs used in the analytical field have also been discussed with particular emphasis.

Upconversion Nanomaterials in Bioimaging and Biosensor Applications and Their Biological Response

In recent decades, upconversion nanomaterials (UCNMs) have attracted considerable research interest because of their unique optical properties, such as large anti-Stokes shifts, sharp emissions, non-photobleaching, and long lifetime. These unique properties make them ideal candidates for unified applications in biomedical fields, including drug delivery, bioimaging, biosensing, and photodynamic therapy for specific cancers. This review describes the general mechanisms of upconversion, synthesis methods, and potential applications in biology and their biological responses. Additionally, the biological toxicity of UCNMs is explained and summarized with the associated intracellular association mechanisms. Finally, the prospects and future challenges of UCNMs at the clinical level in biological applications are described, along with a summary of opportunity for biological as well as clinical applications of UCNMs.

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.

Aspect Ratio of PEGylated Upconversion Nanocrystals Affects the Cellular Uptake In Vitro and In Vivo

The central nervous system (CNS) is protected by the blood-brain barrier (BBB), which acts as a physical barrier to regulate and prevent the uptake of endogenous metabolites and xenobiotics. However, the BBB prevents most non-lipophilic drugs from reaching the CNS following systematic administration. Therefore, there is considerable interest in identifying drug carriers that can maintain the biostability of therapeutic molecules and target their transport across the BBB. In this regard, upconversion nanoparticles (UCNPs) have become popular as a nanoparticle-based solution to this problem, with the additional benefit that they display unique properties for in vivo visualization. The majority of studies to date have explored basic spherical UCNPs for drug delivery applications. However, the biophysical properties of UCNPs, cell uptake and BBB transport have not been thoroughly investigated. In this study, we described a one-pot seed-mediated approach to precisely control longitudinal growth to produce bright UCNPs with various aspect ratios. We have systematically evaluated the effects of the physical aspect ratios and PEGylation of UCNPs on cellular uptake in different cell lines and an in vivo zebrafish model. We found that PEGylated the original UCNPs can enhance their biostability and cell uptake capacity. We identify an optimal aspect ratio for UCNP uptake into several different types of cultured cells, finding that this is generally in the ratio of 2 (length/width). This data provides a crucial clue for further optimizing UCNPs as a drug carrier to deliver therapeutic agents into the CNS. STATEMENT OF SIGNIFICANCE: The central nervous system (CNS) is protected by the blood-brain barrier (BBB), which acts as a highly selective semipermeable barrier of endothelial cells to regulate and prevent the uptake of toxins and pathogens. However, the BBB prevents most non-lipophilic drugs from reaching the CNS following systematic administration. The proposed research is significant because identifying the aspect ratio of drug carriers that maintains the biostability of therapeutic molecules and targets their transport across the blood-brain barrier (BBB) is crucial for designing an efficient drug delivery system. Therefore, this research provides a vital clue for further optimizing UCNPs as drug carriers to deliver therapeutic molecules into the brain.

One step preparation of multifunctional poly (ether sulfone) thin films with potential for wound dressing

The increasing demand for higher-quality medical care has resulted in the obsolescence of traditional biomaterials. Medical care is currently transitioning from an era depending on single-functional biomaterials to one that is supported by multifunctional and stable biomaterials. Herein, long-lasting multifunctional poly(ether sulfone) thin films (MPFs) containing heparin-mimic groups and a quaternary ammonium compound (QAC) were prepared via semi-interpenetrating polymer network (SIPN) strategy. The MPFs, with rough surface and inner finger-like macrovoid, had better hydrophilicity and anti-protein fouling ability, as revealed by scanning electron microscopy (SEM), atomic force microscope (AFM) and water contact angle (WCA) and protein adsorption tests. The results of platelet adhesion and activation, and clotting time confirmed that the hemocompatibility of the MPFs was significantly improved. From cell culture and germ-culture test, it was noted that the overall trend of human umbilical vein endothelial cell (HUVEC) proliferation was enhanced by a combination of heparin-mimic groups and QAC, whereas the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was significantly prohibited. In addition, the MPFs were capable of modulating the expression level of basic fibroblast growth factor (bFGF) and transforming growth factor-beta1 (TGF-β1) in fibroblast, which was beneficial to controlling the formation of hypertrophic scar. In summary, the MPFs had potential to be used in the field of wound management and the study might help guide the design of surface structure of wound dressing.

Antitumor Effect of Co-Loading Natural Active Compound of Okofuran (Usenamine) and Photosensitizer Nano-Liposomes

Objective: In this study, we developed a nano-liposome (LIP-RUA) to evaluate the in vitro anti-lung cancer activity. In this regard, nano-liposome co-loaded with photosensitizer (RB), upconverting nanoparticles (UCNPs), and natural active compound usenamine (ACU). Methods: LIP-RUA was obtained by encapsulating ACU/RB/UCNPs by thin film dispersion method. The physicochemical properties were investigated by using an instrument; the efficiency of liposomes producing reactive oxygen species (ROS) was detected by SOSG probe; the uptake of LIP-RUA by A549 lung cancer cells was observed by confocal microscopy. Results: The particle size of the prepared LIP-RUA was about 150 nm, the surface potential was about −12 mV, and the entrapment efficiency of RB and ACU reached 54.5% and 86.5%, respectively. Experimental tasks showed that LIP-RUA could significantly improve the growth inhibitory effect of the drug on lung cancer cells, and the median effective inhibitory concentration (IC50) under laser irradiation was 15.33 μmol/L. Conclusion: LIP-RUA provides a new idea for the combination of photodynamic chemotherapy for the treatment of lung cancer. The liposome platform is expected to enhance the in vivo penetration of photodynamic therapy and the combined effect of photodynamic chemotherapy.

Recent Advances in Near Infrared Upconverting Nanomaterials for Targeted Photodynamic Therapy of Cancer

Photodynamic therapy (PDT) is a well-established treatment of cancer that uses the toxic reactive oxygen species, including singlet oxygen (1O2), generated by photosensitiser drugs following irradiation of a specific wavelength to destroy the cancerous cells and tumours. Visible light is commonly used as the excitation source in PDT, which is not ideal for cancer treatment due to its reduced tissue penetration, and thus inefficiency to treat deep-lying tumours. Additionally, these wavelengths exhibit elevated autofluorescence background from the biological tissues which hinders optical biomedical imaging. An alternative to UV-Vis irradiation is the use of near infrared (NIR) excitation for PDT. This can be achieved using upconverting nanoparticles (UCNPs) functionalised with photosensitiser (PS) drugs where UCNPs can be used as an indirect excitation source for the activation of PS drugs yielding to the production of singlet 1O2 following NIR excitation. The use of nanoparticles for PDT is also beneficial due to their tumour targeting capability, either passively via the enhanced permeability and retention (EPR) effect or actively via stimuli-responsive targeting and ligand-mediated targeting (ie. using recognition units that can bind specific receptors only present or overexpressed on tumour cells). Here, we review recent advances in NIR upconverting nanomaterials for PDT of cancer with a clear distinction between those reported nanoparticles that could potentially target the tumour due to accumulation via the EPR effect (passive targeting) and nanoparticle-based systems that contain targeting agents with the aim of actively target the tumour via a molecular recognition process.

Influence of the synthesis route on the spectroscopic, cytotoxic, and temperature-sensing properties of oleate-capped and ligand-free core/shell nanoparticles

The right choice of synthesis route for upconverting nanoparticles (UCNPs) is crucial for obtaining a well-defined product with a specific application capability. Thus we decided to compare the physicochemical, cytotoxic, and temperature-sensing properties of UCNPs obtained from different rare earth (RE) ions, which has been made for the first time in a single study. The core/shell NaYF₄:Yb³⁺,Er³⁺/NaYF₄ UCNPs were obtained by reaction in a mixture of oleic acid and octadecene, and their highly stable water colloids were prepared using the ligand-free modification method. Both oleate-capped and ligand-free UCNPs exhibited a bright upconversion emission upon 975 nm excitation. Moreover, slope values, emission quantum yields, and luminescence lifetimes confirmed an effective energy transfer between the Yb³⁺ and Er³⁺ ions. Additionally, the water colloids of the UCNPs showed temperature-sensing properties with a good thermal sensitivity level, higher than 1 % K^-1 at 358 K. Evaluation of the cytotoxicity profiles of the obtained products indicated that cell viability was decreased in a dose-dependent manner in the analyzed concentration range.

Enhancing the Upconversion Luminescence and Sensitivity of Nanothermometry through Advanced Design of Dumbbell-Shaped Structured Nanoparticles

The core-shell engineering of lanthanide-doped nanoparticles has captured considerable attention because it can safeguard the luminescence intensity of the core by reducing surface defects. However, the limited surface area of the traditional spherical core-shell structure hinders the further breakthrough of the brightness. Herein, a unique NaYF₄:Yb³⁺/RE³⁺@NaYF₄:Yb³⁺/RE³⁺@NaNdF₄:Yb³⁺ (RE³⁺ = Ho³⁺ or Er³⁺) dumbbell-shaped multilayer nanoparticle featuring a high surface area is reported. Its upconversion luminescence intensity is higher than that of the conventional spherical core-shell structure. A thorough investigation is performed on the luminescence and thermometric mechanisms of Ho³⁺/Er³⁺ distributed in the core and the first shell. Remarkably, when Ho³⁺/Er³⁺ ions are distributed in the first shell, the relative sensitivity of the biological luminescence nanothermometer composed of downshifting near-infrared emissions is increased to 2.543% K^-1 (328 K), which considerably exceeds most reported values. The increased value is attributed to the more thermal-sensitive phonon-assisted energy transfer. For potential biological applications, dumbbell-shaped nanoparticles (DSNPs) with hydrophilic modification show excellent thermometric performance and high tissue penetration depth. Overall, the insights provided by this work will broaden the scope of novel DSNPs in the fields of luminescence and nanothermometry.

Upconversion Nanoparticles Encapsulated with Molecularly Imprinted Amphiphilic Copolymer as a Fluorescent Probe for Specific Biorecognition

A fluorescent probe for specific biorecognition was prepared by a facile method in which amphiphilic random copolymers were encapsulated with hydrophobic upconversion nanoparticles (UCNPs). This method quickly converted the hydrophobic UCNPs to hydrophilic UNCPs. Moreover, the self-folding ability of the amphiphilic copolymers allowed the formation of molecular imprinting polymers with template-shaped cavities. LiYF4:Yb3+/Tm3+@LiYF4:Yb3+ UCNP with up-conversion emission in the visible light region was prepared; this step was followed by the synthesis of an amphiphilic random copolymer, poly(methacrylate acid-co-octadecene) (poly(MAA-co-OD)). Combining the UCNPs and poly(MAA-co-OD) with the templates afforded a micelle-like structure. After removing the templates, UCNPs encapsulated with the molecularly imprinted polymer (MIP) (UCNPs@MIP) were obtained. The adsorption capacities of UCNPs@MIP bound with albumin and hemoglobin, respectively, were compared. The results showed that albumin was more easily bound to UCNPs@MIP than to hemoglobin because of the effect of protein conformation. The feasibility of using UCNPs@MIP as a fluorescent probe was also studied. The results showed that the fluorescence was quenched when hemoglobin was adsorbed on UCNPs@MIP; however, this was not observed for albumin. This fluorescence quenching is attributed to Förster resonance energy transfer (FRET) and overlap of the absorption spectrum of hemoglobin with the fluorescence spectrum of UCNPs@MIP. To our knowledge, the encapsulation approach for fabricating the UCNPs@MIP nanocomposite, which was further used as a fluorescent probe, might be the first report on specific biorecognition.

Upconversion nanoparticle-assisted single-molecule assay for detecting circulating antigens of aggressive prostate cancer

Sensitive and quantitative detection of molecular biomarkers is crucial for the early diagnosis of diseases like metabolic syndrome and cancer. Here we present a single-molecule sandwich immunoassay by imaging the number of single nanoparticles to diagnose aggressive prostate cancer. Our assay employed the photo-stable upconversion nanoparticles (UCNPs) as labels to detect the four types of circulating antigens in blood circulation, including glypican-1 (GPC-1), leptin, osteopontin (OPN), and vascular endothelial growth factor (VEGF), as their serum concentrations indicate aggressive prostate cancer. Under a wide-field microscope, a single UCNP doped with thousands of lanthanide ions can emit sufficiently bright anti-Stokes' luminescence to become quantitatively detectable. By counting every single streptavidin-functionalized UCNP which specifically labeled on each sandwich immune complex across multiple fields of views, we achieved the Limit of Detection (LOD) of 0.0123 ng/ml, 0.2711 ng/ml, 0.1238 ng/ml, and 0.0158 ng/ml for GPC-1, leptin, OPN and VEGF, respectively. The serum circulating level of GPC-1, leptin, OPN, and VEGF in a mixture of 10 healthy normal human serum was 25.17 ng/ml, 18.04 ng/ml, 11.34 ng/ml, and 1.55 ng/ml, which was within the assay dynamic detection range for each analyte. Moreover, a 20% increase of GPC-1 and OPN was observed by spiking the normal human serum with recombinant antigens to confirm the accuracy of the assay. We observed no cross-reactivity among the four biomarker analytes, which eliminates the false positives and enhances the detection accuracy. The developed single upconversion nanoparticle-assisted single-molecule assay suggests its potential in clinical usage for prostate cancer detection by monitoring tiny concentration differences in a panel of serum biomarkers.

Polymer-Functionalized Upconversion Nanoparticles for Light/Imaging-Guided Drug Delivery

The strong upconversion luminescence (UCL) of upconversion nanoparticles (UCNPs) endows the nanoparticles with attractive features for combined imaging and drug delivery. UCNPs convert near-infrared (NIR) light into light of shorter wavelengths such as light in the ultraviolet (UV) and visible regions, which can be used for light-guided drug delivery. Although light-responsive drug delivery systems as such have been known for many years, their application in medicine is limited, as strong UV-light can be damaging to tissue; moreover, UV light will not penetrate deeply into the skin, an issue that UCNPs can now address. However, UCNPs, as obtained after synthesis, are usually hydrophobic and require further surface functionalization to be stable in plasma. Polymers can serve as versatile surface coatings, as they can provide good colloidal stability, prevent the formation of a protein corona, provide a matrix for drugs, and be stimuli-responsive. In this Review, we provide a brief overview of the most recent progress in the synthesis of UCNPs with different shapes/sizes. We will then discuss the purpose of polymer coating for drug delivery before summarizing the strategies to coat UCNPs with various polymers. We will introduce the different polymers that have so far been used to coat UCNPs with the purpose to create a drug delivery system, focusing in detail on light-responsive polymers. To expand the application of UCNPs to allow photothermal therapy or magnetic resonance imaging (MRI) or to simply enhance the loading capacity of drugs, UCNPs were often combined with other materials to generate multifunctional nanoparticles such as carbon-based NPs and nanoMOFs. We then conclude with a discussion on drug loading and release and summarize the current knowledge on the toxicity of these polymer-coated UCNPs.

Lanthanide ion (Ln3+ )-based upconversion sensor for quantification of food contaminants: A review

The food safety issue has gradually become the focus of attention in modern society. The presence of food contaminants poses a threat to human health and there are a number of interesting researches on the detection of food contaminants. Upconversion nanoparticles (UCNPs) are superior to other fluorescence materials, considering the benefits of large anti-Stokes shifts, high chemical stability, non-autofluorescence, good light penetration ability, and low toxicity. These properties render UCNPs promising candidates as luminescent labels in biodetection, which provides opportunities as a sensitive, accurate, and rapid detection method. This paper intended to review the research progress of food contaminants detection by UCNPs-based sensors. We have proposed the key criteria for UCNPs in the detection of food contaminants. Additionally, it highlighted the construction process of the UCNPs-based sensors, which includes the synthesis and modification of UCNPs, selection of the recognition elements, and consideration of the detection principle. Moreover, six kinds of food contaminants detected by UCNPs technology in the past 5 years have been summarized and discussed fairly. Last but not least, it is outlined that UCNPs have great potential to be applied in food safety detection and threw new insight into the challenges ahead.

The Use of Upconversion Nanoparticles in Prostate Cancer Photodynamic Therapy

Photodynamic Therapy (PDT) is a cancer treatment that uses light, a photosensitizer, and oxygen to destroy tumors. This article is a review of approaches to the treatment of prostate cancer applying upconversion nanoparticles (UCNPs). UCNPs have become a phenomenon that are rapidly gaining recognition in medicine. They have proven to be highly selective and specific and present a powerful tool in the diagnosis and treatment of prostate cancer. Prostate cancer is a huge health problem in Western countries. Its early detection can significantly improve patients’ prognosis, but currently used diagnostic methods leave much to be desired. Recently developed methodologies regarding UCNP research between the years 2021 and 2014 for prostate cancer PDT will also be discussed. Current limitations in PDT include tissue irradiation with visible wavelengths that have a short tissue penetration depth. PDT with the objectives to synthesize UCNPs composed of a lanthanide core with a coating of adsorbed dye that will generate fluorescence after excitation with near-infrared light to illuminate deep tissue is a subject of intense research in prostate cancer.

Multicomponent thermosensitive lipid complexes enhance desmoplastic tumor therapy through boosting anti-angiogenesis and synergistic strategy

Currently, the chemotherapy drugs-loaded thermosensitive liposomes have not shown an over standard of clinical effects compared to preclinical trials. In addition to the limiting factors of clinical trial design and heating device, abnormal angiogenesis in desmoplastic tumor is a key factor for unexpected clinical efficacy. Malformed tumor vasculature may result in reduced vascular transport and the heterogeneous distribution of thermosensitive liposomes in tumor. Here, we report an anti-angiogenesis strategy through hypoxia-inducible factors (HIF)-1α-vascular endothelial growth factor (VEGF) axis based on icaritin and coix seed oil dual loaded multicomponent thermosensitive lipid complexes (IC-ML). IC-ML could downregulate the HIF-1α expression in HepG2 cells with a synergetic antitumor effect. In addition, HepG2 + LX-2 cells co-cultured 3D tumor spheres administered IC-ML showed the strongest penetration and inhibition of growth. Accordingly, IC-ML displayed improved tumor penetration and superior synergistic antitumor efficacy with HIF-1α-VEGF downregulation in vivo under mild hyperthermia. The improvement of antitumor efficacy of IC-ML comes from the anti-angiogenesis strategy and comprehensive tumor microenvironment remodeling, including depletion of cancer-associated fibroblasts as well as inhibition of M2-type tumor associated macrophage infiltration in desmoplastic tumor. This study proposes a novel multicomponent synergistic antitumor strategy to improve the therapeutic potential of thermosensitive lipid complexes for hepatocellular carcinoma.

Improvement of luminescence properties of NaYF4 :Yb3+ /Er3+ upconversion materials by a cross-relaxation mechanism based on co-doped Ho3+ ion concentrations

NaYF₄ :Yb³⁺ /Er³⁺ /Ho³⁺ nanophosphors were successfully synthesized using a solvothermal method and with various concentrations of Ho³⁺ ions. The crystal structure, grain size, morphology, and luminescence properties were analyzed by X-ray diffraction, field-emission scanning electron microscopy, and photoluminescence measurements. All samples were crystallized as a cubic structure; it was confirmed that all samples exhibited strong green emission and weak red emission generated at a particular level of the activated ions. The strongest upconversion fluorescence intensity was observed in the Ho³⁺ and Er³⁺ ions co-doped NaYF₄ materials with a Ho³⁺ ion concentration of 0.005 mol. Only the green fluorescence intensity at the 542 nm centre increased strongly due to the ⁴ S_3/2 →⁴ I_15/2 energy transfer. This increase in upconversion fluorescence intensity at a selected wavelength was described as a cross-relaxation mechanism due to the addition of Ho³⁺ ions.

Effect of different silica coatings on the toxicity of upconversion nanoparticles on RAW 264.7 macrophage cells

Upconversion nanoparticles (UCNPs), consisting of NaYF₄ doped with 18% Yb and 2% Er, were coated with microporous silica shells with thickness values of 7 ± 2 and 21 ± 3 nm. Subsequently, the negatively charged particles were functionalized with N-(6-aminohexyl)-3-aminopropyltrimethoxysilane (AHAPS), which provide a positive charge to the nanoparticle surface. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements revealed that, over the course of 24h, particles with thicker shells release fewer lanthanide ions than particles with thinner shells. However, even a 21 ± 3 nm thick silica layer does not entirely block the disintegration process of the UCNPs. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and cell cytometry measurements performed on macrophages (RAW 264.7 cells) indicate that cells treated with amino-functionalized particles with a thicker silica shell have a higher viability than those incubated with UCNPs with a thinner silica shell, even if more particles with a thicker shell are taken up. This effect is less significant for negatively charged particles. Cell cycle analyses with amino-functionalized particles also confirm that thicker silica shells reduce cytotoxicity. Thus, growing silica shells to a sufficient thickness is a simple approach to minimize the cytotoxicity of UCNPs.

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.

Bright Blue, Green, and Red Luminescence from Dye-Sensitized Core@Shell Upconversion Nanophosphors under 800 nm Near-Infrared Light

In this study, Li-based blue- and green-emitting core@shell (C@S) upconversion nanophosphors (UCNPs) and NaGdF4-based red-emitting C@S UCNPs were synthesized, and IR-808 dyes were conjugated with the C@S UCNPs to enhance upconversion (UC) luminescence. The surface of the as-synthesized C@S UCNPs, which was originally capped with oleic acid, was modified with BF4- to conjugate the IR-808 dye having a carboxyl functional group to the surface of the UCNPs. After the conjugation with IR-808 dyes, absorbance of the UCNPs was significantly increased. As a result, dye-sensitized blue (B)-, green (G)-, and red (R)-emitting UCNPs exhibited 87-fold, 10.8-fold, and 110-fold enhanced UC luminescence compared with B-, G-, and R-emitting Nd3+-doped C@S UCNPs under 800 nm near-infrared (NIR) light excitation, respectively. Consequently, dye-sensitized UCNPs exhibiting strong UC luminescence under 800 nm NIR light excitation have high applicability in a variety of biological applications.

Halide perovskite nanocrystals for multiphoton applications

Halide perovskite nanocrystals (NCs) are a unique class of NCs with novel properties distinct from those of traditional semiconductor NCs. These exceptional properties of defect tolerance, large absorption coefficients, high brightness, and narrow emission linewidths stem from their atypical band structure. Their facile synthesis and broad colour tunability have attracted widespread interest for application in light emitting devices and lasers. One fledging niche area is the field of multiphoton excited emission where their giant nonlinear optical action cross-sections are highly favorable for imaging applications. This Frontier article examines the state-of-the-art in perovskite NCs for multiphoton applications from the materials science and physics perspectives that include their synthesis and nonlinear optical characterization. Opportunities and challenges of these exceptional NCs as potential fluorescent labels for multiphoton deep tissue microscopy are also highlighted.