A facile hydrothermal synthesis of highly luminescent NaYF4:Yb3+/Er3+ upconversion nanoparticles and their biomonitoring capability

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.

Phototherapy in cancer treatment: strategies and challenges

Phototherapy has emerged as a promising modality in cancer treatment, garnering considerable attention for its minimal side effects, exceptional spatial selectivity, and optimal preservation of normal tissue function. This innovative approach primarily encompasses three distinct paradigms: Photodynamic Therapy (PDT), Photothermal Therapy (PTT), and Photoimmunotherapy (PIT). Each of these modalities exerts its antitumor effects through unique mechanisms-specifically, the generation of reactive oxygen species (ROS), heat, and immune responses, respectively. However, significant challenges impede the advancement and clinical application of phototherapy. These include inadequate ROS production rates, subpar photothermal conversion efficiency, difficulties in tumor targeting, and unfavorable physicochemical properties inherent to traditional phototherapeutic agents (PTs). Additionally, the hypoxic microenvironment typical of tumors complicates therapeutic efficacy due to limited agent penetration in deep-seated lesions. To address these limitations, ongoing research is fervently exploring innovative solutions. The unique advantages offered by nano-PTs and nanocarrier systems aim to enhance traditional approaches' effectiveness. Strategies such as generating oxygen in situ within tumors or inhibiting mitochondrial respiration while targeting the HIF-1α pathway may alleviate tumor hypoxia. Moreover, utilizing self-luminescent materials, near-infrared excitation sources, non-photoactivated sensitizers, and wireless light delivery systems can improve light penetration. Furthermore, integrating immunoadjuvants and modulating immunosuppressive cell populations while deploying immune checkpoint inhibitors holds promise for enhancing immunogenic cell death through PIT. This review seeks to elucidate the fundamental principles and biological implications of phototherapy while discussing dominant mechanisms and advanced strategies designed to overcome existing challenges-ultimately illuminating pathways for future research aimed at amplifying this intervention's therapeutic efficacy.

WITHDRAWN: Biomarker Detection and Therapy of Parkinson's and Alzheimer's disease using upconversion based approach: A Comprehensive Review

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Advancements in tantalum based nanoparticles for integrated imaging and photothermal therapy in cancer management

Tantalum-based nanoparticles (TaNPs) have emerged as promising tools in cancer management, owing to their unique properties that facilitate innovative imaging and photothermal therapy applications. This review provides a comprehensive overview of recent advancements in TaNPs, emphasizing their potential in oncology. Key features include excellent biocompatibility, efficient photothermal conversion, and the ability to integrate multifunctional capabilities, such as targeted drug delivery and enhanced imaging. Despite these advantages, challenges remain in establishing long-term biocompatibility, optimizing therapeutic efficacy through surface modifications, and advancing imaging techniques for real-time monitoring. Strategic approaches to address these challenges include surface modifications like PEGylation to improve biocompatibility, precise control over size and shape for effective photothermal therapy, and the development of biodegradable TaNPs for safe elimination from the body. Furthermore, integrating advanced imaging modalities-such as photoacoustic imaging, magnetic resonance imaging (MRI), and computed tomography (CT)-enable real-time tracking of TaNPs in vivo, which is crucial for clinical applications. Personalized medicine strategies that leverage biomarkers and genetic profiling also hold promise for tailoring TaNP-based therapies to individual patient profiles, thereby enhancing treatment efficacy and minimizing side effects. In conclusion, TaNPs represent a significant advancement in nanomedicine, poised to transform cancer treatment paradigms while expanding into various biomedical applications.

Integration of 3D Fluorescence Imaging and Luminescent Thermometry with Core-Shell Engineered NaYF4:Nd3+/Yb3+/Ho3+ Nanoparticles

The design of rare-earth-doped upconversion/downshifting nanoparticles (NPs) for theoretical use in nanomedicine has garnered considerable interest. Previous research has emphasized luminescent nanothermometry and photothermal therapy, while three-dimensional (3D) near-infrared (NIR) luminescent tracers have received less attention. Our study introduces Nd3+-, Yb3+-, and Ho3+-doped NaYF4 core-shell luminescent NPs as potential multiparametric nanothermometers and NIR imaging tracers. Nd3+ sensitizes at 804 nm, while Yb3+ bridges to activators Ho3+. We evaluated the photoluminescence properties of Nd3+-, Yb3+-, and Ho3+-doped core and core-shell NPs synthesized via polyol-mediated and thermal decomposition methods. The NaYF4:NdYbHo(7/15/3%)@NaYF4:Nd(15%) core-shell NPs demonstrate competitive nanothermometry capabilities. Specifically, the polyol-synthesized sample exhibits a sensitivity of 0.27% K-1 at 313 K (40 °C), whereas the thermally decomposed synthesized sample shows a significantly higher sensitivity of 0.55% K-1 at 313 K (40 °C) in the near-infrared range. Control samples indicate back energy transfer processes from both Yb and Ho to Nd, while Yb to Ho energy transfer enhances Ho3+-driven upconversion transitions in green and red wavelengths, suggesting promise for photodynamic therapy. Fluorescence molecular tomography confirms 3D NIR fluorescence nanoparticle localization in a biological media after injection, highlighting the potential of core-shell NPs as NIR luminescent tracers. The strategy's clinical impact lies in photothermal treatment planning, leveraging core-shell NPs for (pre)clinical applications, and enabling the easy addition of new functionalities through distinct ion doping.

Synthesis of Highly Luminescent Silica-Coated Upconversion Nanoparticles from Lanthanide Oxides or Nitrates Using Co-Precipitation and Sol-Gel Methods

Upconversion nanoparticles (UCNPs) are under consideration for their use as bioimaging probes with enhanced optical performance for real time follow-up under non-invasive conditions. Photostable and core-shell NaYF4:Yb3+, Er3+-SiO2 UCNPs obtained by a novel and simple co-precipitation method from lanthanide nitrates or oxides were herein synthesized for the first time. The sol-gel Stöber method followed by oven or supercritical gel drying was used to confer biocompatible surface properties to UCNPs by the formation of an ultrathin silica coating. Upconversion (UC) spectra were studied to evaluate the fluorescence of UCNPs upon red/near infrared (NIR) irradiation. ζ-potential measurements, TEM analyses, XRD patterns and long-term physicochemical stability were also assessed and confirmed that the UCNPs co-precipitation synthesis is a shape- and phase-controlling approach. The bio- and hemocompatibility of the UCNPs formulation with the highest fluorescence intensity was evaluated with murine fibroblasts and human blood, respectively, and provided excellent results that endorse the efficacy of the silica gel coating. The herein synthesized UCNPs can be regarded as efficient fluorescent probes for bioimaging purposes with the high luminescence, physicochemical stability and biocompatibility required for biomedical applications.

Recent advances in rare earth ion-doped upconversion nanomaterials: From design to their applications in food safety analysis

The misuse of chemicals in agricultural systems and food production leads to an increase in contaminants in food, which ultimately has adverse effects on human health. This situation has prompted a demand for sophisticated detection technologies with rapid and sensitive features, as concerns over food safety and quality have grown around the globe. The rare earth ion-doped upconversion nanoparticle (UCNP)-based sensor has emerged as an innovative and promising approach for detecting and analyzing food contaminants due to its superior photophysical properties, including low autofluorescence background, deep penetration of light, low toxicity, and minimal photodamage to the biological samples. The aim of this review was to discuss an outline of the applications of UCNPs to detect contaminants in food matrices, with particular attention on the determination of heavy metals, pesticides, pathogenic bacteria, mycotoxins, and antibiotics. The review briefly discusses the mechanism of upconversion (UC) luminescence, the synthesis, modification, functionality of UCNPs, as well as the detection principles for the design of UC biosensors. Furthermore, because current UCNP research on food safety detection is still at an early stage, this review identifies several bottlenecks that must be overcome in UCNPs and discusses the future prospects for its application in the field of food analysis.

Assessing the reproducibility and up-scaling of the synthesis of Er,Yb-doped NaYF4-based upconverting nanoparticles and control of size, morphology, and optical properties

Lanthanide-based, spectrally shifting, and multi-color luminescent upconverting nanoparticles (UCNPs) have received much attention in the last decades because of their applicability as reporter for bioimaging, super-resolution microscopy, and sensing as well as barcoding and anti-counterfeiting tags. A prerequisite for the broad application of UCNPs in areas such as sensing and encoding are simple, robust, and easily upscalable synthesis protocols that yield large quantities of UCNPs with sizes of 20 nm or more with precisely controlled and tunable physicochemical properties from low-cost reagents with a high reproducibility. In this context, we studied the reproducibility, robustness, and upscalability of the synthesis of β-NaYF₄:Yb, Er UCNPs via thermal decomposition. Reaction parameters included solvent, precursor chemical compositions, ratio, and concentration. The resulting UCNPs were then examined regarding their application-relevant physicochemical properties such as size, size distribution, morphology, crystal phase, chemical composition, and photoluminescence. Based on these screening studies, we propose a small volume and high-concentration synthesis approach that can provide UCNPs with different, yet controlled size, an excellent phase purity and tunable morphology in batch sizes of up to at least 5 g which are well suited for the fabrication of sensors, printable barcodes or authentication and recycling tags.

Recent advances in lanthanide-doped up-conversion probes for theranostics

Up-conversion (or anti-Stokes) luminescence refers to the phenomenon whereby materials emit high energy, short-wavelength light upon excitation at longer wavelengths. Lanthanide-doped up-conversion nanoparticles (Ln-UCNPs) are widely used in biomedicine due to their excellent physical and chemical properties such as high penetration depth, low damage threshold and light conversion ability. Here, the latest developments in the synthesis and application of Ln-UCNPs are reviewed. First, methods used to synthesize Ln-UCNPs are introduced, and four strategies for enhancing up-conversion luminescence are analyzed, followed by an overview of the applications in phototherapy, bioimaging and biosensing. Finally, the challenges and future prospects of Ln-UCNPs are summarized.

DUCNP@Mn-MOF/FOE as a Highly Selective and Bioavailable Drug Delivery System for Synergistic Combination Cancer Therapy

Heterostructures comprising lanthanide-doped upconversion nanoparticles (DUCNPs) and metal-organic frameworks (MOFs) are emerging as promising nanosystems for integrating medical diagnosis and treatment. Here, the DUCNP@Mn-MOF nanocarrier was developed, which showed good efficiency for loading and delivering a cytotoxic antitumor agent (3-F-10-OH-evodiamine, FOE). The combined advantages of the pH-responsive and peroxidase-like properties of Mn-MOF and the unique optical features of DUCNPs granted the DUCNP@Mn-MOF/FOE system synergistic chemodynamic and chemotherapeutic effects. The DUCNP@Mn-MOF nanocarrier effectively overcame the intrinsic limitations of FOE, such as its unfavorable physicochemical properties and limited in vivo potency. This complexed nanosystem was responsive to the tumor microenvironment and showed excellent tumor targeting capability. Thus, DUCNP@Mn-MOF/FOE exhibited highly selective and bioavailable drug delivery properties and is promising for cancer therapy. In a mouse breast cancer model, DUCNP@Mn-MOF/FOE inhibited tumor growth without significant toxicity. Therefore, the proposed nanosystem represents a promising theragnostic platform for multimodal combination diagnosis and therapy of tumors.

Applications of upconversion nanoparticles in analytical and biomedical sciences: a review

Lanthanide-doped upconversion nanoparticles (UCNPs) have gained more attention from researchers due to their unique properties of photon conversion from an excitation/incident wavelength to a more suitable emission wavelength at a designated site, thus improving the scope in the life sciences field. Due to their fascinating and unique optical properties, UCNPs offer attractive opportunities in theranostics for early diagnostics and treatment of deadly diseases such as cancer. Also, several efforts have been made on emerging approaches for the fabrication and surface functionalization of luminescent UCNPs in optical biosensing applications using various infrared excitation wavelengths. In this review, we discussed the recent advancements of UCNP-based analytical chemistry approaches for sensing and theranostics using a 980 nm laser as the excitation source. The key analytical merits of UNCP-integrated fluorescence analytical approaches for assaying a wide variety of target analytes are discussed. We have described the mechanisms of the upconversion (UC) process, and the application of surface-modified UCNPs for in vitro/in vivo bioimaging, photodynamic therapy (PDT), and photothermal therapy (PTT). Based on the latest scientific achievements, the advantages and disadvantages of UCNPs in biomedical and optical applications are also discussed to overcome the shortcomings and to improve the future study directions. This review delivers beneficial practical information of UCNPs in the past few years, and insights into their research in various fields are also discussed precisely.

Recent Progress of Rare Earth Doped Hydroxyapatite Nanoparticles: Luminescence Properties, Synthesis and Biomedical Applications

Hydroxyapatite nanoparticles (HAP NPs) are host materials and can be modified with various substrates and dopants. Among them, rare earth (RE) ions doped HAP NPs have gathered attention due to their unique physicochemical and imaging properties. Compared to other fluorescence probes, RE-doped HAP NPs display advantages in high brightness, high contrast, photostability, nonblinking, and narrow emission bands. Meanwhile, their intrinsic features (composition, morphology, size, crystallinity, and luminescence intensity) can be adjusted by changing the dopant ratio, synthesizing temperature, reaction time, and techniques. And they have been used in various biomedical applications, including imaging probe, drug delivery, bone tissue engineering, and antibacterial studies. This review surveys the luminescent properties, fluorescence enhancement, synthetic methods, and biocompatibility of various RE-doped HAP NPs consolidated from different research works, for their employments in biomedical applications. For this literature review, an electronic search was conducted in the Pubmed, Web of Science, Google Scholar, Scopus and SciFinder databases, using the keywords: hydroxyapatite, rare earth, lanthanide, fluorescence, and imaging. Literature searches of English-language publications from 1979 with updates through April, 2022, and a total of 472 potential papers were identified. In addition, a few references were located by noting their citation in other studies reviewed. STATEMENT OF SIGNIFICANCE: Hydroxyapatite nanoparticles (HAP NPs) have a broad range of promising biological applications. Although prospective biomedical applications are not limited to rare earth-doped hydroxyapatite nanoparticles (RE-doped HAP NPs), some cases do make use of the distinctive features of RE-elements to achieve the expected functions for HAP families. This review surveys the luminescent properties, synthetic methods, and biocompatibility of various RE-doped HAP NPs consolidated from different research works, for their employments in biomedical applications, including imaging probe, drug delivery, bone tissue repair and tracking, and anti-bacteria. Overall, we expect to shed some light on broadening the research and application of RE-doped HAP NPs in biomedical field.

Enhanced up-conversion photoluminescence in fluoride-oxyfluoride nanophosphor films by embedding gold nanoparticles

Owing to their unique non-linear optical character, lanthanide-based up-converting materials are potentially interesting for a wide variety of fields ranging from biomedicine to light harvesting. However, their poor luminescent efficiency challenges the development of technological applications. In this context, localized surface plasmon resonances (LSPRs) have been demonstrated as a valuable strategy to improve light conversion. Herein, we utilize LSPR induced by gold nanoparticles (NPs) to enhance up-conversion photoluminescence (UCPL) in transparent, i.e. scattering-free, films made of nanophosphors formed by fluoride-oxyfluoride host matrix that feature high thermal stability. Transparency allows excitation by an external source without extinction losses caused by unwanted diffuse reflection. We provide a simple method to embed gold NPs in films made of YF/YOF:Yb³⁺,Er³⁺ UC nanophosphors, via preparation of a viscous paste composed of both UC nanophosphors and colloidal gold NPs, reducing complexity in sample fabrication. The dimensions of gold NPs are such that their associated LSPR matches spectrally with the green emission band of the Er³⁺ doped nanophosphors. In order to demonstrate the benefits of plasmonic nanoparticles for UCPL in nanophosphor films, we provide a careful analysis of the structural properties of the composite thin films along with precise characterization of the impact of the gold NPs on the photophysical properties of UC nanophosphors.

Lanthanide-Doped Upconversion Luminescent Nanoparticles-Evolving Role in Bioimaging, Biosensing, and Drug Delivery

Upconverting luminescent nanoparticles (UCNPs) are "new generation fluorophores" with an evolving landscape of applications in diverse industries, especially life sciences and healthcare. The anti-Stokes emission accompanied by long luminescence lifetimes, multiple absorptions, emission bands, and good photostability, enables background-free and multiplexed detection in deep tissues for enhanced imaging contrast. Their properties such as high color purity, high resistance to photobleaching, less photodamage to biological samples, attractive physical and chemical stability, and low toxicity are affected by the chemical composition; nanoparticle crystal structure, size, shape and the route; reagents; and procedure used in their synthesis. A wide range of hosts and lanthanide ion (Ln3+) types have been used to control the luminescent properties of nanosystems. By modification of these properties, the performance of UCNPs can be designed for anticipated end-use applications such as photodynamic therapy (PDT), high-resolution displays, bioimaging, biosensors, and drug delivery. The application landscape of inorganic nanomaterials in biological environments can be expanded by bridging the gap between nanoparticles and biomolecules via surface modifications and appropriate functionalization. This review highlights the synthesis, surface modification, and biomedical applications of UCNPs, such as bioimaging and drug delivery, and presents the scope and future perspective on Ln-doped UCNPs in biomedical applications.

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.

Upconversion lanthanide nanomaterials: basics introduction, synthesis approaches, mechanism and application in photodetector and photovoltaic devices

Upconversion (UC) of lanthanide-doped nanostructure has the unique ability to convert low energy infrared (IR) light to high energy photons, which has significant potential for energy conversion applications. This review concisely discusses the basic concepts and fundamental theories of lanthanide nanostructures, synthesis techniques, and enhancement methods of upconversion for photovoltaic and for near-infrared (NIR) photodetector (PD) application. In addition, a few examples of lanthanide-doped nanostructures with improved performance were discussed, with particular emphasis on upconversion emission enhancement using coupling plasmon. The use of UC materials has been shown to significantly improve the NIR light-harvesting properties of photovoltaic devices and photocatalytic materials. However, the inefficiency of UC emission also prompted the need for additional modification of the optical properties of UC material. This improvement entailed the proper selection of the host matrix and optimization of the sensitizer and activator concentrations, followed by subjecting the UC material to surface-passivation, plasmonic enhancement, or doping. As expected, improving the optical properties of UC materials can lead to enhanced efficiency of PDs and photovoltaic devices.

Exploring the use of upconversion nanoparticles in chemical and biological sensors: from surface modifications to point-of-care devices

Upconversion nanoparticles (UCNPs) have emerged as promising luminescent nanomaterials due to their unique features that allow the overcoming of several problems associated with conventional fluorescent probes. Although UCNPs have been used in a broad range of applications, it is probably in the field of sensing where they best evidence their potential. UCNP-based sensors have been designed with high sensitivity and selectivity, for detection and quantification of multiple analytes ranging from metal ions to biomolecules. In this review, we deeply explore the use of UCNPs in sensing systems emphasizing the most relevant and recent studies on the topic and explaining how these platforms are constructed. Before diving into UCNP-based sensing platforms it is important to understand the unique characteristics of these nanoparticles, why they are attracting so much attention, and the most significant interactions occurring between UCNPs and additional probes. These points are covered over the first two sections of the article and then we explore the types of fluorescent responses, the possible analytes, and the UCNPs' integration with various material types such as gold nanostructures, quantum dots and dyes. All the topics are supported by analysis of recently reported sensors, focusing on how they are built, the materials' interactions, the involved synthesis and functionalization mechanisms, and the conjugation strategies. Finally, we explore the use of UCNPs in paper-based sensors and how these platforms are paving the way for the development of new point-of-care devices.

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.

Upconversion luminescent nanomaterials: A promising new platform for food safety analysis

Foodborne diseases have become a significant threat to public health worldwide. Development of analytical techniques that enable fast and accurate detection of foodborne pathogens is significant for food science and safety research. Assays based on lanthanide (Ln) ion-doped upconversion nanoparticles (UCNPs) show up as a cutting edge platform in biomedical fields because of the superior physicochemical features of UCNPs, including negligible autofluorescence, large signal-to-noise ratio, minimum photodamage to biological samples, high penetration depth, and attractive optical and chemical features. In recent decades, this novel and promising technology has been gradually introduced to food safety research. Herein, we have reviewed the recent progress of Ln³⁺-doped UCNPs in food safety research with emphasis on the following aspects: 1) the upconversion mechanism and detection principles; 2) the history of UCNPs development in analytical chemistry; 3) the in-depth state-of-the-art synthesis strategies, including synthesis protocols for UCNPs, luminescence, structure, morphology, and surface engineering; 4) applications of UCNPs in foodborne pathogens detection, including mycotoxins, heavy metal ions, pesticide residue, antibiotics, estrogen residue, and pathogenic bacteria; and 5) the challenging and future perspectives of using UCNPs in food safety research. Considering the diversity and complexity of the foodborne harmful substances, developing novel detections and quantification techniques and the rigorous investigations about the effect of the harmful substances on human health should be accelerated.

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.

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.

Controlled synthesis and upconversion luminescence properties of highly uniform and monodisperse β-NaYF4 :Yb3+ ,Tm3+ nanocrystals

Ytterbium, thulium (Yb³⁺ ,Tm³⁺ ) co-doped β-NaYF₄ upconversion nanocrystals (U-NCs) were synthesized by a convenient hydrothermal method using sodium citrate as a capping agent. X-ray diffraction (XRD) analysis revealed that NCs phase structures were dependent on reaction time. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results showed that the morphology of U-NCs could be controlled by adjusting the concentration of sodium citrate added in the hydrothermal reaction. Moreover, the emission spectra of the U-NCs were investigated to evaluate upconversion efficiency. Strong luminescence intensity of the U-NCs was observed after tuned with optimized concentration of sodium citrate. Furthermore, the U-NCs were incubated with MCF-7 cells at 37°C for 24 h. Under irradiation of a 980 nm laser, the upconversion blue emission of the NCs in MCF-7 cells can be clearly observed through a confocal microscope with an upconversion imaging system and high quality upconversion luminescence images can be acquired. Thus, prepared β-NaYF₄ :Yb³⁺ ,Tm³⁺ NCs provide us with highly efficient luminescent probes which can be applied for diverse bio-applications.

Study on cytotoxicity, cellular uptake and elimination of rare-earth-doped upconversion nanoparticles in human hepatocellular carcinoma cells

The growing use of rare-earth doped upconversion nanoparticles (UCNPs) has caused increasing concern about their biosafety. Here, to understand the toxicity of UCNPs and their mechanism in HepG2 cells, we systematically study the cytotoxicity, uptake and elimination behaviors of three types of UCNPs combined multiple cytotoxicity evaluation means with inductively coupled plasma mass spectrometry (ICP-MS) detection. Sodium yttrium fluoride, doped with 18% (molar ratio) ytterbium and 2% erbium (NaYF₄: Yb³⁺, Er³⁺) was selected as the model UCNPs with two sizes (35 and 55 nm), and the poly(acrylic acid) and polyethylenimine were selected as the representatives of negative and positive surface coating of UCNPs, respectively. UCNPs were found to induce cytotoxicity in time- and dose-dependent manners, which might be mediated by reactive oxygen species generation and oxidative stress. Apoptosis, inflammation, and metabolic process were enhanced after cells exposed to 200 mg/L UCNPs for 48 h. Increase in the protein levels of cleaved caspased-9, cleaved caspase-3 and Bax and decrease in the anti-apoptotic protein, Bcl-2 suggested that the mitochondria mediated pathway was involved in UCNP-induced apoptosis. With the aid of ICP-MS, it demonstrated that the cytotoxicity was associated with internalized amount of UCNPs, which largely relied on their surface properties rather than size in the tested range. By comparing UCNPs with Y³⁺ ions, it demonstrated that NPs properties played a nonnegligible role in the cytotoxicity of UCNPs. These findings provide new insights for fundamental understanding of cytotoxicity of UCNPs and may contribute to more rational use of these materials in the future.

Ex-vivo molecular imaging with upconversion nanoparticles (UCNPs) using photo thermal optical coherence tomography (PTOCT)

We demonstrate a photothermal optical coherence tomography (PTOCT) system, with upconversion nanoparticles (UCNPs) as a molecular probe. We synthesized hydrophilic, biocompatible upconversion nanoparticles (UCNPs) using hydrothermal synthesis. We developed the PTOCT system along with the signal processing tool and applied this technique on animal tissue phantom for targeted imaging. The 'lock-in detection' of the amplitude modulated photothermal beam (980 nm), which used to excite the UCNPs was the backbone of the signal processing algorithm. The signal processing was further established in different aspects. As an application part, the diffusion dynamics of the UCNPs was performed inside the tissue to study molecular movement and subsequent changes in tissue properties. A comparison of photothermal optical coherence tomography (PTOCT) with phase variance optical coherence tomography (PVOCT) for targeted molecular imaging also presented.

Photo-induced reactions for disassembling of coloaded photosensitizer and drug molecules from upconversion-mesoporous silica nanoparticles: An effective synergistic cancer therapy

Photodynamic therapy is an emerging noninvasive cancer treatment approach, which requires a photosensitizer (PS), light, and molecular oxygen. In this study, we have successfully fabricated a dual nature (pH- and reactive-oxygen-species-responsive) upconversion nanoparticles (UCNPs) to utilize coloaded doxorubicin (DOX) and chlorin e6 (Ce6) with high antitumor efficacy. The model anticancer drug (DOX) and PS (Ce6) were conjugated in a ratio of 1:1 (w:w), and then loaded on the surface of UCNPs@mesoporous silica (mSiO₂) (85.63 ± 9.87 nm). Cellular uptake could be achieved by either increased permeability or ionic effect of UCNPs@mSiO₂, where Ce6 controlled the DOX release under a near-infrared (NIR) laser irradiation at 980 nm. A cytotoxicity analysis revealed that the dual-responsive UCNPs@mSiO₂ could successfully deliver DOX and Ce6 at the tumor site, causing cell death with a high efficiency. This study shows that the modified UCNPs@mSiO₂ is a promising system to realize NIR-light-triggered PS and drug delivery approach to improve synergistic therapies in vitro and in vivo, in the future.