Yb³⁺/Er³⁺-Codoped Bi₂O₃ Nanospheres: Probe for Upconversion Luminescence Imaging and Binary Contrast Agent for Computed Tomography Imaging

Bismuth drug-inspired ultra-small dextran coated bismuth oxide nanoparticles for targeted computed tomography imaging of inflammatory bowel disease

Bismuth (Bi)-based computed tomography (CT) imaging contrast agents (CAs) hold significant promise for diagnosing gastrointestinal diseases due to their cost-effectiveness, heightened sensitivity, and commendable biocompatibility. Nevertheless, substantial challenges persist in achieving an easy synthesis process, remarkable water solubility, and effective targeting ability for the potential clinical transformation of Bi-based CAs. Herein, we show Bi drug-inspired ultra-small dextran coated bismuth oxide nanoparticles (Bi2O3-Dex NPs) for targeted CT imaging of inflammatory bowel disease (IBD). Bi2O3-Dex NPs are synthesized through a simple alkaline precipitation reaction using bismuth salts and dextran as the template. The Bi2O3-Dex NPs exhibit ultra-small size (3.4 nm), exceptional water solubility (over 200 mg mL-1), high Bi content (19.75 %), excellent biocompatibility and demonstrate higher X-ray attenuation capacity compared to clinical iohexol. Bi2O3-Dex NPs not only enable clear visualization of the GI tract outline and intestinal loop structures in CT imaging but also specifically target and accumulate at the inflammatory site in colitis mice after oral administration, facilitating a precise diagnosis and enabling targeted CT imaging of IBD. Our study introduces a novel and clinically promising strategy for synthesizing high-performance Bi2O3-Dex NPs for diagnosing gastrointestinal diseases.

X-ray activated near-infrared persistent luminescence nanoparticles for trimodality in vivo imaging

As promising luminescence nanoparticles, near-infrared (NIR) persistent luminescence nanoparticles (PLNPs) have received extensive attention in the field of high-sensitivity bioimaging in recent years. However, NIR PLNPs face problems such as short excitation wavelengths and single imaging modes, which limit their applications in in vivo reactivated imaging and multimodal imaging. Here, we report for the first time novel Gd2GaTaO7:Cr3+,Yb3+ (GGTO) NIR PLNPs that integrate X-ray activated NIR persistent luminescence (PersL), high X-ray attenuation and excellent magnetic properties into a single nanoparticle (NP). In this case, Cr3+ is used as the luminescence center. The co-doped Yb3+ and coating effectively enhance the X-ray activated NIR PersL. At the same time, the presence of the high-Z element Ta also makes the GGTO NPs exhibit high X-ray attenuation performance, which can be used as a CT contrast agent to achieve in vivo CT imaging. In addition, since the matrix contains a large amount of Gd, the GGTO NPs show remarkable magnetic properties, which can realize in vivo MR imaging. GGTO NPs combine the trimodal benefits of X-ray reactivated PersL, CT and MR imaging and are suitable for single or combined applications that require high sensitivity and spatial resolution imaging.

Metallic artifacts-free spectral computed tomography angiography based on renal clearable bismuth chelate

Computed tomography angiography (CTA) is one of the most important diagnosis techniques for various vascular diseases in clinic. However, metallic artifacts caused by metal implants and calcified plaques in more and more patients severely hinder its wide applications. Herein, we propose an improved metallic artifacts-free spectral CTA technique based on renal clearable bismuth chelate (Bi-DTPA dimeglumine) for the first time. Bi-DTPA dimeglumine owns the merits of ultra-simple synthetic process, approximately 100% of yield, large-scale production capability, good biocompatibility, and favorable renal clearable ability. More importantly, Bi-DTPA dimeglumine shows superior contrast-enhanced effect in CTA compared with clinical iohexol at a wide range of X-ray energies especially in higher X-ray energy. In rabbits' model with metallic transplants, Bi-DTPA dimeglumine assisted-spectral CTA can not only effectively mitigate metallic artifacts by reducing beam hardening effect under high X-ray energy, but also enables accurate delineation of vascular structure. Our proposed strategy opens a revolutionary way to solve the bottleneck problem of metallic artifacts in CTA examinations.

Near-Infrared-Responsive Rare Earth Nanoparticles for Optical Imaging and Wireless Phototherapy

Near-infrared (NIR) light is well-suited for the optical imaging and wireless phototherapy of malignant diseases because of its deep tissue penetration, low autofluorescence, weak tissue scattering, and non-invasiveness. Rare earth nanoparticles (RENPs) are promising NIR-responsive materials, owing to their excellent physical and chemical properties. The 4f electron subshell of lanthanides, the main group of rare earth elements, has rich energy-level structures. This facilitates broad-spectrum light-to-light conversion and the conversion of light to other forms of energy, such as thermal and chemical energies. In addition, the abundant loadable and modifiable sites on the surface offer favorable conditions for the functional expansion of RENPs. In this review, the authors systematically discuss the main processes and mechanisms underlying the response of RENPs to NIR light and summarize recent advances in their applications in optical imaging, photothermal therapy, photodynamic therapy, photoimmunotherapy, optogenetics, and light-responsive drug release. Finally, the challenges and opportunities for the application of RENPs in optical imaging and wireless phototherapy under NIR activation are considered.

Achieving Orthogonal Upconversion Luminescence of a Single Lanthanide Ion in Crystals for Optical Encryption

Optical encryption shows great potential in meeting the growing demand for advanced anti-counterfeiting in the information age. The development of upconversion luminescence (UCL) materials capable of emitting different colors of light in response to different external stimuli holds great promise in this field. However, the effective realization of multicolor UCL materials usually requires complex structural designs. In this work, orthogonal UCL is achieved in crystals with a simple structure simply by introducing modulator Tm3+ ions to control the photon transition processes between different energy levels of activator Er3+ ions. The obtained crystals emit red and green UCL when excited by 980 nm and 808 nm lasers, respectively. The orthogonal excitation-emission properties of crystals are shown to be very suitable for high-level optical encryption, which is important for information security and anti-counterfeiting. This work provides an effective strategy for obtaining orthogonal UCL in simple structural materials, which will encourage researchers to further explore novel orthogonal UCL materials and their applications, and has important implications for the development of the frontier photonic upconversion fields.

Hollow nanoparticles synthesized via Ostwald ripening and their upconversion luminescence-mediated Boltzmann thermometry over a wide temperature range

Upconversion nanoparticles (UCNPs) with hollow structures exhibit many fascinating optical properties due to their special morphology. However, there are few reports on the exploration of hollow UCNPs and their optical applications, mainly because of the difficulty in constructing hollow structures by conventional methods. Here, we report a one-step template-free method to synthesize NaBiF₄:Yb,Er (NBFYE) hollow UCNPs via Ostwald ripening under solvothermal conditions. Moreover, we also elucidate the possible formation mechanism of hollow nanoparticles (HNPs) by studying the growth process of nanoparticles in detail. By changing the contents of polyacrylic acid and H₂O in the reaction system, the central cavity size of NBFYE nanoparticles can be adjusted. Benefiting from the structural characteristics of large internal surface area and high surface permeability, NBFYE HNPs exhibit excellent luminescence properties under 980 nm near-infrared irradiation. Importantly, NBFYE hollow UCNPs can act as self-referenced ratiometric luminescent thermometers under 980 nm laser irradiation, which are effective over a wide temperature range from 223 K to 548 K and have a maximum sensitivity value of 0.0065 K^-1 at 514 K. Our work clearly demonstrates a novel method for synthesizing HNPs and develops their applications, which provides a new idea for constructing hollow structure UCNPs and will also encourage researchers to further explore the optical applications of hollow UCNPs.

Modulating electron population pathways for time-dependent dynamic multicolor displays

Multicolor luminescent nanoparticles (NPs) show several potential emerging applications. In this work, we provide a new route that integrates the afterglow and upconversion (UC) that originate in a single activator to achieve color variations without the modulation of any other parameters. The Er³⁺ ions in Na₃HfF₇:Yb/Er NPs exhibit bright green afterglow upon X-ray irradiation and single-band red UC under 980 nm laser excitation, which are attributed to the significantly different electron population pathways. The UC intensity is stable and the afterglow decreases gradually over time, thus the output color is clearly changed from green to red naturally via illuminating the pre-X-ray-irradiated NPs with a 980 nm laser. Furthermore, the fine emission profiles of Er³⁺, Ho³⁺ and Tm³⁺ are achieved upon X-ray irradiation. Our results develop a new approach for time-dependent dynamic color displays and a simple route to revealing the electronic fine structures of lanthanide activators at room temperature.

Linear red/green ratiometric thermometry of Ho3+/Cr3+ co-doped red up-conversion tungstate materials

Existing optical thermometers are faced with the challenges of high sensitivity limited to a very narrow high temperature range, while also lacking low temperature sensing performance. A new linear up-conversion (UC) optical thermometer with high sensitivity over a wide temperature range was reported here. The introduction of Cr³⁺ optimized the red-green (R/G) ratio and improved the temperature sensing characteristics of Ho³⁺-doped tungstate materials. Notably, as a temperature-related parameter, the R/G emission intensity ratio of Ho³⁺/Cr³⁺ co-doped tungstate material fitted well linearly with temperature. The slope of the fitted line corresponded to the absolute sensitivity value; that is, the sensitivity was constantly 0.0217 K^-1 over the wide range of 163-663 K. This new UC temperature sensor with high sensitivity extended a new field of optical temperature measurement and demonstrated the possibility of applying this linear sensitivity effect in sensing applications. Most importantly, from an optical temperature sensing point of view, this study provided a novel and effective strategy for linear optical temperature measurement.

Facile Fabrication of BiF3: Ln (Ln = Gd, Yb, Er)@PVP Nanoparticles for High-Efficiency Computed Tomography Imaging

X-ray computed tomography (CT) has been widely used in clinical practice, and contrast agents such as Iohexol are often used to enhance the contrast of CT imaging between normal and diseased tissue. However, such contrast agents can have some toxicity. Thus, new CT contrast agents are urgently needed. Owing to the high atomic number (Z = 83), low cost, good biological safety, and great X-ray attenuation property (5.74 cm² kg^-1 at 100 keV), bismuth has gained great interest from researchers in the field of nano-sized CT contrast agents. Here, we synthesized BiF₃: Ln@PVP nanoparticles (NPs) with an average particle size of about 380 nm. After coating them with polyvinylpyrrolidone (PVP), the BiF₃: Ln@PVP NPs possessed good stability and great biocompatibility. Meanwhile, compared with the clinical contrast agent Iohexol, BiF₃: Ln@PVP NPs showed superior in vitro CT imaging contrast. Subsequently, after in situ injection with BiF₃: Ln@PVP NPs, the CT value of the tumor site after the injection was significantly higher than that before the injection (the CT value of the pre-injection and post-injection was 48.9 HU and 194.58 HU, respectively). The morphology of the gastrointestinal (GI) tract can be clearly observed over time after oral administration of BiF₃: Ln@PVP NPs. Finally, the BiF₃: Ln@PVP NPs were completely discharged from the GI tract of mice within 48 h of oral administration with no obvious damage to the GI tract. In summary, our easily synthesized BiF₃: Ln@PVP NPs can be used as a potential clinical contrast agent and may have broad application prospects in CT imaging.

Progress in the therapeutic applications of polymer-decorated black phosphorus and black phosphorus analog nanomaterials in biomedicine

Wonderful black phosphorus (BP) and some BP analogs (BPAs) have been increasingly studied for their biomedical applications owing to their fascinating properties and biodegradability, but opportunities and challenges have always coexisted in their study. Poor stability upon exposure to the natural environment is the major obstacle hampering their in vivo applications. BP/polymer and BPAs/polymer nanocomposites can not only efficiently prevent their oxidation and aggregation but also exhibit "biological activity" due to synergistic effects. In this review, we briefly describe the synthesis methods and stability strategies of BP/polymer and BPAs/polymer. Then, advances pertaining to their exciting therapeutic applications in various fields are systematically introduced, such as cancer therapy (phototherapy, drug delivery, and synergistic immunotherapy), bone regeneration, and neurogenesis. Some challenges for future clinical trials and possible directions for further study are finally discussed.

Photothermometric analysis of bismuth ions using aggregation-induced nanozyme system with a target-triggered surface cleaning effect

The development of nanozyme-based photothermometric sensing for point-of-care testing (POCT) heavy metal ions is of great significance for disease diagnosis and health management. Considering the low catalytic activity of most nanozymes at physiological pH, we found bismuth ions (Bi³⁺) could effectively enhance the peroxidase (POX)-like activity of cetyltrimethylammonium bromide and citrate-capped octahedral gold nanoparticle (CTAB/Cit-AuNP) nanozymes. It is mainly based on Bi³⁺ ions being able to trigger the surface cleaning effect of CTAB/Cit-AuNPs. Because the more active Bi³⁺ ions could effectively bind with citrate on the gold surface and competitively destroy the electrostatic interaction between citrate and CTAB, resulting in the removal of CTAB ligands from the gold surface. Without the ligand protection, CTAB/Cit-AuNPs aggregated immediately, and further resulted in a significant activation of the POX-like activity of AuNP nanozymes. Based on this principle, we introduced the enzyme substrate 3,3',5,5'-tetramethylbenzidine (TMB) into this aggregation-induced nanozyme system, and rationally designed a photothermometric platform to quickly and sensitively detect Bi³⁺ ions by using the good photothermal effect of the oxidation product of TMB (oxTMB). The developed photothermometric method only using a common thermometer has a limit of detection (LOD) as low as 45.7 nM for POCT analysis of Bi³⁺ ions. This study not only provides a more accurate understanding of the aggregation-induced nanozymes based on the surface cleaning principle, but also shows the potential applications of aggregation-induced nanozymes in the POCT field.

BiVO4/Fe3O4@polydopamine superparticles for tumor multimodal imaging and synergistic therapy

Background

Despite tremendous progress has been achieved in tumor theranostic over the past decade, accurate identification and complete eradication of tumor cells remain a great challenge owing to the limitation of single imaging modality and therapeutic strategy.

Results

Herein, we successfully design and construct BiVO₄/Fe₃O₄@polydopamine (PDA) superparticles (SPs) for computed tomography (CT)/photoacoustic (PA)/magnetic resonance (MR) multimodal imaging and radiotherapy (RT)/photothermal therapy (PTT) synergistic therapy toward oral epithelial carcinoma. On the one hand, BiVO₄ NPs endow BiVO₄/Fe₃O₄@PDA SPs with impressive X-ray absorption capability due to the high X-ray attenuation coefficient of Bi, which is beneficial for their utilization as radiosensitizers for CT imaging and RT. On the other hand, Fe₃O₄ NPs impart BiVO₄/Fe₃O₄@PDA SPs with the superparamagnetic property as a T₂-weighted contrast agent for MR imaging. Importantly, the aggregation of Fe₃O₄ NPs in SPs and the presence of PDA shell greatly improve the photothermal conversion capability of SPs, making BiVO₄/Fe₃O₄@PDA SPs as an ideal photothermal transducer for PA imaging and PTT. By integrating advantages of various imaging modalities (CT/PA/MR) and therapeutic strategies (RT/PTT), our BiVO₄/Fe₃O₄@PDA SPs exhibit the sensitive multimodal imaging feature and superior synergistic therapeutic efficacy on tumors.

Conclusions

Since there are many kinds of building blocks with unique properties appropriating for self-assembly, our work may largely enrich the library of nanomateirals for tumor diagnosis and treatment.

Pnictogen Semimetal (Sb, Bi)-Based Nanomaterials for Cancer Imaging and Therapy: A Materials Perspective

Innovative multifunctional nanomaterials have attracted tremendous interest in current research by facilitating simultaneous cancer imaging and therapy. Among them, antimony (Sb)- and bismuth (Bi)-based nanoparticles are important species with multifunction to boost cancer theranostic efficacy. Despite the rapid development, the extensive previous work treated Sb- and Bi-based nanoparticles as mutually independent species, and therefore a thorough understanding of their relationship in cancer theranostics was lacking. We propose here that the identical chemical nature of Sb and Bi, being semimetals, provides their derived nanoparticles with inherent multifunction for near-infrared laser-driven and/or X-ray-based cancer imaging and therapy as well as some other imparted functions. An overview of recent progress on Sb- and Bi-based nanoparticles for cancer theranostics is provided to highlight the relationship between chemical nature and multifunction. The understanding of Sb- and Bi-based nanoparticles in this way might shed light on the further design of smart multifunctional nanoparticles for cancer theranostics.

Rapid aqueous-phase synthesis of highly stable K0.3Bi0.7F2.4 upconversion nanocrystalline particles at low temperature

Lanthanide-doped K_0.3Bi_0.7F_2.4 nanocrystalline particles are synthesized through an ultrafast (only 1 min) and aqueous-phase chemical method at low temperature (room temperature ∼ 90 °C), which can be used as pigments for anti-counterfeiting.

Integration of IR-808 and thiol-capped Au–Bi bimetallic nanoparticles for NIR light mediated photothermal/photodynamic therapy and imaging

A novel Au–Bi bimetallic nanoplatform has been developed for enhanced photodynamic and photothermal therapy.

Construction of thiol-capped ultrasmall Au-Bi bimetallic nanoparticles for X-ray CT imaging and enhanced antitumor therapy efficiency

Thiol capped gold nanoparticles with small size, high dispersity, and broad light absorption covering ultraviolet (UV) to near infrared (NIR) region have been developed for catalysis, fluorescence imaging and photodynamic therapy (PDT). The constitution of the metal core in such nanoparticles can strongly influence the luminescence, catalysis, and stability properties. However, to date, a corresponding investigation of the influence of the metallic core on the generation of reaction oxygen species (ROS) and its therapeutic efficiency towards tumor cells remains to be lacking. Herein, we fabricated bimetallic nanoparticles by introducing bismuth into captopril capped gold nanoparticles. Surprisingly, the introduction of the Bi was found enhance the photothermal effect of the nanoparticles to a great extent, and the variation trends for the thermal effect, ROS generation rate, and tumor cell inhibition effect were found to disparate with the changes in the Au and Bi composition. The origin of the photothermal effect was deduced through density functional theory calculations based on microscopic construction. Combined with the intrinsic photodynamic effect, the bimetallic nanoparticles showed an outstanding tumor cell inhibition effect. Furthermore, due to the excellent CT imaging property, our designed nanoparticles provide the exciting possibility to realize CT imaging guided and light-mediated tumor therapy.

A Review on the Biodistribution, Pharmacokinetics and Toxicity of Bismuth-Based Nanomaterials

Here, bismuth-based nanomaterials (Bi-based NMs) are introduced as promising theranostic agents to enhance image contrast as well as for the therapeutic gain for numerous diseases. However, understanding the interaction of such novel developed nanoparticles (NPs) within a biological environment is a requisite for the translation of any promising agent from the lab bench to the clinic. This interaction delineates the fate of NPs after circulation in the body. In an ideal setting, a nano-based therapeutic agent should be eliminated via the renal clearance pathway, meanwhile it should have specific targeting to a diseased organ to reach an effective dose and also to overcome off-targeting. Due to their clearance pathway, biodistribution patterns and pharmacokinetics (PK), Bi-based NMs have been found to play a determinative role to pass clinical approval and they have been investigated extensively in vivo to date. In this review, we expansively discuss the possible toxicity induced by Bi-based NMs on cells or organs, as well as biodistribution profiles, PK and the clearance pathways in animal models. A low cytotoxicity of Bi-based NMs has been found in vitro and in vivo, and along with their long-term biodistribution and proper renal clearance in animal models, the translation of Bi-based NMs to the clinic as a useful novel theranostic agent is promising to improve numerous medical applications.

Fabrication of Er3+/Yb3+ Co-Doped Bi5O7I Microsphere With Upconversion Luminescence and Enhanced Photocatalytic Activity for Bisphenol A Degradation

Er3+/Yb3+ co-doped Bi5O7I uniform porous microsphere photocatalysts were synthesized by a two-step chemical method, which possesses excellent photocatalytic performance and upconversion luminescence property. The photocatalytic performance of the photocatalysts was studied by degradation of bisphenol A in aqueous solution under visible light and different monochromatic light irradiation. The photocatalytic performance of Er3+/Yb3+ co-doped Bi5O7I sample is better than that of the pristine Bi5O7I and Er3+-doped Bi5O7I samples. Moreover, Er3+/Yb3+ co-doped Bi5O7I possesses photocatalytic ability with a red light monochromatic LED lamp (3 W, λ = 630 nm) and an infrared monochromatic LED lamp (100 W, λ = 940 nm) irradiation whose wavelength is longer than the absorption-limiting wavelength of pristine Bi5O7I sample. This phenomenon further verified that the upconversion property of Er3+ and Yb3+ causes the improved photocatalytic efficiency of Er3+/Yb3+ co-doped Bi5O7I sample.

X-ray and NIR light dual-triggered mesoporous upconversion nanophosphor/Bi heterojunction radiosensitizer for highly efficient tumor ablation

Developing a multi-functional radiosensitizer with high efficiency and low toxicity remains challenging. Herein, we report a mesoporous heterostructure radiosensitizer (UCNP@NBOF-FePc-PFA) containing Lu-based upconversion nanophosphor (UCNP) and Bi-based nanomaterial loaded with iron phthalocyanine for X-ray and NIR light dual-triggered tri-modal tumor therapy. NaLuF₄:Yb,Tm, a Lu-based UCNP, offers radiosensitization and upconversion luminescence for optical bio-imaging. However, Bi has a higher X-ray mass attenuation coefficient than Lu. Thus, after stepwise fabrication, Na_0.2Bi_0.8O_0.35F_1.91:Yb (NBOF) was assembled with the UCNP to form a mesoporous heterostructure composite. This enhanced the radiosensitization effect and drug load to realize multi-modal tumor therapy. After coating it with folate-conjugated amphiphilic PEG (PFA), UCNP@NBOF-FePc-PFA realized tumor photothermal/photodynamic/radio-therapy. The structure of UCNP@NBOF-FePc-PFA was well characterized. Different properties triggered by X-ray and NIR light were evaluated. Finally, a highly efficient tumor ablation effect was demonstrated in vitro and in vivo. Consequently, this kind of nanocomposite provides a unique strategy for designing a theranostic platform for oncotherapy. STATEMENT OF SIGNIFICANCE: The synergy of enhanced radiotherapy and photothermal/photodynamic therapy is found to improve tumor therapeutic efficacy. On that basis, a heterostructure nanohybrid containing Lu-based UCNP and Bi-based mesoporous material is synthesized. The heterostructure nanohybrid can be loaded with FePc and decorated with folate-modified amphiphilic PEG to form a multi-functional theranostic nano-platform. The platform exhibits upconversion luminescence capacity, X-ray attenuation property, photothermal effect, and X-ray and NIR dual-light triggered ROS generation capability. These features can not only enable upconversion luminescence/CT bioimaging of living beings but also be applied to the photothermal/photodynamic/radio- synergistic tumor ablation. To sum up, the nanomaterial offers a novel method for the construction of a new theranostic platform.

The versatile biomedical applications of bismuth-based nanoparticles and composites: therapeutic, diagnostic, biosensing, and regenerative properties

Studies of nanosized forms of bismuth (Bi)-containing materials have recently expanded from optical, chemical, electronic, and engineering fields towards biomedicine, as a result of their safety, cost-effective fabrication processes, large surface area, high stability, and high versatility in terms of shape, size, and porosity. Bi, as a nontoxic and inexpensive diamagnetic heavy metal, has been used for the fabrication of various nanoparticles (NPs) with unique structural, physicochemical, and compositional features to combine various properties, such as a favourably high X-ray attenuation coefficient and near-infrared (NIR) absorbance, excellent light-to-heat conversion efficiency, and a long circulation half-life. These features have rendered bismuth-containing nanoparticles (BiNPs) with desirable performance for combined cancer therapy, photothermal and radiation therapy (RT), multimodal imaging, theranostics, drug delivery, biosensing, and tissue engineering. Bismuth oxyhalides (BiO_x, where X is Cl, Br or I) and bismuth chalcogenides, including bismuth oxide, bismuth sulfide, bismuth selenide, and bismuth telluride, have been heavily investigated for therapeutic purposes. The pharmacokinetics of these BiNPs can be easily improved via the facile modification of their surfaces with biocompatible polymers and proteins, resulting in enhanced colloidal stability, extended blood circulation, and reduced toxicity. Desirable antibacterial effects, bone regeneration potential, and tumor growth suppression under NIR laser radiation are the main biomedical research areas involving BiNPs that have opened up a new paradigm for their future clinical translation. This review emphasizes the synthesis and state-of-the-art progress related to the biomedical applications of BiNPs with different structures, sizes, and compositions. Furthermore, a comprehensive discussion focusing on challenges and future opportunities is presented.

Yolk–shell structured Bi2SiO5:Yb3+,Ln3+ (Ln = Er, Ho, Tm) upconversion nanophosphors for optical thermometry and solid-state lighting

Bi₂SiO₅:Yb³⁺,Er³⁺ yolk–shell nanophosphors have been successfully synthesized, which are expected to find important applications in optical thermometry and solid-state lighting.

Room-temperature ultrafast synthesis, morphology and upconversion luminescence of K0.3Bi0.7F2.4:Yb3+/Er3+ nanoparticles for temperature-sensing application

This manuscript describes an ultrafast route at room temperature for the synthesis of the K_0.3Bi_0.7F_2.4 nanoparticles with photoluminescence and luminescent temperature sensing.

Lanthanide-doped bismuth-based fluoride nanoparticles: controlled synthesis and ratiometric temperature sensing

Controllable NaBiF₄ nanoparticles have been synthesized through Gd³⁺ doping for ratiometric temperature sensing in a wide range.

Ultrafast Synthesizing Bismuth Mesoporous Nanolitchi Radiosensitizer Loading High Dose DOX for CT-Guided Enhanced Chemoradiotherapy

Radiotherapy and chemotherapy are both common clinical treatment methods. The combination of the two treatments can decrease tumor recurrence. In this study, bismuth-based mesoporous litchi-shaped Na_0.2Bi_0.8O_0.35F_1.91:20%Yb (NBOF) nanoparticles (NPs) have been reported as a radiosensitizer and as a nanovehicle for loading and slow-releasing doxorubicin (DOX). After assembling with amphiphilic poly(ethylene glycol) (PEG), NBOF-DOX-PEG qualified with excellent aqueous dispersibility and the enhanced tumor radiation and chemo-synergistic therapy characteristics. The formation of NBOF revealed the oxygen element in NBOF came from H₂O and air in the synthesis and post-treatment process, and the size of NBOF could be adjusted by changing the concentration of doped Yb ion. The average size of NBOF was ca. 80 nm. Brunauer-Emmett-Teller results demonstrated the mesoporous structure of NBOF. So DOX could be loaded in NBOF and the optimized loading content was 39%. Then, NBOF-PEG exhibited a strong computed tomography signal whitening ability and enhanced radiotherapy effect. Combined with the chemotherapy ability of DOX, NBOF-DOX-PEG NPs presented remarkable synergistic tumor elimination ability. Meanwhile, NBOF-DOX-PEG NPs qualified for excellent biosafety. Our study not only proved the combined chemo- and radiotherapy for enhancing therapeutic effect but also supplied a functional Bi-based mesoporous nanovehicle for constructing an intelligent theranostic platform.

Facile Aqueous-Phase Synthesis of an Ultrasmall Bismuth Nanocatalyst for the Reduction of 4-Nitrophenol

Bismuth metallic nanoparticles have evoked considerable interest in catalysis owing to their small size, high surface area-to-volume ratio, and low toxicity. However, the need for toxic reductants and organic solvents in their synthesis often limits their desirability for application development. Here, we describe a green strategy to synthesize bismuth nanodots via the redox reactions between bismuth nitrate and d-glucose, in the presence of poly(vinylpyrrolidone) in the basic aqueous phase. Both reagents play a crucial role in the formation of monodisperse bismuth nanodots acting as mild reducing and capping agents, respectively. We further demonstrate that the catalytic activity of these dots via the successful reduction of the environmental contaminant 4-nitrophenol to its useful 4-aminophenol analogue requiring only 36 μg/mL nanocatalyst for 20 mM of the substrate. Moreover, they can be recovered and recycled in multiple reactions before the onset of an appreciable loss of catalytic activity. The proposed facile synthetic route and inexpensive matrix materials lead the way to access bismuth nanodots for both the fundamental study of reactions and their industrial catalysis applications.

Designing of UCNPs@Bi@SiO2 Hybrid Theranostic Nanoplatforms for Simultaneous Multimodal Imaging and Photothermal Therapy

Herein, a novel multifunctional nanoplatform was designed toward multimodality imaging and photothermal therapy (PTT). It was found that Bi nanoparticles could grow in situ on the surface of NaYF₄:20%Yb,2%Er@NaYF₄:40%Yb@NaGdF₄ core-shell nanoparticles (labeled as UCNPs). In this structure, UCNPs were mainly employed as an upconversion luminescence (UCL) imaging agent, whereas the Bi nanoparticles worked as an effective CT imaging and photothermal agent. Importantly, a dense SiO₂ shell was employed to protect the Bi nanoparticles from oxidation, and it also endowed the nanoplatform with excellent hydrophilic ability. The effective UCL/CT imaging and PTT performances were emphasized by a series of in vivo experiments, which suggest that the integrated nanoplatform with imaging and therapy functions shows great promise in the biomedical field.

Bi2SiO5@g-SiO2 upconverting nanoparticles: a bismuth-driven core-shell self-assembly mechanism

Core-shell systems have attracted increasing interest among the research community in recent years due to their unique properties and structural features, and the development of new synthetic strategies is still a challenge. In this work, we have investigated lanthanide-doped Bi2SiO5 nanocrystal formation inside mesoporous silica nanoparticles (MSNs). The role of both synthesis temperature and concentration of the bismuth precursor impregnated into the MSNs is discussed, showing an unprecedented strategy for the simultaneous stabilization of a crystalline core and a glassy shell. Temperature dependent synchrotron radiation X-ray powder diffraction (SR-XRPD) and high resolution transmission electron microscopy (HR-TEM) analyses allow one to follow the crystalline core growth. A mechanism for the formation of a Bi2SiO5@g-SiO2 core-shell nanosystem is proposed. In addition, the easy tunability of the color output of the upconverting system is demonstrated by means of suitable doping lanthanide ions with potential applications in several fields.

Multifunctional BiF3:Ln3+ (Ln = Ho, Er, Tm)/Yb3+ nanoparticles: an investigation on the emission color tuning, thermosensitivity, and bioimaging

Pure cubic phase and uniform BiF₃:Ln³⁺ (Ln = Ho, Er, Tm)/Yb³⁺ nanoparticles (NPs) were prepared by coprecipitation. The growth mechanism of BiF₃:2%Er³⁺/20%Yb³⁺ NPs was proposed based on evolution analysis of the time-dependent morphology, in which BiF₃:2%Er³⁺/20%Yb³⁺ was formed through the growth process of “nucleation to crystallization and Ostwald ripening”. The upconversion luminescence (UCL) properties and mechanism of BiF₃:Ln³⁺ (Ln = Ho, Er, Tm)/Yb³⁺ under dual-wavelength excitation were also systematically investigated. The emission intensity of BiF₃:2%Er³⁺/20%Yb³⁺ by dual-wavelength excitation (λ = 980 nm + 1550 nm) was 1.49 times more than that excited by 1550 nm or 980 nm individually. Furthermore, the properties of the bright white and multicolor UCL showed that yellow, purple, green, or pinkish light could be observed by controlling the doping concentration of Ln³⁺ (Ln = Yb, Er, Tm, and Ho), indicating that they had potential applications in backlight sources of color displays and security labeling. The temperature sensitivity of BiF₃:2%Er³⁺/20%Yb³⁺ exhibited a downward tendency and its max value was about 0.0036 K⁻¹ at 273 K. Cell toxicity tests showed that the UCNPs in phospholipid aqueous solution presented low cytotoxicity. Also, in vivo imaging and X-ray imaging revealed that the BiF₃:2%Er³⁺/20%Yb³⁺ NPs had deep penetration and high contrast, which meant it could be used as a potential probe and contrast agent in in vivo optical bioimaging.

Multifunctional BiF₃:Ln³⁺(Ln = Ho, Er, Tm)/Yb³⁺ UCLNPs presented better performances in dual-wavelength synergy, thermosensitivity, emission color tuning, and bioimaging.

Ultrafast synthesis of ultrasmall polyethylenimine-protected AgBiS2 nanodots by "rookie method" for in vivo dual-modal CT/PA imaging and simultaneous photothermal therapy

Developing a biocompatible nanotheranostic platform integrating diagnostic and therapeutic functions is a great prospect for cancer treatment. However, it is still a great challenge to synthesize nanotheranostic agents using an ultra-facile method. In the research reported here, ultrasmall polyethylenimine-protected silver bismuth sulfide (PEI-AgBiS2) nanodots were successfully synthesized using an ultra-facile and environmentally friendly strategy (1 min only at room temperature), which could be described as a "rookie method". PEI-AgBiS2 nanodots show good monodispersity and biocompatibility. For the first time, PEI-AgBiS2 nanodots were reported as a powerful and safe nanotheranostic agent for cancer treatment. PEI-AgBiS2 nanodots exhibit excellent computed tomography (CT) and photoacoustic (PA) dual-modal imaging ability, which could effectively guide photothermal cancer therapy. Furthermore, PEI-AgBiS2 nanodots exhibit a high photothermal conversion efficiency (η = 35.2%). The photothermal therapy (PTT) results demonstrated a highly efficient tumor ablation ability. More importantly, the blood biochemistry and histology analyses verify that the PEI-AgBiS2 nanodots have negligible long-term toxicity. This work highlights that PEI-AgBiS2 nanodots produced using this extremely effective method are a high-performance and safe PTT agent. These findings open a new gateway for synthesizing nanotheranostic agents by using this ultra-facile method in the future.

Three-dimensional angiography fused with CT/MRI for multimodal imaging of nanoparticles based on Ba4Yb3F17:Lu3+,Gd3+

Designing nanosized multi-modality contrast agents for high-resolution imaging is challenging since most agents are only useful for single-mode imaging. In this work, we successfully synthesized biocompatible polyethylene glycol (PEG-) and l-glutamine (GLN-) modified Ba4Yb3F17:Lu3+,Gd3+ nanoparticles (LNPs@PEG@GLN) that can be employed as a multi-modality contrast agent. Fluorescence dye-modified LNPs@PEG@GLN nanoparticles can be used for computed tomography (CT), magnetic resonance imaging (MRI), and fluorescence imaging (FI). They display high X-ray absorption, outstanding T2-weighted imaging capability, and good fluorescence uptake. Furthermore, LNPs@PEG@GLN enhances contrast efficiencies for different imaging modalities in vivo. Interestingly, LNPs@PEG@GLN is a promising agent for CT angiography. These nanoparticles could be a promising contrast agent for multi-modality imaging and diagnosing vascular diseases.

Rare-earth Nanoparticle-induced Cytotoxicity on Spatial Cognition Memory of Mouse Brain

Background:

Luminescent rare-earth-based nanoparticles have been increasingly used in nanomedicine due to their excellent physicochemical properties, such as biomedical imaging agents, drug carriers, and biomarkers. However, biological safety of the rare-earth-based nanomedicine is of great significance for future development in practical applications. In particular, biological effects of rare-earth nanoparticles on human's central nervous system are still unclear. This study aimed to investigate the potential toxicity of rare-earth nanoparticles in nervous system function in the case of continuous exposure.

Methods:

Adult ICR mice were randomly divided into seven groups, including control group (receiving 0.9% normal saline) and six experimental groups (10 mice in each group). Luminescent rare-earth-based nanoparticles were synthesized by a reported co-precipitation method. Two different sizes of the nanoparticles were obtained, and then exposed to ICR mice through caudal vein injection at 0.5, 1.0, and 1.5 mg/kg body weight in each day for 7 days. Next, a Morris water maze test was employed to evaluate impaired behaviors of their spatial recognition memory. Finally, histopathological examination was implemented to study how the nanoparticles can affect the brain tissue of the ICR mice.

Results:

Two different sizes of rare-earth nanoparticles have been successfully obtained, and their physical properties including luminescence spectra and nanoparticle sizes have been characterized. In these experiments, the rare-earth nanoparticles were taken up in the mouse liver using the magnetic resonance imaging characterization. Most importantly, the experimental results of the Morris water maze tests and histopathological analysis clearly showed that rare-earth nanoparticles could induce toxicity on mouse brain and impair the behaviors of spatial recognition memory. Finally, the mechanism of adenosine triphosphate quenching by the rare-earth nanoparticles was provided to illustrate the toxicity on the mouse brain.

Conclusions:

This study suggested that long-term exposure of high-dose bare rare-earth nanoparticles caused an obvious damage on the spatial recognition memory in the mice.

Near-infrared optical and X-ray computed tomography dual-modal imaging probe based on novel lanthanide-doped K0.3Bi0.7F2.4 upconversion nanoparticles

A novel K_0.3Bi_0.7F_2.4 upconversion (UC) matrix has been prepared successfully by a solvothermal method. K_0.3Bi_0.7F_2.4:Yb³⁺/Ln³⁺ (Ln = Er, Ho, Tm) upconversion nanoparticles (UCNPs) show a corresponding excellent upconversion luminescence (UCL) under 980 nm laser irradiation. Especially, the strong near-infrared (NIR) UCL of K_0.3Bi_0.7F_2.4:20% Yb³⁺/0.5% Tm³⁺ (abbreviated as BYT) UCNPs is suitable for deep tissue optical imaging. Moreover, the high X-ray absorption coefficient of Bi makes the as-prepared UCNPs favorable for computed tomography (CT) imaging. The citrate-coated BYT UCNPs show good biocompatibility through the MTT assay towards HeLa cells and low hemolytic properties by hemolysis assay, which could be applied for in vivo optical and CT imaging. After intravenous injection of citrate-coated BYT UCNPs for one month, blood biochemistry and histology analysis of mice suggest the UCNPs have a negligible toxicity in vivo, implying citrate-coated BYT could be employed as a safe bioprobe for NIR optical and CT dual-modal imaging.

Improved photon upconversion photoluminescence and intrinsic optical bistability from a rare earth co-doped lanthanum oxide phosphor via Bi3+ doping

An Er³⁺, Yb³⁺, Bi³⁺ co-doped La₂O₃ phosphor shows upconverted emission and intrinsic optical bistability properties.

A cation-exchange controlled core-shell MnS@Bi2S3 theranostic platform for multimodal imaging guided radiation therapy with hyperthermia boost

Overtreatment as a crucial modern medicine issue needs to be urgently addressed. Theranostic agents supply a unique platform and integrate multiple diagnosis and therapies to deal with this issue. In this study, a core-shell MnS@Bi₂S₃ nanostructure was fabricated via two step reactions for tri-modal imaging guided thermo-radio synergistic therapy. The mass ratio between the core and shell of the constructed MnS@Bi₂S₃ can be precisely controlled via cation exchange reaction. After surface PEGylation, MnS@Bi₂S₃-PEG nanoparticles exhibited excellent aqueous medium dispersibility for bioapplications. Based on the r₁ and r₂ relaxivity obtained from the MnS core and the strong near-infrared absorption and X-ray attenuation abilities of the Bi₂S₃ shell, the intratumoral injected MnS@Bi₂S₃-PEG can realize in vivo magnetic resonance, computer tomography, and photoacoustic tumor imaging under a single injection dose. Hyperthermia significantly boosts the efficacy of radiation therapy, showing synergistic tumor treatment efficacy. No obvious toxicity is monitored for the treated mice. Our study not only provides a new way to precisely construct the core-shell nanocomposite, but also presents a unique theranostic platform and unifies the solutions for the challenges related with high injection dose and overtreatment.

Ultrafast Synthesis of Novel Hexagonal Phase NaBiF4 Upconversion Nanoparticles at Room Temperature

Upconversion (UC) nanoparticles (UCNPs) have evoked considerable attention in many fields owing to their fascinating features. However, rigorous synthesis conditions and expensive raw materials often limit their further applications. Here, a novel hexagonal phase NaBiF₄ UC matrix through a very facile method (one min only at room temperature) is synthesized. The nanoparticles show good monodispersity with uniform size. Under the 980 nm irradiation, Yb³⁺ /Ln³⁺ (Ln = Er, Ho, Tm) codoped NaBiF₄ nanoparticles show excellent UC luminescence (UCL). This super facile synthesis strategy and excellent matrix materials enable to achieve UCL in such low temperature, opening a new gateway for the UCNPs applied to a variety of areas in the future.

Surfactant-Free Aqueous Synthesis of Novel Ba2GdF7:Yb3+, Er3+@PEG Upconversion Nanoparticles for in Vivo Trimodality Imaging

In this work, we developed the surfactant-free aqueous synthesis of novel polyethylene glycol (PEG) coated Ba₂GdF₇:Yb³⁺, Er³⁺ upconversion nanoparticles (named as, Ba₂GdF₇:Yb³⁺, Er³⁺@PEG UCNPs) for in vivo multimodality imaging including upconversion luminescence (UCL), X-ray computed tomography (CT), and T₁-weighted magnetic resonance (MR). The as-prepared Ba₂GdF₇:Yb³⁺, Er³⁺@PEG UCNPs not only present bright UCL and reasonably high CT/MR enhancements but also exhibit excellent colloidal stability, inappreciable cytotoxicity, and negligible organ toxicity. In particular, the Ba₂GdF₇:Yb³⁺, Er³⁺@PEG UCNPs emit red UCL with high intensity in the tumor site after intravenous injection via the tail vein of a nude mouse. The Ba₂GdF₇:Yb³⁺, Er³⁺@PEG UCNPs as contrast agents exhibit high-performance for in vivo trimodality (UCL/CT/MR) imaging of a tumor during HepG2 tumor-bearing nude mouse experiments.

Synthetic Glycopolymers for Highly Efficient Differentiation of Embryonic Stem Cells into Neurons: Lipo- or Not?

To realize the potential application of embryonic stem cells (ESCs) for the treatment of neurodegenerative diseases, it is a prerequisite to develop an effective strategy for the neural differentiation of ESCs so as to obtain adequate amount of neurons. Considering the efficacy of glycosaminoglycans (GAG) and their disadvantages (e.g., structure heterogeneity and impurity), GAG-mimicking glycopolymers (designed polymers containing functional units similar to natural GAG) with or without phospholipid groups were synthesized in the present work and their ability to promote neural differentiation of mouse ESCs (mESCs) was investigated. It was found that the lipid-anchored GAG-mimicking glycopolymers (lipo-pSGF) retained on the membrane of mESCs rather than being internalized by cells after 1 h of incubation. Besides, lipo-pSGF showed better activity in promoting neural differentiation. The expression of the neural-specific maker β3-tubulin in lipo-pSGF-treated cells was ∼3.8- and ∼1.9-fold higher compared to natural heparin- and pSGF-treated cells at day 14. The likely mechanism involved in lipo-pSGF-mediated neural differentiation was further investigated by analyzing its effect on fibroblast growth factor 2 (FGF2)-mediated extracellular signal-regulated kinases 1 and 2 (ERK1/2) signaling pathway which is important for neural differentiation of ESCs. Lipo-pSGF was found to efficiently bind FGF2 and enhance the phosphorylation of ERK1/2, thus promoting neural differentiation. These findings demonstrated that engineering of cell surface glycan using our synthetic lipo-glycopolymer is a highly efficient approach for neural differentiation of ESCs and this strategy can be applied for the regulation of other cellular activities mediated by cell membrane receptors.

Optimization of Bi3+ in Upconversion Nanoparticles Induced Simultaneous Enhancement of Near-Infrared Optical and X-ray Computed Tomography Imaging Capability

Bioimaging probes have been extensive studied for many years, while it is still a challenge to further improve the image quality for precise diagnosis in clinical medicine. Here, monodisperse NaGdF₄:Yb³⁺,Tm³⁺,x% Bi³⁺ (abbreviated as GYT-x% Bi³⁺, x = 0, 5, 10, 15, 20, 25, 30) upconversion nanoparticles (UCNPs) have been prepared through the solvothermal method. The near-infrared upconversion emission intensity of GYT-25% Bi³⁺ has been enhanced remarkably than that of NaGdF₄:Yb³⁺,Tm³⁺ (GYT) with a factor of ∼60. Especially, the near-infrared upconversion emission band centered at 802 nm is 150 times stronger than the blue emission band of GYT-25% Bi³⁺ UCNPs. Such high ratio of NIR/blue UCL intensity could reduce the damage to tissues in the bioimaging process. The possibility of using GYT-25% Bi³⁺ UCNPs with strong near-infrared upconversion emission for optical imaging in vitro and in vivo was performed. Encouragingly, the UCL imaging penetration depth can be achieved as deep as 20 mm. Importantly, GYT-25% Bi³⁺ UCNPs exhibit a much higher X-ray computed tomography (CT) contrast efficiency than GYT and iodine-based contrast agent under the same clinical conditions, due to the high X-ray attenuation coefficient of bismuth. Hence, simultaneous remarkable enhancement of NIR emission and X-ray CT signal in upconversion nanoparticles could be achieved by optimizing the doping concentration of Bi³⁺ ions. Additionally, Gd³⁺ ions in the UCNPs endow GYT-25% Bi³⁺ UCNPs with T₁-weighted magnetic resonance (MR) imaging capability.

NIR-driven graphitic-phase carbon nitride nanosheets for efficient bioimaging and photodynamic therapy

Photodynamic therapy (PDT) is a noninvasive and promising anticancer therapy modality that utilizes the photochemical reactions of photosensitizers, upon irradiation at a specific wavelength, to yield reactive oxygen species (ROS) to impair malignant cancer cells.

The progress of single-band upconversion nanomaterials

An overview of the recent progresses in realizing single-band UC emission through different methods and the related mechanisms are given for the first time. The challenges and future perspectives of these novel NMs are stated.