Biological applications of rare-earth based nanoparticles

Trends in targeted delivery of nanomaterials in colon cancer diagnosis and treatment

Colon cancer is an adenocarcinoma, which subsequently develops into malignant tumors, if not treated properly. The current colon cancer therapy mainly revolves around chemotherapy, radiotherapy and surgery, but the search continues for more effective interventions. With the advancement of nanoparticles (NPs), it is now possible to diagnose and treat colon cancers with different types, shapes, and sizes of NPs. Nanoformulations such as quantum dots, iron oxide, polymeric NPs, dendrimers, polypeptides, gold NPs, silver NPs, platinum NPs, and cerium oxide have been either extensively used alone or in combination with other nanomaterials or drugs in colon cancer diagnosis, and treatments. These nanoformulations possess high biocompatibility and bioavailability, which makes them the most suitable candidates for cancer treatment. The size and shape of NPs are critical to achieving an effective drug delivery in cancer treatment and diagnosis. Most NPs currently are under different testing phases (in vitro, preclinical, and clinical), whereas some of them have been approved for therapeutic applications. We have comprehensively reviewed the recent advances in the applications of NPs-based formulations in colon cancer diagnosis and treatment.

Synthesis of water-soluble europium-containing nanoprobes via polymerization-induced self-assembly and their cellular imaging applications

Lanthanide nanoprobes have attracted extensive attention for applications in cellular imaging and biological sensing. Herein, water-dispersible europium (III)-based (Eu(III)-based) nanoprobes were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA) of hydrophobic monomers (Eu(III)-containing monomer and methyl methacrylate (MMA)) using hydrophilic macro-chain transfer agent poly(PEGMA)-CTA. The resulted poly(PMEu) nanoprobes showed spherical in shape in good monodispersity with average diameters of around 210 nm. The poly(PMEu) nanoprobles excellent aqueous dispersity, high aqueous stability and good luminescence properties with quantum yields of 37.21% and fluorescence lifetime of 312.4 μs. Moreover, the poly(PMEu) nanoprobes exhibited good cellular biocompatibility with cell viabilities of 88.2% and high fluorescence intensity for in vitro cellular imaging. The present approach provides a facile strategy for fabrication of luminescent Eu(III)-based nanoprobes with great potential applications for biological imaging.

Age-Related Effects of Orthovanadate Nanoparticles Involve Activation of GSH-Dependent Antioxidant System in Liver Mitochondria

Vanadium is an important ultra-trace element nowadays attracting attention with particular emphasis on medical application. But the therapeutic application of vanadium-based drugs is still questionable and restricted due to some toxic side effects. It was found that unique redox properties of vanadium in nanoform provided antioxidant activity and prevented oxidative disturbance in cells in vitro. Though, on the organism level, ambiguous effects of vanadium-based nanoparticles were observed. In this study, the age-related features of prooxidant/antioxidant balance in blood serum and liver mitochondrial and postmitochondrial fractions of 3 and 18-month-old Wistar male rats treated with orthovanadate nanoparticles (GdVO₄/Eu³⁺, 8 × 25 nm) within 2 months have been investigated. Prooxidant potential-related indexes were the content of lipid hydroperoxides as well as aconitase activity. Activity of glutathione peroxidase, glutathione-S-transferase, glutaredoxin, glutathione reductase, glucose-6-phosphate dehydrogenase, and NADPH-dependent isocitrate dehydrogenase designated the tissue antioxidant potential. Based on the obtained values, the integral index of the prooxidant/antioxidant balance-the reliability coefficient (Kr) has been calculated. The data show that due to activation some chain links of GSH-dependent antioxidant system, GdVO₄/Eu³⁺ nanoparticles increase the reliability of the prooxidant-antioxidant balance in tissues and especially in the liver mitochondria of old animals (Kr in mitochondria of young rats was 2.94, and in mitochondria of old ones-9.83 conventional units). Detected in vitro glutathione peroxidase-like activity of the GdVO₄/Eu³⁺ nanoparticles is supposed to be among factors increasing the reliability of the system. So, for the first time, the beneficial effect of the long-term orthovanadate nanoparticle consumption in old males has been discovered.

Upconversion Nanoparticles Encapsulated with Amorphous Silica and Their Emission Quenching by FRET: A Nanosensor Excited by NIR for Mercury Detection

Near-infrared (NIR) region has been considered as a diagnostic window since it avoids sample autofluorescence and light scattering. Upconversion nanoparticles (UCNPs) convert NIR light into high energy excitation light, making them a suitable excitation source for nanoprobes with deep penetration depth and high signal-to-noise ratio. The current work reported a rhodamine-derived probe for the detection of Hg(II). Corresponding absorption and emission responses for Hg(II) and detailed recognizing mechanism were discussed. An absorption titration experiment was performed. It was found that Hg(II) directly bonded with probe with chemical stoichiometry of 1:1, its association constant was calculated as 2.59 × 105 M−1. Such a high value indicated a direct coordination affinity between Hg(II) and this rhodamine-derived probe. Most metal cations exerted no increasing effect on the probe emission or absorption, exhibiting good sensing selectivity of probe towards Hg(II). Upconversion nanoparticles (UCNPs) were firstly encapsulated with silica (SiO2) and then bonded with the probe via a covalent bond. Given a near-infrared (NIR) laser excitation with wavelength of 980 nm, this probe, (E)-2-((3′,6′-bis(diethylamino)-2′,7′-dimethyl-3-oxospiro[isoindoline-1,9′-xanthen]-2-yl)imino)acetaldehyde (denoted as RHO), captured the energy of UCNPs via a FRET (fluorescence resonance energy transfer) path, resulting in the emission quenching of UCNPs. This composite system showed linear sensing behavior towards Hg(II) with high selectivity, which was similar to the case of pure probe. No probe emission, however, was observed from the composite system, which was different from the case of most literature reports. The self-quenching between probe molecules was claimed responsible for the probe emission, which was confirmed by experiment result and analysis. To the best of our knowledge, this is the first demonstration of covalently integrating SiO2-coated UCNPs with a rhodamine-derived probe for Hg(II) sensing.

Development of Non-Porous Silica Nanoparticles towards Cancer Photo-Theranostics

Nanoparticles have demonstrated several advantages for biomedical applications, including for the development of multifunctional agents as innovative medicine. Silica nanoparticles hold a special position among the various types of functional nanoparticles, due to their unique structural and functional properties. The recent development of silica nanoparticles has led to a new trend in light-based nanomedicines. The application of light provides many advantages for in vivo imaging and therapy of certain diseases, including cancer. Mesoporous and non-porous silica nanoparticles have high potential for light-based nanomedicine. Each silica nanoparticle has a unique structure, which incorporates various functions to utilize optical properties. Such advantages enable silica nanoparticles to perform powerful and advanced optical imaging, from the in vivo level to the nano and micro levels, using not only visible light but also near-infrared light. Furthermore, applications such as photodynamic therapy, in which a lesion site is specifically irradiated with light to treat it, have also been advancing. Silica nanoparticles have shown the potential to play important roles in the integration of light-based diagnostics and therapeutics, termed "photo-theranostics". Here, we review the recent development and progress of non-porous silica nanoparticles toward cancer "photo-theranostics".

KLa(0.95-x)GdxF4:Eu3+ hexagonal phase nanoparticles as luminescent probes for in vitro Huh-7 cancer cell imaging

A facile chemical route is reported for synthesizing red-emitting photoluminescent/MRI multi-functional KLa(0.95-x)GdxF4:Eu3+ (x = 0 to 0.4) bio-compatible nanomaterials for targeted in vitro tumor imaging. Hexagonal phase pure nanoparticles show a significant and systematic change in morphology with enhanced photoluminescence due to the substitution of La3+ with Gd3+ ions. Single phase β-KLa(0.95-x)GdxF4:Eu3+ exhibits multifunctional properties, both intense red emission and strong paramagnetism for high-contrast bioimaging applications. These silica capped magnetic/luminescent nanoparticles show long-term colloidal stability, optical transparency in water, strong red emission, and low cytotoxicity. The cellular uptake of coated nanoparticles was investigated in liver cancer cell line Huh-7. Our findings suggest that these nanoparticles can serve as highly luminescent imaging probes for in vitro applications with potential for in vivo and live cell imaging applications.

The nano-bio interactions of rare-earth doped BaF2 nanophosphors shape the developmental processes of zebrafish

Nanoparticles with biomedical applications should be evaluated for their biocompatibility. Rare-earth doped nanoparticles with unique spectral properties are superior in vivo optical probes in comparison with quantum dots and organic dyes, however, studies describing their nano-bio interactions are still limited. Here, we have evaluated the nano-bio interactions of green-synthesized, phase-pure BaF₂ nanoparticles doped with rare-earth (RE³⁺ = Ce³⁺/Tb³⁺) ions using larval zebrafish. We found that zebrafish can tolerate a wide concentration range of these nanoparticles, as the maximal lethality was observed at very high concentrations (more than 200 mg L^-1) upon five days of continuous exposure. At a concentration of 10 mg L^-1, at which Zn²⁺, Ti⁴⁺ and Ag⁺ nanoparticles are reported to be lethal to developing zebrafish, continuous exposure to our nanoparticles for four days produced no developmental anomalies, craniofacial defects, cardiac toxicity or behavioural abnormalities in the developing zebrafish larvae. We have also found that the doping of rare-earth ions has no major effect on these biomarkers. Interestingly, the function of acetylcholinesterase (AChE) and the cellular metabolic activity of whole zebrafish larvae remained unchanged, even during continuous exposure to these nanoparticles at 150 mg L^-1 for four days; however, severe developmental toxicities were evident at this high concentration. Based on these results, we can conclude that the biocompatibility of rare-earth doped nanoparticles is concentration dependent. Not all biomarkers are sensitive to these nanoparticles. The high concentration-dependent toxicity occurs through a mechanism distinct from changes in the metabolic or AChE activity. The significance of these findings lies in using these nanoparticles for bioimaging applications and biomarker studies, especially for prolonged exposure times.

Separation of Radioactive Elements from Rare Earth Element-Bearing Minerals

Rare earth elements (REE), originally found in various low-grade deposits in the form of different minerals, are associated with gangues that have similar physicochemical properties. However, the production of REE is attractive due to their numerous applications in advanced materials and new technologies. The presence of the radioactive elements, thorium and uranium, in the REE deposits, is a production challenge. Their separation is crucial to gaining a product with minimum radioactivity in the downstream processes, and to mitigate the environmental and safety issues. In the present study, different techniques for separation of the radioactive elements from REE are reviewed, including leaching, precipitation, solvent extraction, and ion chromatography. In addition, the waste management of the separated radioactive elements is discussed with a particular conclusion that such a waste stream can be employed as a valuable co-product.

Selective Sensing of Cu2+ and Fe3+ Ions with Vis-Excitation using Fluorescent Eu3+-Induced Aggregates of Polysaccharides (EIAP) in Mammalian Cells and Aqueous Systems

Fluorescent lanthanide complexes have favorable features for fluorescence-based sensors compared to organic fluorophores and quantum dots. They exhibit very long fluorescence lifetimes, sharp emission bands, and stability with respect to photo-bleaching, without blinking. However, these complexes are usually hydrophobic, and many are excited by UV light, making them hazardous and incompatible with aqueous environments and biological samples. In this work, the strong fluorescent Eu³⁺-induced aggregates of polysaccharides (EIAP) was used to improve their aqueous solubility, and to tune the appropriate excitation wavelength in the visible range for avoiding toxicity of UV light in biological applications. The complexes exhibit bright fluorescence with an excitation maximum in the visible range, near 405 nm. EIAP 3 also exhibit rapid quenching response in the presence of transition metal ions. This enables the detection of Cu²⁺ and Fe³⁺ below 1 ppm. The reverse of quenching response of copper by the addition of a chelating agent makes it possible to recover the fluorescence property. Successfully, the EIAP exhibit cytocompatibility with mammalian cells. Thus, these new polysaccharide-based complexes have the potential for rapid, sensitive and selective metal ion sensors for the environmental systems.

The near-infrared autofluorescence fingerprint of the brain

The brain is a vital organ involved in most of the central nervous system disorders. Their diagnosis and treatment require fast, cost-effective, high-resolution and high-sensitivity imaging. The combination of a new generation of luminescent nanoparticles and imaging systems working in the second biological window (near-infrared II [NIR-II]) is emerging as a reliable alternative. For NIR-II imaging to become a robust technique at the preclinical level, full knowledge of the NIR-II brain autofluorescence, responsible for the loss of image resolution and contrast, is required. This work demonstrates that the brain shows a peculiar infrared autofluorescence spectrum that can be correlated with specific molecular components. The existence of particular structures within the brain with well-defined NIR autofluorescence fingerprints is also evidenced, opening the door to in vivo anatomical imaging. Finally, we propose a rational selection of NIR luminescent probes suitable for low-noise brain imaging based on their spectral overlap with brain autofluorescence.

Single-Nanocrystal Studies on the Homogeneity of the Optical Properties of NaYF4:Yb3+,Er3

Development of upconverting nanomaterials which are able to emit visible light upon near-infrared excitation opens a wide range of potential applications. Because of their remarkable photostability, they are widely used in bioimaging, optogenetics, and optoelectronics. In this work, we demonstrate the influence of several experimental conditions as well as a dopant concentration on the luminescence properties of upconverting nanocrystals (UPNCs) that need to be taken into account for their efficient use in the practical applications. We found that not only nanoparticle architecture affects the optical properties of UPNCs, but also factors such as sample concentration, excitation light power density, and temperature may influence the green-to-red emission ratio. We performed studies on both the single-nanoparticle and ensemble levels over a broad concentration range and found the heterogeneity in the optical properties of UPNCs with low dopant concentrations.

Red emitting CaTiO3: Pr3+ nanophosphors for rapid identification of high contrast latent fingerprints

Red emitting (~612 nm) CaTiO₃:Pr³⁺ long afterglow nanocrystals with a persistence time ~20 min (dark adapted human eyes) have been synthesised for developing high contrast latent fingerprints using the sol-gel process. Due to the persistent emission, CaTiO₃:Pr³⁺ nanophosphor does not require a continuous source for excitation, thereby eliminating the background information even from multi-colour substrates, resulting in a high signal to noise ratio. As a consequence of which, minute features of level- I, II and III can be clearly studied in high contrast fingerprints. Considerable blue shift (~20 nm) was recorded in photoluminescence excitation due to the quantum confinement properties of CaTiO₃:Pr³⁺ nanocrystals. Powder x-ray diffraction confirms the formation of a single phase orthorhombic structure of CaTiO₃:Pr³⁺ with average crystallite size ~40 nm. Spectral parameters indicate a very high color purity of 99% with CIE coordinates (0.62, 0.37) which are very close to NTSC standards for an ideal red-emission. Transmission electron microscopy studies confirm the formation of spherical particles with narrow size distribution which makes them suitable to combine with fingerprint development methods such as powder dusting and cyanoacrylate fuming methods.

Bioaccumulation of ytterbium oxide nanoparticles insinuate oxidative stress, inflammatory, and pathological lesions in ICR mice

With the rapid development in nanoscience and nanotechnology, rare earth oxide nanomaterials (REO-NMs) have been increasingly used due to their unique physical and chemical characteristics. Despite the increasing applications of REO NPs, scarce information is available on their detrimental effects. In the current study, we investigate the toxic effect of ytterbium oxide nanoparticles (Yb₂O₃ NPs) in mouse model by using various techniques including inductively coupled plasma mass spectrometry (ICP-MS) analysis over 30 days of exposure. Furthermore, we elucidated lung lavage fluid of mice for biochemical and cytological analysis, and lung tissues for histopathology to interpret the NP side effects. We observed a significant concentration of Yb₂O₃ NPs accumulated in the lung, liver, kidney, and heart tissues. Similarly, increased bioaccumulation of Yb content was found in the olfactory bulb compared to other reigns of brain. The cytological analysis of bronchoalveolar lavage fluid (BALF) revealed a significant elevation in the percentage of neutrophils and lymphocytes. Biochemical analysis showed an instilled Yb₂O₃ NPs, showing signs of oxidative damage through up-regulation of 60-87% of MDA while down-regulation of 20-40% of GSH-PX and GSH content. The toxicity pattern was more evident from histopathological observations. These interpretations provide enough evidence of bioaccumulation of Yb₂O₃ NPs in mice tissues. Overall, our findings reveal that acute exposure of Yb₂O₃ NPs through intranasal inhalation may cause toxicity via oxidative stress, which leads to a chronic inflammatory response. Graphical abstract Graphical illustrations of experimental findings.

A Comparative Study on Luminescence Properties of Y2O3: Pr3+ Nanocrystals Prepared by Different Synthesis Methods

Pr³⁺-doped Y₂O₃ nanocrystals (NCs) have been obtained via five wet-chemistry synthesis methods which were optimized in order to achieve superior optical properties. To this end, a systematic study on the influence of different reaction parameters was performed for each procedure. Specifically, precursor concentration, reaction temperature, calcination temperature, and time, among others, were analyzed. The synthesized Y₂O₃: Pr³⁺ NCs were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and reflectance and Raman spectroscopy. In addition, the optical properties of such NCs were investigated by excitation, emission, and luminescence decay measurements. Concretely, emission from the ¹D₂ level was detected in all samples, while emission from ³P_J was absent. Finally, the effect of the synthesis methods and the reaction conditions on the luminescence decay has been discussed, and a comparative study of the different methods using the fluorescence lifetime of so-obtained Y₂O₃: Pr³⁺ NCs as a figure of merit has been carried out.

Toward a Chemical Control of Colloidal YVO4 Nanoparticles Microstructure

Rare-earth-doped oxides are a class of compounds that have been largely studied in the context of the development of luminescent nanocrystals for various applications including fluorescent labels for bioimaging, MRI contrast agents, luminescent nanocomposite coatings, etc. Elaboration of colloidal suspensions is usually achieved through coprecipitation. Particles exhibit emission properties that are similar to the bulk counterparts, although altered by crystalline defects or surface quenching species. Focusing on YVO₄:Eu, one of the first reported systems, the aim of this work is to revisit the elaboration of nanoparticles obtained through a simple aqueous coprecipitation route. The objective is more precisely to get a better understanding of the parameters affecting the particles' internal microstructure, a feature that is poorly controlled and characterized. We show that the hydroxyl concentration in the precursor solution has a drastic effect on the particles' microstructure. Moreover, discrepancies in the reported particle structure are shown to possibly arise from the carbonation of the strongly basic orthovanadate precursor. For this study, SAXS/WAXS is shown to be a powerful tool to characterize the multiscale structure of the particles. It could be shown that playing on the precursor composition, it may be varied between almost monocrystalline nanocrystals to particles exhibiting a hierarchical microstructure well described by a surface fractal model. This work provides a new methodology for the characterization of nanoparticles microstructure and opens new directions for its optimization in view of applications.

Effect of Cationic Brush-Type Copolymers on the Colloidal Stability of GdPO4 Particles with Different Morphologies in Biological Aqueous Media

In this study, we present the synthesis of cationic brush-type polyelectrolytes and their use in the stabilization of GdPO4 particles in aqueous media. Polymers of various compositions were synthesized via the RAFT polymerization route. SEC equipped with triple detection (RI, DP, RALS, and LALS) was used to determine the molecular parameters (Mn, Mw, Mw/Mn). The exact composition of synthesized polymers was determined using NMR spectroscopy. Cationic brush-type polymers were used to improve the stability of aqueous GdPO4 particle dispersions. First, the IEPs of GdPO4 particles with different morphologies (nanorods, hexagonal nanoprisms, and submicrospheres) were determined by measuring the zeta potential of bare particle dispersions at various pH values. Afterward, cationic brush-type polyelectrolytes with different compositions were used for the surface modification of GdPO4 particles (negatively charged in alkaline media under a pH value of ∼10.6). The concentration and composition effects of used polymers on the change in particle surface potential and stability (DLS measurements) in dispersions were investigated and presented in this work. The most remarkable result of this study is redispersible GdPO4 nanoparticle colloids with increased biocompatibility and stability as well as new insights into possible cationic brush-type polyelectrolyte applicability in both scientific and commercial fields.

Investigating the Size and Microstrain Influence in the Magnetic Order/Disorder State of GdCu2 Nanoparticles

A series of GdCu 2 nanoparticles with controlled sizes ranging from 7 nm to 40 nm has been produced via high-energy inert-gas ball milling. Rietveld refinements on the X-ray diffraction measurements ensure that the bulk crystalline I m m a structure is retained within the nanoparticles, thanks to the employed low milling times ranging from t = 0.5 to t = 5 h. The analysis of the magnetic measurements shows a crossover from Superantiferromagnetism (SAF) to a Super Spin Glass state as the size decreases at NP size of 〈 D 〉 ≈ 18 nm. The microstrain contribution, which is always kept below 1%, together with the increasing surface-to-core ratio of the magnetic moments, trigger the magnetic disorder. Additionally, an extra contribution to the magnetic disorder is revealed within the SAF state, as the oscillating RKKY indirect exchange achieves to couple with the aforementioned contribution that emerges from the size reduction. The combination of both sources of disorder leads to a maximised frustration for 〈 D 〉 ≈ 25 nm sized NPs.

Fabrication of a multifunctional magnetic-fluorescent material for medical applications

Multifunctional biocompatible materials have evoked considerable interest in the field of medical applications. Here we report the thermal decomposition preparation of homogeneous fluorescent-magnetic particles with a composite structure containing CoFe2O4 nanoparticles as nucleation seeds for fluorescent Gd2-xO3:Eux. The composite exhibited a wide range of fluorescence transitions in the whole visible spectrum, displaying 18 different emission peaks when excited at a 250 nm wavelength. Moreover, at low temperature the peaks of the composite were wider than the peaks of the fluorescent material, which may be attributed to a set of new energy levels due to a combination of Stark splitting with the magnetic field of CoFe2O4. Because this material is intended to be used for biomedical applications, the potential toxicity of the composite was tested using an invertebrate hemocyte cell model. The cells showed slight morphological and biochemical changes upon exposure to the composite; however, there was no increase in cell death at concentrations of up to 40 ppm. In addition, the material could be tracked by its fluorescence inside the cells, when excited at a more bio-friendly and less energetic wavelength of 405 nm. Furthermore, MRI showed T1 and T2 dual contrast with relaxivity values in the range of most reported materials.

Luminescent gold nanoclusters for bioimaging applications

Luminescent nanomaterials have emerged as attractive candidates for sensing, catalysis and bioimaging applications in recent years. For practical use in bioimaging, nanomaterials with high photoluminescence, quantum yield, photostability and large Stokes shifts are needed. While offering high photoluminescence and quantum yield, semiconductor quantum dots suffer from toxicity and are susceptible to oxidation. In this context, atomically precise gold nanoclusters protected by thiol monolayers have emerged as a new class of luminescent nanomaterials. Low toxicity, bioavailability, photostability as well as tunable size, composition, and optoelectronic properties make them suitable for bioimaging and biosensing applications. In this review, an overview of the sensing of pathogens, and of in vitro and in vivo bioimaging using luminescent gold nanoclusters along with the limitations with selected examples are discussed.

Accurate detection of β-hCG in women's serum and cervical secretions for predicting early pregnancy viability based on time-resolved luminescent lanthanide nanoprobes

Sensitive and specific detection of β-hCG in women's serum and cervical secretions is of great significance for early pregnancy evaluation. However, the accurate detection of trace amounts of β-hCG in cervical secretions remains challenging because of its low level. Herein, we report a unique strategy for β-hCG detection in a heterogeneous sandwich-type bioassay by using LiLuF₄:Ce,Tb nanoparticles as time-resolved photoluminescence (PL) nanoprobes. By taking advantage of the intense and long-lived PL of the nanoprobes, the short-lived background autofluorescence can be completely eliminated, which enables the sensitive detection of β-hCG with a linear range of 0-10 ng mL^-1 and a detection limit down to 6.1 pg mL^-1, approximately two orders of magnitude improvement relative to that of a commercial β-hCG assay kit. Furthermore, we demonstrate the application of the nanoprobes for accurate detection of β-hCG in clinical serum and cervical secretion samples and unveil that the ratio of β-hCG levels in cervical secretions and serum can be a good indicator of early pregnancy viability in unknown locations. These findings bring new opportunities in perinatal medicine by employing luminescent lanthanide nanoprobes, thus laying a foundation for future development of luminescent nanoprobes for versatile biomedical applications.

Hydrothermal synthesis and site symmetry tuning of polycrystalline YVO4:Eu nanoparticles via a continuous-flow microreactor

Yttrium orthovanadate (YVO₄) has been widely used as a host material for low- and medium-power diode-pumped solid-state lasers due to its excellent thermal, mechanical, and optical properties. This work demonstrates the synthesis and site symmetry tunning of polycrystalline YVO₄:Eu nanoparticles with uniform size and shape using a continuous-flow microreactor at high pressures. High-quality YVO₄:Eu nanoparticles were created using a residence time of fewer than 20 s. Carefully controlling the heat flux and flow rate can produce the YVO₄:Eu nanoparticles showing different crystallinity, crystal morphologies, site symmetry around Eu³⁺, and therefore optical emission. The site symmetry of YVO₄:Eu is adjusted without any stoichiometric modification of the precursors by simply varying the flow rate and heat flux of the microreactor. The site symmetries of the as-synthesized YVO₄:Eu nanoparticles are studied by investigating their photoluminescent emission spectra and computational model of first-principle density functional theory (DFT). The DFT model indicates that the oxygen vacancy influenced the V-O association and the overlap between Eu 4f and V 3d states which can contribute to different optical transitions and, therefore, distinct emission spectrum. The use of a continuous flow microreactor at high pressure provides better understandings of the hydrothermal syntheses of functional nanoparticles and enables scalable manufacturing concurrently.

Nanotoxicological study of downconversion Y2 O3 :Eu3+ luminescent nanoparticles functionalized with folic acid for cancer cells bioimaging

Luminescent lanthanide downconversion nanoparticles (DCNPs) provide a combination of high luminescence intensity, sharp emission peaks with narrow bandwidth and a large Stokes' shift, leading to high-performance biomedical applications mainly for imaging. The purpose of this study is to present a nanotoxicological study of DCNPs Y₂ O₃ codoped with Eu³⁺ and functionalized with folic acid (FA). These assessments include cytotoxicity, genotoxicity, hemocompatibility, and in vitro inflammatory studies. We demonstrated by flow cytometry and confocal microscope the internalization of FA-DCNPs in breast cancer and melanoma cells. They were synthesized by sol-gel method and coated with a thin silica shell to make them biocompatible; also they were functionalized with amino groups and FA ligands that bind to the folate receptors (FR) located on the surface of the cancer cells studied. This functionalization enables the DCNPs to be internalized into the cancer cells via endocytosis by the conjugation FA-FR. The DCNPs were characterized with transmission electron microscope, Fourier transform infrared spectroscopy and photoluminescence. The nanotoxicological assessments demonstrated that both nanoparticles (bare and functionalized) are no cytotoxic and no genotoxic at the tested concentrations (0.01-20 μg/mL) in three cell lines (breast, skin cancer, and osteoblasts). Also they are hemocompatible and do not exert nitric oxide production in vitro by macrophages. The FA-DCNPs were clearly localized into the cell cytoplasm with bright red luminescence. Thus, herein we present a complete nanotoxicological study of FA-DCNPs Y₂ O₃ codoped with Eu³⁺ and we conclude that these nanoparticles are biocompatible and can be further used for cancer cells bioimaging.

Near-IR emissive rare-earth nanoparticles for guided surgery

Intraoperative image-guided surgery (IGS) has attracted extensive research interests in determination of tumor margins from surrounding normal tissues. Introduction of near infrared (NIR) fluorophores into IGS could significantly improve the in vivo imaging quality thus benefit IGS. Among the reported NIR fluorophores, rare-earth nanoparticles exhibit unparalleled advantages in disease theranostics by taking advantages such as large Stokes shift, sharp emission spectra, and high chemical/photochemical stability. The recent advances in elements doping and morphologies controlling endow the rare-earth nanoparticles with intriguing optical properties, including emission span to NIR-II region and long life-time photoluminescence. Particularly, NIR emissive rare earth nanoparticles hold advantages in reduction of light scattering, photon absorption and autofluorescence, largely improve the performance of nanoparticles in biological and pre-clinical applications. In this review, we systematically compared the benefits of RE nanoparticles with other NIR probes, and summarized the recent advances of NIR emissive RE nanoparticles in bioimaging, photodynamic therapy, drug delivery and NIR fluorescent IGS. The future challenges and promises of NIR emissive RE nanoparticles for IGS were also discussed.

Oxidative cyclization of thiosemicarbazide: a chemodosimetric approach for the highly selective fluorescence detection of cerium(iv)

A simple thiosemicarbazide-based chemodosimeter was employed to detect Ce⁴⁺ ion through turn-on fluorescence.

Cerium oxide nanoparticles: properties, biosynthesis and biomedical application

Cerium oxide nanoparticles have revolutionized the biomedical field and is still in very fast pace of development. Hence, this work elaborates the physicochemical properties, biosynthesis, and biomedical applications of cerium oxide nanoparticles.

Photon management properties of Yb-doped SnO2 nanoparticles synthesized by the sol-gel technique

SnO2 is a transparent large band gap semiconductor, particularly interesting for optoelectronic and photovoltaic devices, mainly because its conduction can be easily tuned by doping or by modulating the amount of oxygen vacancies. Besides, rare earth doping was successfully exploited for up conversion properties. Here we report on the functionalization of SnO2 nanoparticles with optically active Yb3+ ions using the sol-gel method, which allows UV to NIR spectral (down) conversion. As starting solutions we used stable non-alkoxide metal-organic compounds, which is rather uncommon. Transmission electron microscopy analysis demonstrated the formation of small well-crystallized nanoparticles while X-ray photoelectron spectroscopy measurements have revealed that the Yb is well inserted in the host matrix and has a 3+ valence state. All nanoparticles present large absorption in the UV-visible range (250 to 550 nm) and a band gap that decreases down to 2.72 eV upon doping. The UV energy converted into NIR on the basis of efficient energy transfer from SnO2 to the Yb3+ ions ranges between 250 and 400 nm. Reference undoped SnO2 nanoparticles with a mean size of 20 nm allow converting UV light into broad visible emission centered at 650 nm. The incorporation of up to 3.5 at% of Yb3+ ions into the SnO2 host matrix results in a spectacular decrease of the nanoparticle size down to 6.6 nm. This allowed also the shift of the photoluminescence to NIR in the 970-1050 nm range. The energy level structure of Yb3+ in SnO2 was successfully determined from the deconvolution of the Yb emission. This emission is significantly enhanced by increasing the doping level. All optical measurements suggest that these nanoparticles can be efficiently used as down-shifting converters.

Tumor Targeting Strategies of Smart Fluorescent Nanoparticles and Their Applications in Cancer Diagnosis and Treatment

Advantages such as strong signal strength, resistance to photobleaching, tunable fluorescence emissions, high sensitivity, and biocompatibility are the driving forces for the application of fluorescent nanoparticles (FNPs) in cancer diagnosis and therapy. In addition, the large surface area and easy modification of FNPs provide a platform for the design of multifunctional nanoparticles (MFNPs) for tumor targeting, diagnosis, and treatment. In order to obtain better targeting and therapeutic effects, it is necessary to understand the properties and targeting mechanisms of FNPs, which are the foundation and play a key role in the targeting design of nanoparticles (NPs). Widely accepted and applied targeting mechanisms such as enhanced permeability and retention (EPR) effect, active targeting, and tumor microenvironment (TME) targeting are summarized here. Additionally, a freshly discovered targeting mechanism is introduced, termed cell membrane permeability targeting (CMPT), which improves the tumor-targeting rate from less than 5% of the EPR effect to more than 50%. A new design strategy is also summarized, which is promising for future clinical targeting NPs/nanomedicines design. The targeting mechanism and design strategy will inspire new insights and thoughts on targeting design and will speed up precision medicine and contribute to cancer therapy and early diagnosis.

GdVO4:Eu3+,Bi3+ Nanoparticles as a Contrast Agent for MRI and Luminescence Bioimaging

With the development of multifunctional imaging, gadolinium (Gd)-bearing inorganic nanoparticles (NPs), which were doped with trivalent lanthanide (Ln3+), have been applied in magnetic resonance imaging (MRI) and optical imaging owing to their high payload of Gd3+ ions and specific optical characteristics. In this study, we chose GdVO4 codoped with Eu3+ and Bi3+ as the host material to generate a highly efficient contrast agent (CA) for MRI and long-term luminescence imaging. The new CA emits strong and stable luminescence because of its strong characteristic emissions, resulting from the energy-transfer process from the vanadate groups (VO4 3-) to the Eu3+ and Bi3+ dopants. Additionally, these NPs provided conspicuous T 1 and T 2 relaxation time-shortening characteristics, which result in MRI enhancement. GdVO4:Eu3+,Bi3+ NPs were tested on liver tumor-bearing nude mice, and showed improved liver tumor contrast in T 2-weighted MR images (T 2WI). The dual-modal imaging probe exhibited no cytotoxicity or organ toxicity, reflecting its excellent biocompatibility. Thus, GdVO4:Eu3+,Bi3+ has the potential to be used for bioassays in vitro and liver tumor targeting in vivo. The results reveal the great promise of using the designed GdVO4:Eu3+,Bi3+ NPs as luminescent and MRI dual-mode bioprobes for clinical bioimaging applications.

Radionuclide-Activated Nanomaterials and Their Biomedical Applications

Radio-nanomedicine, or the use of radiolabeled nanoparticles in nuclear medicine, has attracted much attention in the last few decades. Since the discovery of Cerenkov radiation and its employment in Cerenkov luminescence imaging, the combination of nanomaterials and Cerenkov radiation emitters has been revolutionizing the way nanomaterials are perceived in the field: from simple inert carriers of radioactivity to activatable nanomaterials for both diagnostic and therapeutic applications. Herein, we provide a comprehensive review on the types of nanomaterials that have been used to interact with Cerenkov radiation and the gamma and beta scintillation of radionuclides, as well as on their biological applications.

Effects of structural distinction in neodymium nanoparticle for therapeutic application in aberrant angiogenesis

In the present study we analyzed the effect of structural distinction in neodymium nanostructures for modulating angiogenic process as the strategy for identifying biocompatible Nano therapeutics for biomedical applications. We observed structural dependence of Nd nanoparticles on biocompatibility, the spherical polymorphs showed better biocompatibility when compared with cuboidal and nanorod shaped polymorphs of neodymium. The Nd nanopolymorphs in spherical morphology exhibited least redox modulating effect compared to cuboidal shaped that was higher when compared to Nd nanorods. The efficacy of the Nd Nanopolymorphs to induce biological effect in particular on angiogenic process was observed to be directly related to the polymorphs ability to modulate redox signaling. The redox signaling was observed to be via PKM2-NOX4 signaling pathways. Further the results demonstrated that ROS generated by cuboid and rod shaped nanopolymorphs activated the pro-angiogenic factors namely VE-cadherin, HIF 1α, VEGF and VEGFR-2 to facilitate the angiogenic process. The manuscript highlights the importance of rare earth metal nanoparticles in modulating biological process for therapeutic interventions. The present study opens up a new domain in developing novel biocompatible therapeutics based on rare earth metal nanoparticles for regulating disease pathophysiology.

Enhancement of Eu3+ Emission in YVO4:Eu3+ Nanocrystals by Li+ Codoping: An Oxidant-Resistant Dispersion and Polymer Film

The enhancement of red emission of YVO₄:Eu³⁺ nanocrystals by Li⁺ codoping has been achieved. The effect of Li⁺ codoping on the crystalline properties and the luminescence of Eu³⁺ has been thoroughly studied. An increase of the unit cell volume and crystallinity of the nanocrystals is observed as the concentration of Li⁺ codoping increases. The lattice expansion could be related to occupation of the interstitial sites by the Li⁺ ions. The nanocrystals appear to be assemblies of rodlike nanostructures along with cube-shaped rough nanostructures of uniform size. The optimum concentration of Li⁺ codoping for luminescence enhancement is found to be 5 at. % at which Eu³⁺ emission is increased by about 2.5 times. The fall in Eu³⁺ emission after codoping of Li⁺ (7-15 at. %) is observed. Is it the increased crystallinity (i.e., the size) or the lattice expansion that poses a limit to luminescence enhancement? Annealing at 500 and 850 °C increased the luminescence emission by threefold and fivefold, respectively. The samples are readily dispersible in deionized water and incorporated easily in the flexible polymer film made of polyvinylidene fluoride. The dispersion-in-water shows bright red luminescence as low as 50 μg/mL. The emission intensity of the dispersion decreases linearly with concentration with a slope almost equal to unity. The dispersion and the flexible film do not show luminescence degradation under the influence of oxidizing H₂O₂ medium. The oxidant-resistant nature with enhanced luminescence could serve as a suitable red emitter for lighting and display applications.

Facile synthesis of cerium-doped carbon quantum dots as a highly efficient antioxidant for free radical scavenging

Excessive reactive oxygen species (ROS) can lead to irreversible damage to the human body in vivo, therefore it is highly desirable to exploit an efficient antioxidant. Recently, cerium oxide nanoparticles have attracted extensive attention in the field of biomedicine due to their excellent antioxidant properties. In this study, cerium-doped carbon quantum dots (Ce-doped CQDs) with hydroxyl radical scavenging capacity were synthesized for first time by one-step hydrothermal carbonization method. The resultant Ce-doped CQDs with the average particle size of 2.5 nm possessed the properties of good water solubility, colloid stability, and strong fluorescence, which are similar to traditional CQDs. Meanwhile, the Ce-doped CQDs had good biocompatibility and negligible cytotoxicity. Taking advantage of inherent ultra-small size, the Ce-doped CQDs exhibited a high Ce³⁺/Ce⁴⁺ ratio at the surface of particles. The radical scavenging capability of the Ce-doped CQDs was proved by a simple photometric system in vitro, which provided direct evidence for its antioxidant potency. Furthermore, the Ce-doped CQDs had a high ability to protect cells from hydrogen peroxide-induced damage by scavenging hydroxyl radicals. These results suggest that Ce-doped CQDs as a new ROS scavenger may provide potential prospects for the treatment of oxidative stress-related diseases.

Green Fluorescent Terbium (III) Complex Doped Silica Nanoparticles

The low photostability of conventional organic dyes and the toxicity of cadmium-based luminescent quantum dots have prompted the development of novel probes for in vitro and in vivo labelling. Here, a new fluorescent lanthanide probe based on silica nanoparticles is fabricated and investigated for optically traceable in vitro translocator protein (TSPO) targeting. The targeting and detection of TSPO receptor, overexpressed in several pathological states, including neurodegenerative diseases and cancers, may provide valuable information for the early diagnosis and therapy of human disorders. Green fluorescent terbium(III)-calix[4]arene derivative complexes are encapsulated within silica nanoparticles and surface functionalized amine groups are conjugated with selective TSPO ligands based on a 2-phenylimidazo[1,2-a]pyridine acetamide structure containing derivatizable carboxylic groups. The photophysical properties of the terbium complex, promising for biological labelling, are demonstrated to be successfully conveyed to the realized nanoarchitectures. In addition, the high degree of biocompatibility, assessed by cell viability assay and the selectivity towards TSPO mitochondrial membrane receptors, proven by subcellular fractional studies, highlight targeting potential of this nanostructure for in vitro labelling of mitochondria.

Selective cellular imaging with lanthanide-based upconversion nanoparticles

Upconversion nanoparticles (UCNPs) with sodium yttrium fluoride, NaYF4 (host lattice) doped with Yb3+ (sensitizer) and Er3+ (activator) were synthesized via hydrothermal route incorporating polyethyleneimine (PEI) for their long-term stability in water. The cationic PEI-modified UCNPs with diameter 20 ± 4 nm showed a zeta potential value of +36.5 mV and showed an intense, visible red luminescence and low-intensity green emission with 976 nm laser excitation. The particles proven to be nontoxic to endothelial cells, with a 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay, showing 90% to 100% cell viability, across a wide range of UCNP concentrations (0.3 ng/mL-0.3 mg/mL) were used in multiphoton imaging. Multiphoton cellular imaging and emission spectroscopy data reported here prove that the UCNPs dispersed in cell culture media are predominantly concentrated in the cytoplasm than the cell nucleus. The energy transfer from PEI-coated UCNPs to surrounding media for red luminescence in the biological system is also highlighted with spectroscopic measurements. Results of this study propose that UCNPs can, therefore, be used for cytoplasm selective imaging together with multiphoton dyes (eg, 4',6-diamidino-2-phenylindole (DAPI)) that are selective to cell nucleus.

Preparation and evaluation of fluorescent poly(p-phenyleneethylene) covalently coated microspheres with reactive sites for bioconjugation

Fluorescent microspheres with reactive sites for interacting with biomolecules are greatly demanded in flow cytometry based suspension array. Aiming to develop a new method for preparing fluorescent microspheres, two poly(p-phenyleneethylene) (PPE) conjugated polymers (CPs) with pedant carboxylic groups were synthesized via Sonogashira coupling and followed with hydrolysis of ester groups; then the conjugated polymers were immobilized onto monodispersed amino-modified porous poly(glycidylmethacrylate) (APGMA) microspheres via coupling reaction between carboxylic and amino groups to give APGMA-CP fluorescent microspheres. The fluorescent microspheres were found to have good photo- and thermal stability as well as negligible influence from rigorous washing. The emission was uniform all across the inner and surface of the spheres. To evaluate the effectiveness of bioconjugation on the fluorescent microspheres, fluorescein isothiocyanate isomer I (FITC) labeled bovine serum albumin (BSA) (BSA-FITC) was chosen as the representative biomolecule to react with the fluorescent microspheres to give APGMA-CP-BSA-FITC. In the flow cytometry study, fluorescence compensation between the V500 and FITC detectors (receiving signals from fluorophores excited by 405 nm and 488 nm, respectively), to remove the interference between the emission of FITC and CPs, was realized using singly-stained microspheres. Finally, APGMA-CP-BSA-FITC microspheres were found to be double positive for CP and FITC with very high percentage (>95%), suggesting the bioconjugation is very effective. This study provides a facile method for simultaneous introduction of fluorescence and reactive sites onto the microspheres, which is very promising to be used as general strategy for fabricating fluorescence microspheres for application in high-throughput technology.

Pressure Effects on the 4f Electronic Structure of Light Lanthanides

Using the satellite structure of the Lγ_{1} line in nonresonant x-ray emission spectra, we probe the high-pressure evolution of the bare 4f signature of the early light lanthanides at ambient temperature. For Ce and Pr the satellite peak experiences a sudden reduction concurrent with their respective volume collapse (VC) transitions. These new experimental results are supported by calculations using state-of-the-art extended atomic structure codes for Ce and Pr, and also for Nd, which does not exhibit a VC. Our work suggests that changes to the 4f occupation are more consistently associated with evolution of the satellite than is the reduction of the 4f moment. Indeed, we show that in the case of Ce, mixing of a higher atomic angular momentum state, driven by the increased hybridization, acts to obscure the expected satellite reduction. These measurements emphasize the importance of a unified study of a full set of microscopic observables to obtain the most discerning test of the underlying, fundamental f-electron phenomena at high pressures.

Emerging applications of upconverting nanoparticles in intestinal infection and colorectal cancer

Colorectal cancer is the abnormal growth of cells in colon or rectum. Recent findings have acknowledged the role of bacterial infection and chronic inflammation in colorectal cancer initiation and progression. In order to detect and treat precancerous lesions, new tools are required, which may help to prevent or identify colorectal cancer at an early stage. To date, several different screening tests are available, including endoscopy, stool-based blood tests, and radiology-based tests. However, these analyses either lack sensitivity or are of an invasive nature. The use of fluorescently labeled probes can increase the detection sensitivity. However, autofluorescence, photobleaching, and photodamage are commonly encountered problems with fluorescence imaging. Upconverting nanoparticles (UCNPs) are recently developed lanthanide-doped nanocrystals that can be used as light-triggered luminescent probes and in drug delivery systems. In this review, we comprehensively summarize the recent developments and address future prospects of UCNP-based applications for diagnostics and therapeutic approaches associated with intestinal infection and colorectal cancer.