Inorganic phosphate nanorods are a novel fluorescent label in cell biology

Potential Biomedical Applications of Terbium-Based Nanoparticles (TbNPs): A Review on Recent Advancement

The scientific world is increasingly focusing on rare earth metal oxide nanomaterials due to their consequential biological prospects, navigated by breakthroughs in biomedical applications. Terbium belongs to rare earth elements (lanthanide series) and possesses remarkably strong luminescence at lower energy emission and signal transduction properties, ushering in wide applications for diagnostic measurements (i.e., bioimaging, biosensors, fluorescence imaging, etc.) in the biomedical sectors. In addition, the theranostic applications of terbium-based nanoparticles further permit the targeted delivery of drugs to the specific site of the disease. Furthermore, the antimicrobial properties of terbium nanoparticles induced via reactive oxygen species (ROS) cause oxidative damage to the cell membrane and nuclei of living organisms, ion release, and surface charge interaction, thus further creating or exhibiting excellent antioxidant characteristics. Moreover, the recent applications of terbium nanoparticles in tissue engineering, wound healing, anticancer activity, etc., due to angiogenesis, cell proliferation, promotion of growth factors, biocompatibility, cytotoxicity mitigation, and anti-inflammatory potentials, make this nanoparticle anticipate a future epoch of nanomaterials. Terbium nanoparticles stand as a game changer in the realm of biomedical research, proffering a wide array of possibilities, from revolutionary imaging techniques to advanced drug delivery systems. Their unique properties, including luminescence, magnetic characteristics, and biocompatibility, have redefined the boundaries of what can be achieved in biomedicine. This review primarily delves into various mechanisms involved in biomedical applications via terbium-based nanoparticles due to their physicochemical characteristics. This review article further explains the potential biomedical applications of terbium nanoparticles with in-depth significant mechanisms from the individual literature. This review additionally stands as the first instance to furnish a "single-platted" comprehensive acquaintance of terbium nanoparticles in shaping the future of healthcare as well as potential limitations and overcoming strategies that require exploration before being trialed in clinical settings.

Crystallization, Luminescence and Cytocompatibility of Hexagonal Calcium Doped Terbium Phosphate Hydrate Nanoparticles

Luminescent lanthanide-containing biocompatible nanosystems represent promising candidates as nanoplatforms for bioimaging applications. Herein, citrate-functionalized calcium-doped terbium phosphate hydrate nanophosphors of the rhabdophane type were prepared at different synthesis times and different Ca2+/Tb3+ ratios by a bioinspired crystallization method consisting of thermal decomplexing of Ca2+/Tb3+/citrate/phosphate/carbonate solutions. Nanoparticles were characterized by XRD, TEM, SEM, HR-TEM, FTIR, Raman, Thermogravimetry, inductively coupled plasma spectroscopy, thermoanalysis, dynamic light scattering, electrophoretic mobility, and fluorescence spectroscopy. They displayed ill-defined isometric morphologies with sizes ≤50 nm, hydration number n ~ 0.9, tailored Ca2+ content (0.42-8.11 wt%), and long luminescent lifetimes (800-2600 µs). Their relative luminescence intensities in solid state are neither affected by Ca2+, citrate content, nor by maturation time for Ca2+ doping concentration in solution below 0.07 M Ca2+. Only at this doping concentration does the maturation time strongly affect this property, decreasing it. In aqueous suspensions, neither pH nor ionic strength nor temperature affect their luminescence properties. All the nanoparticles displayed high cytocompatibility on two human carcinoma cell lines and cell viability correlated positively with the amount of doping Ca2+. Thus, these nanocrystals represent promising new luminescent nanoprobes for potential biomedical applications and, if coupled with targeting and therapeutic moieties, they could be effective tools for theranostics.

Lanthanide phosphate (LnPO4 ) rods as bio-probes: A systematic investigation on structural, optical, magnetic, and biological characteristics

The proposed work involves an exclusive study on the synthesis protocol, crystal structure analysis, and imaging contrast features of unique lanthanide phosphates (LnPO₄ ). XRD and Raman spectra affirmed the ability of the proposed synthesis technique to achieve unique LnPO₄ devoid of impurities. The crystal structure analysis confirms the P121/c1 space setting of NdPO₄ , EuPO₄ , GdPO₄ , and TbPO₄ that all uniformly crystallizes in monoclinic unit cell. In a similar manner, the tetragonal crystal setting of DyPO₄ , ErPO₄ , HoPO₄ , and YbPO₄ that unvaryingly possess the I41/amd space setting is confirmed. Under the same synthesis conditions, the monoclinic (Eu) and tetragonal (Ho) lanthanide phosphates displayed uniform rod-like morphologies. Absorption and luminescence properties of unique LnPO₄ were determined. In vitro biological studies demonstrated low toxicity levels of LnPO₄ and clearly distinguished fluorescence of TbPO₄ and EuPO₄ in Y79, retinoblastoma cell lines. The paramagnetic response of GdPO₄ , NdPO₄ , DyPO₄ , TbPO₄ , and HoPO₄ facilitated excellent magnetic resonance imaging (MRI) contrast features. Meanwhile, GdPO₄ , DyPO₄ , HoPO₄ , and YbPO₄ possessing higher X-ray absorption coefficient than clinical contrast Omnipaque™ exhibited high computed tomography (CT) efficiency. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1372-1383, 2019.

Eu/Tb codoped spindle-shaped fluorinated hydroxyapatite nanoparticles for dual-color cell imaging

Lanthanide doped fluorinated hydroxyapatite (FAp) nanoparticles are promising cell imaging nanomaterials but they are excited at wavelengths which do not match the light sources usually found in a commercial confocal laser scanning microscope (CLSM). In this work, we have successfully prepared spindle-shaped Eu/Tb codoped FAp nanoparticles by a hydrothermal method. Compared with single Eu doped FAp, Eu/Tb codoped FAp can be excited by a 488 nm laser, and exhibit both green and red light emission. By changing the amounts of Eu and Tb peaks, the emission in the green region (500-580 nm) can be decreased to the benefit of the emission in the red region (580-720 nm), thus reaching a balanced dual color emission. Using MC3T3-E1 cells co-cultured with Eu/Tb codoped FAp nanoparticles, it is observed that the nanoparticles are cytocompatible even at a concentration as high as 800 μg ml(-1). The Eu/Tb codoped FAp nanoparticles are located in the cytoplasm and can be monitored by dual color-green and red imaging with a single excitation light at 488 nm. At a concentration of 200 μg ml(-1), the cytoplasm is saturated in 8 hours, and Eu/Tb codoped FAp nanoparticles retain their fluorescence for at least 3 days. The cytocompatible Eu/Tb codoped FAp nanoparticles with unique dual color emission will be of great use for cell and tissue imaging.

Probing highly luminescent europium-doped lanthanum orthophosphate nanorods for strategic applications

Herein we have established a strategy for the synthesis of highly luminescent and biocompatible europium-doped lanthanum orthophosphate (La0.85PO4Eu0.15(3+)) nanorods. The structure and morphogenesis of these nanorods have been probed by XRD, SEM, and TEM/HRTEM techniques. The XRD result confirms that the as-synthesized nanorods form in a monazite phase with a monoclinic crystal structure. Furthermore, the surface morphology shows that the synthesized nanorods have an average diameter of ∼90 nm and length of ∼2 μm. The HRTEM images show clear lattice fringes that support the presence of better crystal quality and enhanced photoluminescence hypersensitive red emission at 610 nm ((5)D0-(7)F2) upon 394 nm wavelength excitation. Furthermore, time-resolved spectroscopy and an MTT assay of these luminescent nanorods demonstrate a photoluminescent decay time of milliseconds with nontoxic behavior. Hence, these obtained results suggest that the as-synthesized luminescent nanorods could be potentially used in invisible security ink and high-contrast bioimaging applications.

Size-dependent MRI relaxivity and dual imaging with Eu0.2Gd0.8PO4·H2O nanoparticles

Three different sizes of Eu0.2Gd0.8PO4·H2O nanoparticles have been prepared to investigate the particle size influence on water proton relaxivity. Longitudinal relaxivity (r1) values increase for smaller particles, reaching as high as r1 = 6.13 mM(-1) s(-1) for a sample of 40 ± 4 nm particles, which, with a ratio of transverse/longitudinal relaxivity, r2/r1 = 1.27, are shown to be effective positive contrast agents. The correlation between relaxivity and the surface-to-volume ratio implies that access to surface Gd(3+) sites is the principal factor affecting relaxivity. On the other hand, although ionic molar relaxivity decreases for larger particles, the relaxivity per particle can be significantly greater. Gadolinium-based nanoparticles doped with fluorescent lanthanide elements have attracted attention for their dual-imaging abilities, combining magnetic resonance imaging (MRI) and fluorescence imaging agents. In both in vitro experiments with HeLa cells and in vivo experiments with C. elegans, strong red fluorescence is observed from Eu0.2Gd0.8PO4·H2O with high resolution, demonstrating the parallel use of the particles as fluorescence imaging agents.

Energy-transfer from Gd(III) to Tb(III) in (Gd,Yb,Tb)PO4 nanocrystals

The photoluminescence properties of (Gd,Yb,Tb)PO4 nanocrystals synthesized via a hydrothermal route at 150 °C are reported. Energy-transfer from Gd(3+) to Tb(3+) is witnessed by the detailed analyses of excited-state lifetimes, emission quantum yields, and emission and excitation spectra at room temperature, for Tb(3+) concentrations ranging from 0.5 to 5.0 mol%. Absolute-emission quantum yields up to 42% are obtained by exciting within the (6)I7/2-17/2 (Gd(3+)) manifold at 272 nm. The room temperature emission spectrum is dominated by the (5)D4 → (7)F5 (Tb(3+)) transition at 543 nm, with a long decay-time (3.95-6.25 ms) and exhibiting a rise-time component. The (5)D3 → (7)F6 (Tb(3+)) rise-time (0.078 ms) and the (6)P7/2 → (8)S7/2 (Gd(3+)) decay-time (0.103 ms) are of the same order, supporting the Gd(3+) to Tb(3+) energy-transfer process. A remarkably longer lifetime of 2.29 ms was measured at 11 K for the (6)P7/2 → (8)S7/2 (Gd(3+)) emission upon excitation at 272 nm, while the emission spectrum at 11 K is dominated by the (6)P7/2 → (8)S7/2 transition line, showing that the Gd(3+) to Tb(3+) energy-transfer process is mainly phonon-assisted with an efficiency of ~95% at room temperature. The Gd(3+) to Tb(3+) energy transfer is governed by the exchange mechanism with rates between 10(2) and 10(3) s(-1), depending on the energy mismatch conditions between the (6)I7/2 and (6)P7/2 levels of Gd(3+) and the Tb(3+ 5)I7, (5)F2,3 and (5)H5,6,7 manifolds and the radial overlap integral values.

A microwave-assisted solution combustion synthesis to produce europium-doped calcium phosphate nanowhiskers for bioimaging applications

Biocompatible nanoparticles possessing fluorescent properties offer attractive possibilities for multifunctional bioimaging and/or drug and gene delivery applications. Many of the limitations with current imaging systems center on the properties of the optical probes in relation to equipment technical capabilities. Here we introduce a novel high aspect ratio and highly crystalline europium-doped calcium phosphate nanowhisker produced using a simple microwave-assisted solution combustion synthesis method for use as a multifunctional bioimaging probe. X-ray diffraction confirmed the material phase as europium-doped hydroxyapatite. Fluorescence emission and excitation spectra and their corresponding peaks were identified using spectrofluorimetry and validated with fluorescence, confocal and multiphoton microscopy. The nanowhiskers were found to exhibit red and far red wavelength fluorescence under ultraviolet excitation with an optimal peak emission of 696 nm achieved with a 350 nm excitation. Relatively narrow emission bands were observed, which may permit their use in multicolor imaging applications. Confocal and multiphoton microscopy confirmed that the nanoparticles provide sufficient intensity to be utilized in imaging applications.

(Gd,Yb,Tb)PO4 up-conversion nanocrystals for bimodal luminescence-MR imaging

Up-conversion (Gd,Yb,Tb)PO(4) materials and their potential for bimodal imaging have received little attention in the literature. Herein, we report the first study on the up-conversion emission of (Gd,Yb,Tb)PO(4) nanocrystals synthesized via a hydrothermal method at 150 °C. These materials exhibit ultraviolet, blue and green up-conversion emissions upon excitation with a 980 nm continuous wave laser diode. The intensity of the blue-emission band at 479 nm, ascribed to the cooperative up-conversion emission of a pair of excited Yb(3+) ions, depends on the Yb(3+)/Tb(3+) concentration ratio, calcination temperature and particle size. Strong green up-conversion emission of Tb(3+) is observed at 543 nm for the (5)D(4)→(7)F(5) transition. Relaxometry measurements reveal that the nanocrystals are efficient T(2)-weighted (negative) contrast agents which, combined with visible-light emission generated by infrared excitation, affords them considerable potential for being used in bimodal, photoluminescence-magnetic resonance, imaging.

Development of a multilevel approach for the evaluation of nanomaterials' toxicity

AIM

To develop a multilevel approach that includes different toxicity tests and gene-expression studies for toxicity evaluation of engineered nanomaterials developed for biomedical applications.

MATERIALS & METHODS

K-562, MCF-7 and U-937 human-derived cell lines were used as models for in vitro toxicity tests. These tests included viability assays (3-[4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium [MTS] assay); evaluation of apoptosis/necrosis by propidium iodide staining and DNA laddering assay; evaluation of mitochondrial toxicity (5,5´,6,6´-tetrachloro-1,1´,3,3´-tetraethyl-benzimidazolcarbocyanine iodide [JC-1] assay); transmission electron microscopy analysis and gene expression analysis by DNA microarray. For in vivo toxicity evaluation, Swiss mice were used for monitoring acute or chronic effects. Two superparamagnetic contrast agents approved for human use (Resovist and Primovist) and two new lanthanide-based luminescent nanoparticles were tested.

RESULTS & DISCUSSION

The nanomaterials approved for human use did not show significant toxicities in our assays. Toxicity studies performed on lanthanide-based nanoparticles (EDTA120 and EDTA120D) complexed with the chelating agent EDTA revealed that these nanomaterials induced necrosis in U-937 and K-562 cells while no toxicity was observed in MCF-7 cells. Moreover, no in vivo effects have been observed. The comparative analysis of the nanomaterials and their separated components showed that the toxicity in U-937 and K-562 cells was mainly due to the presence of EDTA.

CONCLUSION

The multilevel approach proved to be useful for nanomaterial toxicity characterization. In particular, for the lanthanide-based nanoparticles tested in this work, the EDTA was identified as the main cause of the toxicity in vitro, suggesting a possible applicability of these nanoparticle suspensions for in vivo optical imaging.

A study of graphene films synthesized on nickel substrates: existence and origin of small-base-area peaks

Large-area graphene films, synthesized by the chemical vapor deposition (CVD) method, have the potential to be used as electrodes. However, the electrical properties of CVD-synthesized graphene films fall short of the best results obtained for graphene films prepared by other methods. Therefore, it is important to understand the reason why these electrical properties are inferior to improve the applicability of CVD-grown graphene films. Here, we show that CVD-grown graphene films on nickel substrates contain many small-base-area (SBA) peaks that scatter conducting electrons, thereby decreasing the Hall mobility of charges in the films. These SBA peaks were induced by small peaks on the nickel surface and are likely composed of amorphous carbon. The formation of these SBA peaks on graphene films was successfully suppressed by controlling the surface morphology of the nickel substrate. These findings may be useful for the development of a CVD synthesis method that is capable of producing better quality graphene films with large areas.

Fabrication and characterization of an inorganic gold and silica nanoparticle mediated drug delivery system for nitric oxide

Nitric oxide (NO) plays an important role in inhibiting the development of hepatic fibrosis and its ensuing complication of portal hypertension by inhibiting human hepatic stellate cell (HSC) activation. Here we have developed a gold nanoparticle and silica nanoparticle mediated drug delivery system containing NO donors, which could be used for potential therapeutic application in chronic liver disease. The gold nanoconjugates were characterized using several physico-chemical techniques such as UV-visible spectroscopy and transmission electron microscopy. Silica nanoconjugates were synthesized and characterized as reported previously. NO released from gold and silica nanoconjugates was quantified under physiological conditions (pH = 7.4 at 37 degrees C) for a substantial period of time. HSC proliferation and the vascular tube formation ability, manifestations of their activation, were significantly attenuated by the NO released from these nanoconjugates. This study indicates that gold and silica nanoparticle mediated drug delivery systems for introducing NO could be used as a strategy for the treatment of hepatic fibrosis or chronic liver diseases, by limiting HSC activation.

Ambient large-scale template-mediated synthesis of high-aspect ratio single-crystalline, chemically doped rare-earth phosphate nanowires for bioimaging

A simple and effective template-mediated protocol has been developed for the large-scale, room-temperature preparation of high-aspect-ratio, single-crystalline Tb-doped CePO(4) nanowires, measuring approximately 12 nm in diameter and over 10 mum in length. Moreover, we also isolated sheaf-like bundles of nanostructures. The synthesis mechanism likely involved a crystal splitting step. The resulting nanowires demonstrated an intense redox-sensitive green photoluminescence, which was exploited, in addition to their inherently high biocompatibility and low toxicity, for potential applications in biological imaging and labeling of cells.

In vivo toxicity studies of europium hydroxide nanorods in mice

Lanthanide nanoparticles and nanorods have been widely used for diagnostic and therapeutic applications in biomedical nanotechnology due to their fluorescence and pro-angiogenic properties to endothelial cells, respectively. Recently, we have demonstrated that europium (III) hydroxide [Eu(III)(OH)(3)] nanorods, synthesized by the microwave technique and characterized by several physico-chemical techniques, can be used as pro-angiogenic agents which introduce future therapeutic treatment strategies for severe ischemic heart/limb disease, and peripheral ischemic disease. The toxicity of these inorganic nanorods to endothelial cells was supported by several in vitro assays. To determine the in vivo toxicity, these nanorods were administered to mice through intraperitoneal injection (IP) everyday over a period of seven days in a dose dependent (1.25 to 125 mg kg(-1) day(-1)) and time dependent manner (8-60 days). Bio-distribution of europium elements in different organs was analyzed by inductively coupled plasma mass spectrometry (ICPMS). Short-term (S-T) and long-term (L-T) toxicity studies (mice euthanized on days 8 and 60 for S-T and L-T, respectively) show normal blood hematology and serum clinical chemistry with the exception of a slight elevation of liver enzymes. Histological examination of nanorod-treated vital organs (liver, kidney, spleen and lungs) showed no or only mild histological changes that indicate mild toxicity at the higher dose of nanorods.

NanoGenotoxicology: the DNA damaging potential of engineered nanomaterials

With the rapid expansion in the nanotechnology industry, it is essential that the safety of engineered nanomaterials and the factors that influence their associated hazards are understood. A vital area governing regulatory health risk assessment is genotoxicology (the study of genetic aberrations following exposure to test agents), as DNA damage may initiate and promote carcinogenesis, or impact fertility. Of late, considerable attention has been given to the toxicity of engineered nanomaterials, but the importance of their genotoxic potential on human health has been largely overlooked. This comprehensive review focuses on the reported abilities of metal nanoparticles, metal-oxide nanoparticles, quantum dots, fullerenes, and fibrous nanomaterials, to damage or interact with DNA, and their ecogenotoxicity is also considered. Many of the engineered nanomaterials assessed were found to cause genotoxic responses, such as chromosomal fragmentation, DNA strand breakages, point mutations, oxidative DNA adducts and alterations in gene expression profiles. However, there are clear inconsistencies in the literature and it is difficult to draw conclusions on the physico-chemical features of nanomaterials that promote genotoxicity, largely due to study design. Hence, areas that require that further attention are highlighted and recommendations to improve our understanding of the genotoxic potential of engineered nanomaterials are addressed.

Facile preparation of self-assembled hydrogel-like GdPO4*H2O nanorods

Of the methods employed in the preparation of one-dimensional lanthanide phosphate (LnPO(4)) nanorods/nanowires, such as GdPO(4), the hydrothermal method has been mainly used as a synthetic route. In this study, we report a facile low-temperature solution approach to prepare GdPO 4*H(2)O nanorods by simply refluxing GdCl(3) and KH(2)PO(4) for only 15 min at 88 degrees C, an approach that can easily be scaled up by increasing the reagent amounts. We observed a highly viscous macroscopic hydrogel-like material when we mixed as-prepared GdPO(4)*H(2)O nanomaterials with H(2)O. Hydrogels are an important class of biomaterials. Their building blocks, normally formed from protein-, peptide-, polymer-, and lipid-based materials, offer three-dimensional scaffolds for drug delivery, tissue engineering, and biosensors. Our preliminary results showed that GdPO(4)*H(2)O hydrogels could be used for encapsulation and drug release, and that they were biocompatible, acting as scaffolds to foster cell proliferation. These findings suggested that they might have biomedical uses. Our findings may lead to the creation of other inorganic nanomaterial-based hydrogels apart from the organic and biomolecular protein-, peptide-, polymer-, and lipid-based building blocks.

Functionalized europium nanorods for in vitro imaging

Emissive europium hydroxide nanorods (ENR) (20 nm x 500 nm) functionalized by a surface coating of chromophore-containing organically modified silicate (ORMOSIL) layer, have been synthesized and characterized by high-resolution transmission electron microscopy (TEM). Low-temperature photophysical characterization of the functionalized nanorods (FENR) demonstrated a strong red 5D0 luminescence both in solid and in suspended solutions. Potentials of this nanorod material for live cell imaging have also been explored. Both the bare and functionalized nanorods are able to enter living human cells with no discernible cytotoxicity. Chromophore-to-Eu3+ energy-transfer in the functionalized nanorods enables staining of the cytoplasm of living human cells. This is confirmed by costaining with fluorescent dextran. The red chromophore-sensitized luminescence from the internalized nanorods in live human lung carcinoma cells (A549) can be observed by confocal microscopy 2 h after loading and reaches maximal emission after 24 h.