Biofunctionalization of Fluorescent Rare-Earth-Doped Lanthanum Phosphate Colloidal Nanoparticles

Pressure-induced photoluminescence enhancement of CeF3:Tb3+ nanoparticles

Rare earth fluorides have been widely used in recent years in the field of solid-state lighting. However, the relationship between the structure and luminescence properties is still unclear. Herein, the photoluminescence and structural transition of CeF3:Tb3+ nanoparticles under high pressure were investigated through in situ photoluminescence and X-ray diffraction measurements. Intriguingly, the photoluminescence of CeF3:Tb3+ nanoparticles displays an enhancement from 18.3 to 33.4 GPa, accompanied by the phase transition from the starting hexagonal phase to the orthorhombic phase. It was found that the distance of luminescent centers increased sharply during the high-pressure phase transition, which weakened the quenching effect and improved transmission efficiency. Our work provides more insight into the optical characteristics and structures of rare earth trifluorides.

Rare earth smart nanomaterials for bone tissue engineering and implantology: Advances, challenges, and prospects

Bone grafts or prosthetic implant designing for clinical application is challenging due to the complexity of integrated physiological processes. The revolutionary advances of nanotechnology in the biomaterial field expedite and endorse the current unresolved complexity in functional bone graft and implant design. Rare earth (RE) materials are emerging biomaterials in tissue engineering due to their unique biocompatibility, fluorescence upconversion, antimicrobial, antioxidants, and anti-inflammatory properties. Researchers have developed various RE smart nano-biomaterials for bone tissue engineering and implantology applications in the past two decades. Furthermore, researchers have explored the molecular mechanisms of RE material-mediated tissue regeneration. Recent advances in biomedical applications of micro or nano-scale RE materials have provided a foundation for developing novel, cost-effective bone tissue engineering strategies. This review attempted to provide an overview of RE nanomaterials' technological innovations in bone tissue engineering and implantology and summarized the osteogenic, angiogenic, immunomodulatory, antioxidant, in vivo bone tissue imaging, and antimicrobial properties of various RE nanomaterials, as well as the molecular mechanisms involved in these biological events. Further, we extend to discuss the challenges and prospects of RE smart nano-biomaterials in the field of bone tissue engineering and implantology.

Tunable multicolor and bright white emission in PEG modified β-NaGdF4 nanocrystals by systematic introduction of Ce3+ and Mn2+/Ln3+

In this paper, Mn²⁺/Ln³⁺-doped hexagonal phase (β-) NaGdF₄:Ce (Ln = Tb, Dy, Eu) nanomaterials with subtly tuned multicolor output have been successfully synthesized by a typical simple hydrothermal method using polyethylene glycol (PEG) as a surface modifying agent. The crystal structures, morphology, luminescence performance, and energy transfer (ET) mechanism of the synthesized NaGdF₄ nanoparticles (NPs) were investigated in detail. It is found that due to the effective ET between Ce³⁺ and Mn²⁺/Ln³⁺, the multicolor down-conversion (DC) emission phosphors can yield three major emission bands in the visible region including blue, green and red. Moreover, the white emission could be realized through manipulating the doping ratio of Ce³⁺, Dy³⁺ and Eu³⁺ with suitable concentration in β-NaGdF₄ NPs through effective resonance-type ET under the irradiation of 273 nm. And the corresponding CIE1931 coordinates were calculated to be (0.31, 0.32), which is near the normative white emission (0.33, 0.33). All the multicolor tuning and white emission results evidently suggest that the present Ce³⁺ and Mn²⁺/Ln³⁺-doped β-NaGdF₄ NPs are feasible phosphors for potential applications in white-light emitters, full-color displays and photonic devices.

Effective multicolor and strong white light emission were realized in NaGdF₄:Ce NPs by precisely adjusted the doping amounts of Dy³⁺ and Eu³⁺.

Influence of Terbium Ions and Their Concentration on the Photoluminescence Properties of Hydroxyapatite for Biomedical Applications

A new generation of biomaterials with terbium-doped hydroxyapatite was obtained using a coprecipitation method. The synthesis of new materials with luminescent properties represents a challenging but important contribution due to their potential applications in biomedical science. The main objective of this study was to revel the influence of terbium ions on the design and structure of hydroxyapatite. Different concentrations of terbium, described by the chemical formula Ca_10−xTb_x(PO₄)₆(OH)₂, where x is in the range of 0 to 1, were considered. The consequence of ion concentration on hydroxyapatite morphology was also investigated. The morphology and structure, as well as the optical properties, of the obtained nanomaterials were characterized using X-ray powder diffraction analysis (XRD), Fourier Transform Infrared spectrometry (FTIR), SEM and TEM microscopy, UV-Vis and photoluminescence spectroscopies. The measurements revealed that terbium ions were integrated into the structure of hydroxyapatite within certain compositional limits. The biocompatibility and cytotoxicity of the obtained powders evaluated using MTT assay, oxidative stress assessment and fluorescent microscopy revealed the ability of the synthesized nanomaterials to be used for biological system imaging.

Physiochemical characterization of highly biocompatible, and colloidal LaF3:Yb/Er upconversion nanoparticles

Highly colloidal upconversion nanoparticles (UCNPs) were synthesized at low temperatures by the thermal decomposition process. The structure, morphology, crystallinity, surface chemistry, and optical properties were systematically optimized and studied through various spectroscopic techniques. X-ray diffraction (XRD) patterns have shown the formation of single-phase, highly purified, well-crystalline, hexagonal LaF₃ NPs, while the TEM micrographs show small, irregular sizes, spherically shaped, and aggregated polycrystalline UCNPs with an average crystalline size of about 8-15 nm. The Negative Zeta Potential value exhibits good biocompatibility of the UCNPs, which supports the idea that surface-anchored hydroxyl groups facilitate the stabilization of the NPs in aqueous media, as well as enhance biomolecules' tagging efficiency. The absorption spectrum, Zeta Potential, and hydrodynamic size that were measured in aqueous media illustrate excellent dispersibility, colloidal stability, biocompatibility, and cytotoxicity character of the UCNPs. Zeta potential and MTT assay studies illustrated high biocompatibility, it could be due to the surface-anchored hydroxyl groups. The nanoproduct demonstrates an excellent UC luminescence spectrum (i.e., prominent green emission ⁴S_3/2 → ⁴I/_15/2) upon irradiation by the 980-nm laser diode. TEM micrographs, further, revealed that this optically active material with aqueous sensitivities, porous crystal structure, and excellent UCNPs, could be a favorable candidate for potential photonics-based bio-related applications.

PEG-Neridronate-Modified NaYF4:Gd3+,Yb3+,Tm3+/NaGdF4 Core-Shell Upconverting Nanoparticles for Bimodal Magnetic Resonance/Optical Luminescence Imaging

Upconverting nanoparticles are attracting extensive interest as a multimodal imaging tool. In this work, we report on the synthesis and characterization of gadolinium-enriched upconverting nanoparticles for bimodal magnetic resonance and optical luminescence imaging. NaYF4:Gd3+,Yb3+,Tm3+ core upconverting nanoparticles were obtained by a thermal coprecipitation of lanthanide oleate precursors in the presence of oleic acid as a stabilizer. With the aim of improving the upconversion emission and increasing the amount of Gd3+ ions on the nanoparticle surface, a 2.5 nm NaGdF4 shell was grown by the epitaxial layer-by-layer strategy, resulting in the 26 nm core-shell nanoparticles. Both core and core-shell nanoparticles were coated with poly(ethylene glycol) (PEG)-neridronate (PEG-Ner) to have stable and well-dispersed upconverting nanoparticles in a biological medium. FTIR spectroscopy and thermogravimetric analysis indicated the presence of ∼20 wt % of PEG-Ner on the nanoparticle surface. The addition of inert NaGdF4 shell resulted in a total 26-fold enhancement of the emission under 980 nm excitation and also affected the T 1 and T 2 relaxation times. Both r 1 and r 2 relaxivities of PEG-Ner-modified nanoparticles were much higher compared to those of non-PEGylated particles, thus manifesting their potential as a diagnostic tool for magnetic resonance imaging. Together with the enhanced luminescence efficiency, upconverting nanoparticles might represent an efficient probe for bimodal in vitro and in vivo imaging of cells in regenerative medicine, drug delivery, and/or photodynamic therapy.

High-efficient fabrication of core-shell-shell structured SiO2@GdPO4:Tb@SiO2 nanoparticles with improved luminescence

SiO₂@GdPO₄:Tb@SiO₂ nanoparticles with core-shell-shell structure were successfully synthesized by a cheap silane coupling agent grafting method at room temperature. This method not only homogeneously coated rare-earth phosphate nanoparticles on the surface of silica spheres but also saved the use of rare-earth resources. The obtained nanoparticles consisted of SiO₂ core with a diameter of approximately 210 nm, GdPO₄:Tb intermediate shell with thickness of approximately 7 nm, and SiO₂ outer shell with thickness of approximately 20 nm. This unique core-shell-shell structured nanoparticles exhibited strong luminescence properties compared with GdPO₄:Tb nanoparticles. The core-shell-shell structured nanoparticles can effectively quench the intrinsic fluorescence of bovine serum albumin through a static quenching mode. The as-synthesized nanoparticles show great potential in biological cell imaging and cancer treatment.

Hydrothermal synthesis of BaLu2F8:Ln3+ crystals: phase/morphology evolution, energy transfer and tunable multicolor luminescence

BaLu_2−xF₈:xLn³⁺ crystals have been synthesized via a one-step hydrothermal route without any surfactants.

Impact of particle size, oxidation state and capping agent of different cerium dioxide nanoparticles on the phosphate-induced transformations at different pH and concentration

The potential hazard posed by nanomaterials can be significantly influenced by transformations which these materials undergo during their lifecycle, from manufacturing through to disposal. The transformations may depend on the nanomaterials’ own physicochemical properties as well as the environment they are exposed to. This study focuses on the mechanisms of transformation of cerium oxide nanoparticles (CeO₂ NPs) in laboratory experiments which simulate potential scenarios in which the NPs are exposed to phosphate-bearing media. We have experimented with the transformation of four different kinds of CeO₂ NPs, in order to investigate the effects of nanoparticle size, capping agent (three were uncapped and one was PVP capped) and oxidation state (two consisted mostly of Ce⁴⁺ and two were a mix of Ce^3+/Ce⁴⁺). They were exposed to a reaction solution containing KH₂PO₄, citric acid and ascorbic acid at pH values of 2.3, 5.5 and 12.3, and concentrations of 1mM and 5mM. The transformations were followed by UV-vis, zeta potential and XRD measurements, which were taken after 7 and 21 days, and by transmission electron microscopy after 21 days. X-ray photoelectron spectroscopy was measured at 5mM concentration after 21 days for some samples. Results show that for pH 5 and 5mM phosphate concentration, CePO₄ NPs were formed. Nanoparticles that were mostly Ce⁴⁺ did not dissolve at 1mM reagent concentration, and did not produce CePO₄ NPs. When PVP was present as a capping agent it proved to be an extra reducing agent, and CePO₄ was found under all conditions used. This is the first paper where the transformation of CeO₂ NPs in the presence of phosphate has been studied for particles with different size, shapes and capping agents, in a range of different conditions and using many different characterisation methods.

Super metal hydrogels constructed from a simple tripodal gelator and rare earth metal ions and its application in highly selective and ultrasensitive detection of histidine

A series of stable super metal hydrogels (TP-Ms, M = Tb3+, Eu3+, La3+ and Ce3+) with a low critical gelation concentration (2.28 × 10-3 M, 0.1%) was successfully constructed by forming hierarchical assemblies of a tripodal gelator (TP) with rare earth metal ions (Tb3+, Eu3+, La3+ and Ce3+). Interestingly, the super metal hydrogels TP-Eu and TP-La show a specific and ultrasensitive response to histidine (His). The addition of a series of amino acids into the metal hydrogels TP-Eu and TP-La showed that only His could induce distinct fluorescent enhancement for TP-Eu and TP-La, while other amino acids did not significantly interfere with the His sensing process. The LODs of super metal-hydrogel TP-Eu and TP-La for His are (1.83-1.94) × 10-9 and (1.83-1.85) × 10-9 M, respectively. In addition, constructing super supramolecular metal hydrogels by hierarchical assemblies of an easily synthesized tripodal gelator and rare earth metal ions is a novel and efficient approach to the design and development of multi-functional super supramolecular metal hydrogel-based materials.

Surface Functionalisation of Upconversion Nanoparticles with Different Moieties for Biomedical Applications

Lanthanide ion-doped upconversion nanoparticles (UCNPs) that can convert low-energy infrared photons into high-energy visible and ultraviolet photons, are becoming highly sought-after for advanced biomedical and biophotonics applications. Their unique luminescent properties enable UCNPs to be applied for diagnosis, including biolabeling, biosensing, bioimaging, and multiple imaging modality, as well as therapeutic treatments including photothermal and photodynamic therapy, bio-reductive chemotherapy and drug delivery. For the employment of the inorganic nanomaterials into biological environments, it is critical to bridge the gap in between nanoparticles and biomolecules via surface modifications and subsequent functionalisation. This work reviews the various ways to surface modify and functionalise UCNPs so as to impart different functional molecular groups to the UCNPs surfaces for a broad range of applications in biomedical areas. We discussed commonly used base functionalities, including carboxyl, amino and thiol moieties that are typically imparted to UCNP surfaces so as to provide further functional capacity.

Pyrophosphate ion-triggered competitive displacement of ssDNA from a metal-organic framework and its application in fluorescent sensing of alkaline phosphatase

Nanomaterial/aptamer assembly has been extensively explored in the detection of various targets, but some limitations still exist in its practical applications, especially time consumption and low-efficient detachment of the aptamer from the nanomaterial surface. In this work, we demonstrated the ligand role of pyrophosphate ion (PPi) in the competitive displacement of ssDNA from the nanoscaffold surface. For this purpose, a fluorescein-labeled ssDNA (F-DNA) and a mixed valence state cerium (Ce³⁺/Ce⁴⁺)-based MOF (MVCM) were employed as the signal response unit and nanoscaffold, respectively. Benefiting from the existence of Ce⁴⁺, the MVCM exhibits an ultrahigh quenching efficiency (more than 90%) to F-DNA fluorescence, which is 3-fold higher than that of the MOF with Ce³⁺ only. However, it was found that PPi can effectively suppress the quenching effect of the MVCM by competitive coordination with the MVCM to displace F-DNA. Different from the conventional target-induced conformational change of aptamers, the PPi-triggered displacement assay is independent of the ssDNA sequence and can be rapidly completed in just 2 min. The displacement assay is also highly sensitive, even at a PPi concentration as low as 55 nM. In contrast to PPi, however, the phosphate ions and other anions cannot displace F-DNA from the MVCM surface to switch on the F-DNA fluorescence. Inspired by this fact, the PPi-triggered displacement assay was further applied in the detection of alkaline phosphatase (ALP). The detection limit toward ALP was obtained at 0.18 mU mL^-1. Moreover, the accurate determination of ALP concentration in serum samples indicates the applicability of this sensing system in detecting real samples.

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.

Mercury Speciation with Fluorescent Gold Nanocluster as a Probe

Fluorescent nanoparticles are widely used for sensing biologically significant species. However, there are only rare reports of the discrimination or speciation of metal species. In this work, we report for the first time the speciation of mercury (Hg²⁺) and methylmercury (CH₃Hg⁺) by taking advantage of the fluorescence feature of folic-acid-capped gold nanoclusters (FA-AuNCs). FA-Au NCs exhibit an average size of 2.08 ± 0.15 nm and a maximum emission at λ_ex/λ_em = 280/440 nm with a quantum yield of 27.3%. It is interesting that Hg²⁺ causes a significant quench of the fluorescence of FA-Au NCs, whereas CH₃Hg⁺ leads to a remarkable fluorescence enhancement. On the basis of this discriminative fluorescent response between Hg²⁺ and CH₃Hg⁺, a novel nanosensor for the speciation of CH₃Hg⁺ and Hg²⁺ was developed, providing limits of detection (LODs) of 28 nM for Hg²⁺ and 25 nM for CH₃Hg⁺ within 100-1000 nM. This sensing system is highly selective to mercury. Its practical applications were further demonstrated by the analysis of CH₃Hg⁺ and the speciation of mercury (CH₃Hg⁺ and Hg²⁺) in environmental water and fish samples.

Temperature-Responsive Hydrogel-Coated Gold Nanoshells

Gold nanoshells (~160 nm in diameter) were encapsulated within a shell of temperature-responsive poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) using a surface-bound rationally-designed free radical initiator in water for the development of a photothermally-induced drug-delivery system. The morphologies of the resultant hydrogel-coated nanoshells were analyzed by scanning electron microscopy (SEM), while the temperature-responsive behavior of the nanoparticles was characterized by dynamic light scattering (DLS). The diameter of the P(NIPAM-co-AA) encapsulated nanoshells decreased as the solution temperature was increased, indicating a collapse of the hydrogel layer with increasing temperatures. In addition, the optical properties of the composite nanoshells were studied by UV-visible spectroscopy. The surface plasmon resonance (SPR) peak of the hydrogel-coated nanoshells appeared at ~800 nm, which lies within the tissue-transparent range that is important for biomedical applications. Furthermore, the periphery of the particles was conjugated with the model protein avidin to modify the hydrogel-coated nanoshells with a fluorescent-tagged biotin, biotin-4-fluorescein (biotin-4-FITC), for colorimetric imaging/monitoring.

Enhanced hydrothermal crystallization and color tailorable photoluminescence of hexagonal structured YPO4:Sm/Tb nanorods

Mal²⁻ and superfluous PO₄³⁻ jointly ensured the hydrothermal crystallization of hexagonal structured YPO₄:Tb/Sm nanorods with color-tailorable photoluminescence and large aspect ratios of up to ∼32.

Recent progress in upconversion luminescence nanomaterials for biomedical applications

This review focuses on the biomedical applications of upconversion luminescence nanomaterials, including lanthanide-doped inorganic nanocrystals and TTA-based UCNPs.

Luminescence and thermal stability enhancement by matrix luminescence center dispersion in Sc(V, P)O4: Dy3+ nano/submicron phosphors

We report on the luminescence and thermal stability enhancement by the matrix luminescence center dispersion.

Synthesis and luminescent properties of uniform monodisperse LuPO4:Eu3+/Tb3+ hollow microspheres

Uniform monodisperse LuPO4:Eu3+/Tb3+ hollow microspheres with diameters of about 2.4 µm have been successfully synthesized by the combination of a facile homogeneous precipitation approach, an ion-exchange process and a calcination process. The possible formation mechanism for the hollow microspheres was presented. Furthermore, the luminescence properties revealed that the LuPO4:Eu3+ and LuPO4:Tb3+ phosphors show strong orange-red and green emissions under ultraviolet excitation, respectively, which endows this material with potential application in many fields, such as light display systems and optoelectronic devices. Since the synthetic process can be carried out at mild conditions, it should be straightforward to scale up the entire process for large-scale production of the LuPO4 hollow microspheres. Furthermore, this general and simple method may be of much significance in the synthesis of many other inorganic materials.

Layered Yttrium Hydroxide l-Y(OH)3 Luminescent Adsorbent for Detection and Recovery of Phosphate from Water over a Wide pH Range

Layered yttrium hydroxide, l-Y(OH)₃, has been explored as a representative member of the layered rare earth hydroxide family (l-RE(OH)₃; RE = rare earths) for removal and recovery of phosphate from aqueous solution. Compared to the hexagonal form, h-Y(OH)₃, which has a weakly positive surface charge only at low pH, the layered polymorph composed of hydroxocation layers exhibited a high point of zero charge (pH_pzc ∼ 11) and significantly enhanced adsorptive ability for anions over a wide pH range. The Langmuir isotherm model and pseudo-second-order kinetic model were adopted to explain the phosphate adsorption on l-Y(OH)₃. This new adsorbent revealed high capacity, efficiency, stability, selectivity, and reusability in adsorption of phosphate from a single electrolyte as well as natural waters containing competing anions. Essentially complete phosphate recovery from aqueous solutions at low phosphate concentrations (2.0 mg of P/L) was demonstrated with an adsorbent dosage of 0.025-0.5 g/L. The adsorption of phosphate was accompanied by an increase in the solution pH, suggesting a release of OH^- ions during the adsorption reaction. In particular, when Ce³⁺ and Tb³⁺ were co-doped (l-Y(OH)₃:Ce,Tb), phosphate adsorption led to the characteristic ⁵D₄ → ⁷F_J (J = 6, 5, and 4) emissions of Tb³⁺ under commercial 312 nm UV irradiation. The photoluminescence of phosphate-adsorbed l-Y(OH)₃:Ce,Tb provided evidence of the inner-sphere complexing mechanism involving the formation of Y(Ce,Tb)-O-P bonds through which the energy transfer can occur. The "luminescence-on" behavior of l-Y(OH)₃:Ce,Tb by phosphate adsorption was employed to detect and recover phosphorus at low concentrations in deionized water, mineral water, tap water, and river water.

Emission enhancement through Nd3+-Yb3+ energy transfer in multifunctional NaGdF4 nanocrystals

The growing need for biomedical contrast agents has led to the current development of multi-functional materials such as lanthanide-based nanoparticles (NPs). The optical and magnetic properties these nanoparticles (NPs) possess are important to enhance current biomedical imaging techniques. To increase the optical emissions of the nanoparticles, neodymium (Nd3+) and ytterbium (Yb3+) were introduced into a magnetic host of NaGdF4. The energy transfer between Nd3+ and the Yb3+ was then investigated at multiple concentrations to determine the optimal dopant levels. The NaGdF4:Nd3+,Yb3+ nanoparticles were synthesized through a modified solvothermal method, resulting in rectangular structures, with an average side length of 17.87 ± 4.38 nm. A double dopant concentration of 10% Nd3+ and 4% Yb3+ was found to be optimal, increasing the emission intensity by 71.5% when compared to the widely used Nd3+ single dopant. Decay measurements confirm energy transfer from Nd3+ to Yb3+, with a lifetime shortening from Nd3+ 1064 nm emission and a calculated lifetime of 12.72 ms with 98% efficiency. Despite NaGdF4:Nd3+,Yb3+ NPs showing a slight decrease in their magnetic response at the expense of optimizing optical emission, as it is directly dependent on the Gd3+ concentration, a strong paramagnetic behavior was still observed. These results corroborate that NaGdF4:Nd3+,Yb3+ NPs are viable candidates for multimodal imaging.

Gold and Hairpin DNA Functionalization of Upconversion Nanocrystals for Imaging and In Vivo Drug Delivery

Although multifunctional upconversion imaging probes have recently attracted considerable interest in biomedical research, there are currently few methods for stabilizing these luminescent nanoprobes with oligonucleotides in biological systems. Herein, a method to robustly disperse upconversion nanoprobes in physiological buffers based on rational design and synthesis of nanoconjugates comprising hairpin-DNA-modified gold nanoparticles is presented. This approach imparts the upconversion nanoprobes with excellent biocompatibility and circumvents the problem of particle agglomeration. By combining single-band anti-Stokes near-infrared emission and the photothermal effect mediated by the coupling of gold to upconversion nanoparticles, a simple, versatile nanoparticulate system for simultaneous deep-tissue imaging and drug molecule release in vivo is demonstrated.

Shear Stress Induced Fabrication of Dandelion-Shaped Lanthanide Phosphate Nanoparticles

Lanthanide phosphate nanoparticles were co-precipitated under continuous flow in a vortex fluidic device in the presence of polyvinylpyrrolidone (PVP) of different molecular weights and at varying rotational speeds and tilt angles. Dandelion-shaped lanthanide phosphate particles were produced at rotation speeds of 5000 rpm and 7000 rpm. In contrast, individual rods formed at 9000 rpm. Transition electron microscope images reveal changes in morphology of the dandelion-shaped nanoparticles with changes in the chain length of PVP or tilt angle of the tube of the vortex fluidic device. These morphological changes are likely to arise from different wrapping and aggregation of the nanoparticles induced by the PVP polymer under shear.

Dicarboxylate mediated efficient morphology/phase tailoring of YPO4:Ln3+ crystals and investigation of down-/up-conversion luminescence

Both hexagonal (h-) and tetragonal (t-) structured YPO₄ crystals with multiform morphologies of high uniformity were selectively synthesized by using dicarboxylates as morphology/structure modifiers.

Multimodal imaging and photothermal therapy were simultaneously achieved in the core–shell UCNR structure by using single near-infrared light

Core–shell nanostructures consisting of plasmonic materials and lanthanide-doped upconversion nanoparticles (UCNPs) show promising applications in theranostics including bio-imaging, diagnosis and therapy.

Ultrasensitive Luminescent In Vitro Detection for Tumor Markers Based on Inorganic Lanthanide Nano-Bioprobes

Ultrasensitive and accurate detection of tumor markers is of vital importance for the screening or diagnosis of cancers at their early stages and for monitoring cancer relapse after surgical resection. Inorganic lanthanide (Ln3+) nanoparticles (NPs), owing to their superior physicochemical characteristics, are regarded as a new generation of luminescent nano-bioprobes in the field of cancer diagnosis and therapy. In this progress report, a focus is set on our recent efforts on the development of inorganic Ln3+-NPs as efficient luminescent nano-bioprobes for the ultrasensitive in vitro biodetection of tumor markers, with an emphasis on the dissolution-enhanced luminescent bioassay (DELBA), an emerging technique recently developed toward practical medical applications.

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.

Ultrasensitive FRET-based DNA sensor using PNA/DNA hybridization

In the diagnosis of genetic diseases, rapid and highly sensitive DNA detection is crucial. Therefore, many strategies for detecting target DNA have been developed, including electrical, optical, and mechanical methods. Herein, a highly sensitive FRET based sensor was developed by using PNA (Peptide Nucleic Acid) probe and QD, in which red color QDs are hybridized with capture probes, reporter probes and target DNAs by EDC-NHS coupling. The hybridized probe with target DNA gives off fluorescent signal due to the energy transfer from QD to Cy5 dye in the reporter probe. Compared to the conventional DNA sensor using DNA probes, the DNA sensor using PNA probes shows higher FRET factor and efficiency due to the higher reactivity between PNA and target DNA. In addition, to elicit the effect of the distance between the donor and the acceptor, we have investigated two types of the reporter probes having Cy5 dyes attached at the different positions of the reporter probes. Results show that the shorter the distance between QDs and Cy5s, the stronger the signal intensity. Furthermore, based on the fluorescence microscopy images using microcapillary chips, the FRET signal is enhanced to be up to 276% times stronger than the signal obtained using the cuvette by the fluorescence spectrometer. These results suggest that the PNA probe system conjugated with QDs can be used as ultrasensitive DNA nanosensors.

Ultrastable and Biofunctionalizable Gold Nanoparticles

Gold nanoparticles provide an excellent platform for biological and material applications due to their unique physical and chemical properties. However, decreased colloidal stability and formation of irreversible aggregates while freeze-drying nanomaterials limit their use in real world applications. Here, we report a new generation of surface ligands based on a combination of short oligo (ethylene glycol) chains and zwitterions capable of providing nonfouling characteristics while maintaining colloidal stability and functionalization capabilities. Additionally, conjugation of these gold nanoparticles with avidin can help the development of a universal toolkit for further functionalization of nanomaterials.

Hydrophobic and Metallophobic Surfaces: Highly Stable Non-wetting Inorganic Surfaces Based on Lanthanum Phosphate Nanorods

Metal oxides, in general, are known to exhibit significant wettability towards water molecules because of the high feasibility of synergetic hydrogen-bonding interactions possible at the solid-water interface. Here we show that the nano sized phosphates of rare earth materials (Rare Earth Phosphates, REPs), LaPO4 in particular, exhibit without any chemical modification, unique combination of intrinsic properties including remarkable hydrophobicity that could be retained even after exposure to extreme temperatures and harsh hydrothermal conditions. Transparent nanocoatings of LaPO4 as well as mixture of other REPs on glass surfaces are shown to display notable hydrophobicity with water contact angle (WCA) value of 120° while sintered and polished monoliths manifested WCA greater than 105°. Significantly, these materials in the form of coatings and monoliths also exhibit complete non-wettability and inertness towards molten metals like Ag, Zn, and Al well above their melting points. These properties, coupled with their excellent chemical and thermal stability, ease of processing, machinability and their versatile photo-physical and emission properties, render LaPO4 and other REP ceramics utility in diverse applications.

A label-free electrochemiluminescence immunosensor based on EuPO4 nanowire for the ultrasensitive detection of Prostate specific antigen

EuPO4 nanowire, which exhibited strong and stable cathodic electrochemiluminescence (ECL) activity, was used for the first time to fabricate an immunosensor for the detection of prostate specific antigen (PSA). EuPO4 has some inherent excellent properties such as long luminescence lifetime, narrow emission band, high quantum yield and low toxicity. Based on these properties, a novel label-free ECL immunosensor was developed using EuPO4 as a sensing matrix. Chitosan solution was used to disperse EuPO4 nanowires and the amino groups on chitosan enabled the covalent attachment of capture antibodies. After the modification of the electrode surface with EuPO4 nanowires, anti-PSA was then immobilized on them, forming a label-free immunosensing interface. The specific binding of PSA on the electrode inhibited the ECL reaction of EuPO4 nanowires with the coreactant due to the steric hindrance effect (Deng et al., 2013). Under the optimum conditions, a good linear relationship between ECL intensity and the logarithm of PSA concentration was obtained in the range of 0.0005-80 ng/mL with a detection limit of 177.33 fg/mL. The proposed ECL immunosensor showed good stability, acceptable selectivity and reproducibility.

Sacrificial conversion of layered rare-earth hydroxide (LRH) nanosheets into (Y1−xEux)PO4 nanophosphors and investigation of photoluminescence

Sacrificial conversion of LRH nanosheets has led to (Y,Eu)PO₄ red-emitting nanophosphors.

Magnetic-downconversion luminescent bifunctional BaGdF5:Dy3+,Eu3+ nanospheres: energy transfer, multicolor luminescence and paramagnetic properties

The color-tunable and white light emissions have been obtained in Dy³⁺ and Eu³⁺ co-activated BaGdF₅ phosphors by adopting different excitation wavelengths. Simultaneously, the obtained samples also exhibit paramagnetic properties at room temperature and low temperature.

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

In this work, water-soluble Yb(3+)/Er(3+) codoped Bi2O3 upconversion (UC) nanospheres with uniform morphology have been successfully synthesized via a solid-state-chemistry thermal decomposition process. With 980 nm near-infrared irradiation, the Bi2O3:Yb(3+)/Er(3+) nanospheres have bright UC luminescence (UCL). Moreover, multicolor UC emissions (from green to red) can be tuned by simply changing the Yb(3+) ions doping concentration. After citric acid molecules were grafted on the surface of Bi2O3:20% Yb(3+)/2% Er(3+) nanospheres, the MTT assay on HeLa cells and CCK-8 assay on osteoblasts show that the UC nanospheres exhibit excellent stability and biocompatibility. The possibility of using these nanoprobes with red UCL for optical imaging in vivo has been demonstrated. Furthermore, Bi(3+) and Yb(3+) containing nanospheres as binary contrast agent also exhibited significant enhancement of contrast efficacy than iodine-based contrast agent via X-ray computed tomography (CT) imaging at different voltage setting (80-140 kVp), indicating they have potential as CT imaging contrast agent. Thus, Yb(3+)/Er(3+) codoped Bi2O3 nanospheres could be used as dual modality probe for optical and CT imagings.

Synthesis, luminescence, and anti-tumor properties of MgSiO3:Eu-DOX-DPP-RGD hollow microspheres

In this report, MgSiO3:Eu-DOX-DPP-RGD hollow microspheres employed for simultaneous imaging and anti-cancer therapy have been designed by sequentially loading the anti-tumor drugs doxorubicin (DOX), light-activated platinum(iv) pro-drug PPD, and a targeted peptide of NH2-Gly-Arg-Gly-Asp-Ser (RGD) onto MgSiO3:Eu mesoporous hollow spheres, which were synthesized using solid SiO2 spheres as sacrificed template by a facile hydrothermal process based on the Kirkendall effect. The photoluminescence intensity of MgSiO3:Eu has been optimized, which can emit a recognized red signal in vitro and in vivo under modest ultraviolet (UV) irradiation. It was found that the platform has high biocompatibility and could become intracellular through fast and effective endocytosis with the aid of the targeted peptide RGD, and chemotherapeutic drugs DOX and light-activated platinum(iv) pro-drug DPP that can be released from the carrier to induce an obvious inhabitation effect to HeLa cancer cells (survival rate of only 17.4%), which has been verified by in vitro and in vivo results. Moreover, the in vitro result using a photosensitizer ZnPc loaded carrier shows that the system is not suitable for ZnPc induced photodynamic therapy. The apparent imaging effect and high anti-tumor efficacy of this functional system give it great potential in actual clinical applications.

One-Step Protein Conjugation to Upconversion Nanoparticles

The emerging upconversion nanoparticles offer a fascinating library of ultrasensitive luminescent probes for a range of biotechnology applications from biomarker discovery to single molecule tracking, early disease diagnosis, deep tissue imaging, and drug delivery and therapies. The effective bioconjugation of inorganic nanoparticles to the molecule-specific proteins, free of agglomeration, nonspecific binding, or biomolecule deactivation, is crucial for molecular recognition of target molecules or cells. The current available protocols require multiple steps which can lead to low probe stability, specificity, and reproducibility. Here we report a simple and rapid protein bioconjugation method based on a one-step ligand exchange using the DNAs as the linker. Our method benefits from the robust DNA-protein conjugates as well as from multiple ions binding capability. Protein can be preconjugated via an amino group at the 3' end of a synthetic DNA molecule, so that the 5' end phosphoric acid group and multiple phosphate oxygen atoms in the phosphodiester bonds are exposed to replace the oleic acid ligands on the surface of upconversion nanoparticles due to their stronger chelating capability to lanthanides. We demonstrated that our method can efficiently pull out the upconversion nanoparticles from organic solvent into an aqueous phase. The upconversion nanoparticles then become hydrophilic, stable, and specific biomolecules recognition. This allows us to successfully functionalize the upconversion nanoparticles with horseradish peroxidise (HRP) for catalytic colorimetric assay and for streptavidin (SA)-biotin immunoassays.

Multimodal cancer imaging using lanthanide-based upconversion nanoparticles

Multimodal nanoprobes that integrate different imaging modalities in one nano-system could offer synergistic effect over any modality alone to satisfy the higher requirements on the efficiency and accuracy for clinical diagnosis and medical research. Upconversion nanoparticles (UCNPs), particularly lanthanide (Ln)-based NPs have been regarded as an ideal building block for constructing multimodal bioprobes due to their fascinating properties. In this review, we first summarize recent advances in the optimizations of existing UCNPs. In particular, we highlight the applications of Ln-based UCNPs for multimodal cancer imaging in vitro and in vivo. The explorations of UCNPs-based multimodal nanoprobes for targeting diagnosis and imaging-guided therapeutics are also presented. Finally, the challenges and perspectives of Ln-based UCNPs in this rapid growing field are discussed.

Synthesis and characterization of lanthanum phosphate nanoparticles as carriers for (223)Ra and (225)Ra for targeted alpha therapy

INTRODUCTION

Targeted alpha therapy (TAT) has the potential for killing micro-metastases with minimum collateral damage to surrounding healthy tissue. In-vivo generator radionuclides, such as(223)Ra, (225)Ra, and (225)Ac, are of special interest for radiotherapeutic applications as they emit multiple α-particles during their decay. Utilizing appropriate carriers capable of retaining both the parent radioisotope as well as daughter products is important for the effective delivery of the radioisotope to the tumor site while mitigating global in vivo radiotoxicity. In this work, LaPO4 core and core+2 shells nanoparticles (NPs) (NPs with 2 layers of cold LaPO4 deposited on the core surfaces) were synthesized containing either (223)Ra or(225)Ra/(225)Ac, and the retention of the parents and daughters within the NPs in vitro was investigated.

METHODS

Core LaPO4 NPs were synthesized in aqueous solution by reacting 1 equivalent of La(NO3)3, along with few microcuries of either (223)Ra or (225)Ra/(225)Ac, with 1 equivalent of sodium tripolyphosphate (TPP) under moderate heating and purified by membrane dialysis. Core-shell NPs were also synthesized with one (core+1 shell) and two (core+2 shells) cold LaPO4 layers deposited onto the radioactive cores. The NPs were then characterized by transmission electron microscopy (TEM) and powder x-ray diffraction (XRD). Identification and quantification of radioactive parents and daughters released from the NPs in vitro were investigated using gamma-ray spectroscopy.

RESULTS

XRD and TEM analysis revealed that the NPs crystallized in the rhabdophane phase with mean diameters of 3.4 and 6.3nm for core and core+2 shells, respectively. The core LaPO4 NPs retained up to 88% of (223)Ra over 35days. However, in the core+2 shells NPs, the retention of (223)Ra and its daughter, (211)Pb, was improved to >99.9% over 27days. Additionally, the retention of (225)Ra/(225)Ac parents was >99.98% and ~80% for the (221)Fr and (213)Bi daughters over 35days for the core+2 shells NPs.

CONCLUSIONS

The in vitro retention of both parents and daughters results suggests that LaPO4 NPs are potentially effective carriers of radium isotopes.