GdPO4 Nanoparticles Research Articles

Tuning the Fe-Gd nanoparticles co-functionalized mesoporous carbon from sphere to nanobowl for advanced bioapplications

Studies on the function-integrated nanocomposites with well-tuned morphologies have received considerable interest. Here, we reported the preparation of mesoporous carbon nanobowl integrated with stoichiometric γ-Fe2O3 and GdPO4 nanoparticles (Fe-Gd/MCN-B) for morphological advantage exploration. Followed by (i) emulsion-induced interface anisotropic assembly of polydopamine, (ii) solvent evaporation-induced sorption of Wells-Dawson-like heterometallic cluster of {Fe6Gd6P6} and (iii) temperature-programmed carbonization, Fe-Gd/MCN-B with the size around 200 nm was isolated. Our in-vitro studies revealed that Fe-Gd/MCN-B showed a 63.0 % amplified photoacoustic (PA) signal intensity as compared with its nanospherical analogue of Fe-Gd/MCN-S owing to the enhanced light harvesting and photothermal conversion on the interface of its nanobowl morphology. Furthermore, the combined magnetic resonance (MR) imagining, drug delivery and photothermal treatment efficacy in Fe-Gd/MCN-B were also validated in-vitro. These results demonstrated that the delicate design of the morphology of function-integrated nanocomposites is an available way for enhanced imaging performance.

Judd‐Ofelt analysis and optical properties of Eu3+‐doped GdPO4 phosphors synthesized by combustion method

AbstractThe Eu3+‐doped GdPO4 nanoparticles were prepared via a straightforward combustion method using urea as fuel and nitrates as a precursor. X‐ray powder diffraction patterns, infrared spectrum (IR), HR‐TEM, photoluminescence (PL), phonon sideband and photoluminescence excitation (PLE) were researched. There is a phase transition from the hexagonal phase into the monoclinic phase when the calcined temperature is over 700 °C. All of phosphors have similar morphology and the average diameters for nanoparticles are 20–30 nm. Under the excitation at 273 nm, GdPO4:Eu3+ powders showed red emission bands originating from the 5D0–7FJ (J = 1, 2, 3 and 4) transitions of Eu3+. The orange‐red emission (5D0–7F1 transition) is dominated because the Eu3+ ions exist with inversion symmetry in the lattice. The study suggests that the optimal Eu3+ ions concentration is 5 mol%. In addition, the second order crystal field parameter (B20) and the influence of concentration of Eu3+ ions on decay time are also mentioned, the intensity parameters (Ω2,4,6) and quantum efficiency were determined based on Judd‐Ofelt theory.

Hydrothermal Synthesis of Well-Defined Red-Emitting Eu-Doped GdPO4 Nanophosphors and Investigation of Their Morphology and Optical Properties

Rare-earth-doped GdPO4 nanoparticles have recently attracted much scientific interest due to the simultaneous optical and magnetic properties of these materials and their possible application in bio-imaging. Herein, we report the hydrothermal synthesis of GdPO4:Eu3+ nanoparticles by varying different synthesis parameters: pH, <Gd>:<P> molar ratio, and Eu3+ concentration. It turned out that the Eu3+ content in the synthesized nanoparticles had little effect on particle shape and morphology. The synthesis media pH, however, has showed a pronounced impact on particle size and distribution, i.e., the nanoparticle length can be adjusted from hundreds to tens of nanometers by changing the pH from 2 to 11, respectively. Increasing the <Gd>:<P> molar ratio resulted in a decrease in nanoparticle length and an increase in its width. The temperature-dependent measurements in the 77–500 K range revealed that the GdPO4:50%Eu3+ sample maintains half of its emission intensity, even at room temperature (TQ1/2 = 291 ± 19 K).

Near White Emitting Host Sensitized Dy3+ doped GdPO4 Nanoparticles: Luminescence Studies

Host sensitized GdPO4 nanoparticles doped with Dy3+ ions have been prepared by co-precipitation method with ethylene glycol as capping agent as well as solvent. The as-prepared samples exhibit crystalline monoclinic phase of GdPO4. From the luminescence study, 4F9/2→6H15/2 of Dy3+ is dominant over 4F9/2→6H13/2 transition indicating the occupation of inversion symmetry by Dy3+ ions in the host lattice. The steady state luminescence shows effective energy transfer from gadolinium (Gd3+) to dysprosium (Dy3+) ions in the doped samples with optimum emission of Dy3+ (2 at.%) doped sample. Decay lifetime values also decrease upon increasing Dy3+ ion concentration on account of cross-relaxation concentration quenching effect. The emission colour of single phase as-prepared Dy3+ doped GdPO4 nanoparticles can be tuned from blue-violet to near white light by changing the excitation wavelength. Tunability of the light and white light emission are supported by Commission Internationale de l’Eclairage (CIE) chromaticity.

Hollow carbon nanospheres embedded with stoichiometric γ-Fe2O3 and GdPO4: tuning the nanospheres for in vitro and in vivo size effect evaluation.

The size modulation of hollow carbon nanospheres (HCSs) has attracted great interest in the contexts of cellular uptake, drug delivery and bioimaging. In this study, a facile fabrication method was specifically used to minimize all influencing factors except for the particle size. A series of nanoparticles of hollow carbon nanospheres embedded with magnetic resonance imaging (MRI) nanoagent γ-Fe2O3 and GdPO4 nanoparticles (Fe–Gd/HCS), were successfully prepared and applied to in vitro/vivo evaluation with well-defined sizes of ∼100 nm (Fe–Gd/HCS-S), ∼200 nm (Fe–Gd/HCS-M), and ∼300 nm (Fe–Gd/HCS-L), respectively. Then the in vitro size effect of Fe–Gd/HCS was systematically investigated by bio-TEM, CLSM, CCK-8 assay, and flow cytometry revealing that Fe–Gd/HCS could be internalized and the cellular uptake amounts increase with the decrease of size. Furthermore, the in vivo size-effect behavior of Fe–Gd/HCS (∼100 nm, ∼200 nm, ∼300 nm) was tracked by MRI technique, demonstrating that all Fe–Gd/HCS can distinguish the liver, in which Fe–Gd/HCS with the smallest particle size exhibited the best performance among these nanoparticles. By leveraging on these features, Fe–Gd/HCS-S (∼100 nm) was further chosen as a theranostic agent, preliminarily presenting its capability for multi-modal imaging and therapy.

Effect of Ce3+ Co-doping on GdPO4:Tb3+ Nanoparticles: Photoluminescence and Energy Transfer Studies

Low temperature synthesis of Tb3+-doped GdPO4 nanoparticles sensitized with Ce3+ (Ce3+ = 0, 3, 5, 7 and 10 at.%) have been reported. Ethylene glycol was used as capping agent as well as reaction medium at 160 ºC. The as-prepared particles crystallized in a monoclinic structure with an average crystallite size of 25-46 nm. From the photoluminescence study, enhanced emission of Tb3+ with co-doping of Ce3+ was attributed to efficient energy transfer from the sensitizer to activator. The luminescence emission intensity increases upto 5 at.% of Ce3+ and then decreases. Less efficient energy transfer from sensitizer to the activator with increasing concentration of sensitizer may be attributed to critical concentration of Ce3+ with the host or dipole-quadrupole interaction amongst the Ce3+ ions. Moreover, presence of -OH group in the samples will make them a potential target for biological labeling and optical devices.

Impacts of anthropogenic gadolinium on the activity of the ammonia oxidizing bacterium Nitrosomonas europaea

Widespread use of gadolinium-based contrast agents in medical imaging has resulted in increased Gd inputs to municipal wastewater treatment plants. Others have reported that typical wastewater treatment does not attenuate Gd, resulting in discharges to natural waters. However, whether elevated Gd impacts the performance of biological treatment has not been investigated. We examined whether gadolinium chloride or Gd chelated with diethylenetriaminepentaacetic acid (DTPA) affected the activity of the model nitrifying bacterium Nitrosomonas europaea. At nominal GdCl3 additions ranging from 1 to 500 μM, no impact was observed compared to the control. Most (>98%) of the added Gd precipitated, and extracellular GdPO4 nanoparticles were observed. When chelated with DTPA, Gd remained soluble, but no statistically significant impact on ammonia oxidation was observed until the highest concentrations tested. At 300 and 500 μM Gd-DTPA, a temporary reduction of nitrite production relative to the control (effect size 1.3 mg l−1 and 1.5 mg l−1, respectively, at 24 h) was seen. By itself, DTPA was highly inhibitory. Modeling suggested that DTPA likely chelated other metals, but adjusting the concentrations of the most abundant metals in the medium, calcium and magnesium, indicated that lowering their free ion activities was probably not the cause of inhibition. Complexation of other essential metals was more likely. Our studies indicate that while the low bioavailability of Gd may limit its ecosystem impacts, the role of synthetic ligands used with Gd and other rare earth elements should be considered as the production, use and disposal of these elements increases.

Photoluminescence properties of gadolinium phosphate nanoprisms doped with lanthanide ions for multicolor live cell imaging

Lanthanide fluorescence nanoprobe is versatile in multicolor cell imaging, although it still faces a great challenge in improving its luminescent efficiency. Herein, we validated the feasibility of lanthanide ions co-doped gadolinium phosphate nanocrystals serving as a safe, effective and color-tunable fluorescence probe for live cell imaging. Well-crystallized hexagonal phase GdPO4 nanoparticles with multi-morphologies such as nanowires, nanorods, tetragonal nanocubes and hexagonal nanoprisms were synthesized via a typical hydrothermal method. We have systematically investigated the synthesis of different morphologies of GdPO4 nanoparticles through adjusting their processing parameters. The nanoparticles can gain a bright color-tunable photoluminescence from red, orange, yellow to green region when the GdPO4 nanoparticles are co-doped with Eu3+ and Tb3+ ions. The Tb3+ doping significantly enhances the characteristic 4f → 4f transitions of Eu3+ owing to a specific cross-relaxation process from Tb3+ to Eu3+ ions; the mechanism underlying the cross relaxation was exposited in detail. Further biological experiments in vitro proved that the prepared nanoprisms could exhibit a favourable biocompatibility with negligible toxicity. The current investigation manifests a high potential of the nanoparticles applicable to fluorescence imaging probe for live cells.

Effect of calcination temperature on phase evolution and photoluminescent properties of GdPO4:Eu3+ nanoparticle phosphors synthesized by combustion method

AbstractEu3+ ‐doped GdPO4 nanoparticles were synthesized by a straightforward combustion method using urea as fuel and metal nitrates as precursors. Structures, morphologies and photoluminescent properties of the synthesized samples were studied by X‐ray diffraction, scanning electron microscopy and photoluminescent spectroscopy. There are two types of crystal structures formed during the annealing process: hexagonal GdPO4.H2O and monoclinic GdPO4. The former can be found at low annealing temperatures (300‐500°C) while the latter can be obtained at higher annealing temperatures (700‐900°C). The average diameters for nanoparticles are 20‐30 nm. Under the excitation at 273 nm, both GdPO4.H2O:Eu3+ and GdPO4:Eu3+ powders showed red emission bands originating from the 5D0 ‐ 7FJ (J = 1, 2, 3 and 4) transitions of Eu3+. Their PL intensity and crystal structures exhibit a similar behavior as a function of the annealing temperature.

Gadolinium phosphate/chitosan scaffolds promote new bone regeneration via Smad/Runx2 pathway

Gadolinium (Gd) is one of trace rare earth elements (REEs) existing in human bones; however, the underlying mechanisms of Gd element on positive cell response and bone regeneration have rarely been reported. Herein, we firstly constructed GdPO4/chitosan (CTS) scaffolds by lyophilisation method. The appropriate macropores and biocompatible chemical components improved the osteoconductivity of the GdPO4/CTS scaffolds, resulting in admired cell spreading and in vivo bone tissue in-growth. The concentrations of the as-released Gd3+ ions were kept in safety ranges, and had non-toxicity to rat bone marrow mesenchymal stem cells (rBMSCs). Notably, the GdPO4 nanoparticles in the GdPO4/CTS scaffolds significantly promoted the osteogenic differentiation of rBMSCs via activated Smad/Runx2 signaling pathway. As compared with β-TCP/CTS scaffolds, the GdPO4/CTS scaffolds remarkably up-regulated the levels of ALP, Runx-2, OCN and Col-I expression. Moreover, rat critical calvarial defect models revealed that the newly formed bone tissues were much greater in the GdPO4/CTS group than in the β-TCP/CTS group. The exciting finding revealed the underlying mechanism of GdPO4 nanoparticles on enhanced osteogenic activity, and provided a promising GdPO4-based scaffold for bone regeneration.

Synthesis, characterization and electrochemical monitoring of drug release properties of dual stimuli responsive mesoporous GdPO4:Eu3+ nanoparticles

The drug loading and release properties of Eu3+ doped GdPO4 nanoparticles (NPs) were studied using a simple electrochemical protocol in an in-vitro environment, taking acetaminophen as a model drug. The electrochemical monitoring of drug release was also validated with absorption spectroscopy technique. For this purpose, dual stimuli (pH and temperature) responsive monoclinic mesoporous GdPO4 nanoparticles of size ∼22 nm were synthesized by a simple hydrothermal method. Crystal structure, size, shape, morphology, porosity, optical property and magnetic properties of the obtained product were studied by different characterization techniques. Successful loading of drug in NPs was investigated by Fourier transform infrared spectroscopy (FT-IR). Photoluminescence (PL) measurement shows orange-red color emission corresponding to 5D0→7F2 transitions of Eu3+ ions. The vibrating sample magnetometer (VSM) measurements showed negligible hysteresis in both samples, suggesting retention of the superparamagnetic behavior of GdPO4 NPs. The high loading capacity of 79% and encapsulation efficiency of 83% is observed when acetaminophen, an anti-fever drug, was loaded on these mesoporous GdPO4 NPs. The drug was attached on NPs surfaces via absorption, without any special surface modification. During drug release studies, a spontaneous and smooth release from these mesoporous NPs was observed at a moderate-high temperature (37 °C) and low pH (pH 5) with no sign of burst release. These nanoparticles were capable of targeting and specific release of the loaded drug in response to pH and temperature and hence may serve as a potential drug carrier for in-vivo applications.

Single Molecular Wells–Dawson‐Like Heterometallic Cluster for the In Situ Functionalization of Ordered Mesoporous Carbon: A T1‐ and T2‐Weighted Dual‐Mode Magnetic Resonance Imaging Agent and Drug Delivery System

Developing a feasible way to prepare highly dispersed heterometallic nanoparticles incorporated in porous carbon composites is of significant importance for multifunctional materials. In this work, heterometallic γ‐Fe2O3 and GdPO4 nanoparticles that are incorporated in ordered mesoporous carbon composites are facilely prepared by a one‐pot in situ method using a Wells–Dawson‐like cluster of [Fe6Gd6(μ3‐O)2(CO3)(O3PPh)6(O2C t Bu)18] ({Fe6Gd6P6} for short) as the precursor. It is verified that the γ‐Fe2O3 and GdPO4 nanoparticles are highly dispersed and embedded into the carbon matrix with a particle size smaller than 5 nm, even when the carbon matrix is changed from 2D hexagonal P6mm to 3D body‐centered cubic Im‐3m symmetry. Additionally, a formation mechanism is proposed. Furthermore, dual‐mode magnetic resonance (MR) imaging and drug carrier properties are evaluated by in vitro experiments, which show a satisfactory T 1‐ and T 2‐weighted MR imaging effect with r 1 and r 2 relaxivity values of 2.7 and 183.7 mM−1 s−1, respectively, and doxorubicin hydrochloride carrier amount of 102 mg g−1, identifying a combined function for potential diagnostic and therapy.

Spectroscopic properties and Judd–Ofelt analysis of Eu3+ doped GdPO4 nanoparticles and nanowires

Eu3+ doped GdPO4 orthophosphates with hexagonal and monoclinic crystal structures were prepared by a solvothermal process at 160°C. Nanoparticles (NPs) and nanowires (NWs) were obtained using a mixture of water and glycerol as solvents. Luminescence properties of 5% Eu3+ doped GdPO4 NPs and NWs were investigated. As-obtained luminescent NWs:Eu and NPs:Eu powders were post-annealed at 750°C since this temperature did not change neither their initial morphology nor their crystalline structure and led to luminescence efficiency intense enough to suit optical applications. A post-heating treatment of the samples at higher temperature (1000°C) resulted in a change in both the crystalline structure from hexagonal to monoclinic form and the morphology. Excitation and emission spectra as well as luminescence decays were recorded on both post-annealed luminescent NW:Eu and NP:Eu powders. A comparative study of the optical results obtained for the different morphologies and structures was carried out by calculating the asymmetry ratio (A21) of Eu3+ from emission spectra. The symmetry of the local environment of Eu3+ activators has been described in the frame of Judd–Ofelt theory, using Ω2 and Ω4 intensity parameters derived from emission spectra data analysis, adopting a standard procedure. It was observed that Ω2 value for the NPs is different from that of the NWs indicating that the environment surrounding the active ion changes depending on the sample morphologies. The radiative lifetimes of the 5D0 excited state and the corresponding branching ratios for different emission transitions were also estimated and compared to the recorded luminescence decay rates at room temperature.

Upconversion Luminescence of Tb3+ and Yb3+ Co-doped Hexagonal and Monoclinic GdPO4 Nanophosphors

Tb3+ and Yb3+ codoped hexagonal GdPO4 nanorods have been prepared by a hydrothermal method at 220°C for 12 h and monoclinic GdPO4 nanoparticles have been obtained by sintering the hydrothermal products at 900°C for 5 h. Green upconversion luminescence of Tb3+ has been observed when pumped by 980 nm diodes due to efficiently cooperative energy transfer from codopant Yb3+. The luminescence of Tb3+ in both hexagonal and monoclinic GdPO4 nanophosphors has been comparatively studied. The dependence of the upconversion luminescence intensity on pump laser power shows that two-phonon processes involved in upconversion luminescence of the emission level 5D4 of Tb3+ is populated via two-photon process. Upconversion luminescence emission intensity and the energy transfer efficiency ηT from Yb3+ to Tb3+ ions upon the concentration of Tb3+ have been investigated.

Liquid Phase Synthesis and Characterization of LaPO4:Yb3+/GdPO4 Nanoparticles with NIR Emission under NIR Excitation

not Available.

Preparation of Yb3+ doped GdPO4 nanoparticles by solution-based processing

Yb3+ doped GdPO4 (GdPO4:Yb3+) nanoparticles are prepared in glycol solvent by autoclave treatment at 230 °C for 120 min. According to X-ray diffraction (XRD) patterns, the sample prepared in ethylene glycol is monazite-type GdPO4:Yb3+ without crystal water, while the sample prepared in 1,4-butanediol is rhabdophane-type GdPO4:Yb3+ with crystal water. The former shows more intense near infrared photoluminescence due to the f-f transition of Yb3+ in comparison with the latter. These results indicate that quenching of Yb3+ emission is attributed to energy dissipation due to the O-H vibration of crystal water. When the samples are prepared in ethylene glycol by autoclave treatment at 230 °C for different aging time, the crystallization degree estimated from integrated intensities of XRD peaks increases with increasing aging time. At the same time, the Yb3+ emission becomes strong. We found out that the photoluminescence intensity is linearly related with the crystallization degree.

Fabrication of a silica sphere with fluorescent and MR contrasting GdPO4 nanoparticles from layered gadolinium hydroxide

The delaminated gadolinium hydroxide layers doped with Eu(3+) ions were assembled on the surface of silica spheres and annealed at high temperatures, resulting in the formation of fluorescent and MR active GdPO(4) : Eu nanoparticles at the surface.