Effect of Neodymium Doping on MRI Relaxivity of Gadolinium Oxide Nanoparticles

Background

Gadolinium oxide nanoparticles as positive contrast material of magnetic resonance imaging (MRI) have attracted a great attention due to the appropriate magnetic properties. One of the most desirable features of these nanoparticles is their ability of doping with other lanthanides which can change their properties.

Objective

This study aimed to investigate the effect of neodymium doping on MRI relaxivity of the gadolinium oxide nanoparticles.

Material and Methods

In this experimental study, the oleic acid coated gadolinium oxide nanoparticles and the neodymium doped nanoparticles were prepared by polymer pyrolysis method. X-ray diffraction test and scanning electron microscopy were used for characterization of the particles. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to investigate the in vitro cell toxicity of the nanoparticles. The r1 and r2 relaxivities were extracted from the T1 and T2 weighted MR images, respectively.

Results

The average size of the cytocompatible spherical-like shape nanoparticles was 40 nm. The neodymium doped nanoparticles produced a significant decrease in the r1 relaxivity, and a 1.7 fold increase in the r2 relaxivity compared to the gadolinium oxide nanoparticles.

Conclusion

Doping of neodymium into the gadolinium oxide nanoparticles suppresses the r1 relaxivity and enhances the r2 relaxivity of the nanoparticles.

In vivo immunotoxicity of Gd2 O3 :Eu3+ nanoparticles and the associated molecular mechanism

The in vivo toxicity of Gd₂ O₃ :Eu³⁺ nanoparticles (NPs) used as dual-modal nanoprobes for molecular imaging has not been studied, and the corresponding molecular mechanism of immunotoxicity remains unknown. In this study, we investigated the cytotoxicity, in vitro apoptosis, and in vivo immunotoxicity of Gd₂ O₃ :Eu³⁺ NPs. The NPs showed little immunotoxicity to BALB/c mice. We explored the possible role of the phosphoinositide 3-kinase (PI3K) signaling pathway and found that reactive oxygen species could act as secondary messengers in cellular signaling, inhibiting PI3K expression in the liver. The immune suppression caused by PI3K inhibition helped the mice adapt to stress. The immunotoxicities caused by Gd₂ O₃ :Eu³⁺ and gadodiamide, a commonly used contrast agent, were not significantly different, and the mice were able to tolerate the immunotoxicity caused Gd₂ O₃ :Eu³⁺ NPs in vitro and in vivo experiments. The results suggest that Gd₂ O₃ :Eu³⁺ NPs are sufficiently biocompatible to be used safely in preclinical applications and show promise as bio-imaging agents. Moreover, the in vivo molecular mechanism of immunotoxicity caused by the Gd₂ O₃ :Eu³⁺ NPs provides a platform for further research on the immunotoxicity of nano-sized biomaterials.

Gadolinium-based bimodal probes to enhance T1-Weighted magnetic resonance/optical imaging

Gd³⁺-based contrast agents have been extensively used for signal enhancement of T₁-weighted magnetic resonance imaging (MRI) due to the large magnetic moment and long electron spin relaxation time of the paramagnetic Gd³⁺ ion. The key requisites for the development of Gd³⁺-based contrast agents are their relaxivities and stabilities which can be achieved by chemical modifications. These modifications include coordinating Gd³⁺ with a chelator such as diethylenetriamine pentaacetic acid (DTPA) or 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), encapsulating Gd³⁺ in nanoparticles, conjugation to biomacromolecules such as polymer micelles and liposomes, or non-covalent binding to plasma proteins. In order to have a coherent diagnostic and therapeutic approach and to understand diseases better, the combination of MRI and optical imaging (OI) techniques into one technique entity has been developed to overcome the conventional boundaries of either imaging modality used alone through bringing the excellent spatial resolution of MRI and high sensitivity of OI into full play. Novel MRI and OI bimodal probes have been extensively studied in this regard. This review is an attempt to shed some light on the bimodal imaging probes by summarizing all recent noteworthy publications involving Gd³⁺ containing MR-optical imaging probes. The several key elements such as novel synthetic strategy, high sensitivity, biocompatibility, and targeting of the probes are highlighted in the review. STATEMENT OF SIGNIFICANCE: The present article aims at giving an overview of the existing bimodal MRI and OI imaging probes. The review structured as a series of examples of paramagnetic Gd³⁺ ions, either as ions in the crystalline structure of inorganic materials or chelates for contrast enhancement in MRI, while they are used as optical imaging probes in different modes. The comprehensive review focusing on the synthetic strategies, characterizations and properties of these bimodal imaging probes will be helpful in a way to prepare related work.

Doping nanoparticles using pulsed laser ablation in a liquid containing the doping agent

While doping of semiconductors or oxides is crucial for numerous technological applications, its control remains difficult especially when the material is reduced down to the nanometric scale. In this paper, we show that pulsed laser ablation of an undoped solid target in an aqueous solution containing activator ions offers a new way to synthesise doped-nanoparticles. The doping efficiency is evaluated for laser ablation of an undoped Gd₂O₃ target in aqueous solutions of EuCl₃ with molar concentration from 10^-5 mol L^-1 to 10^-3 mol L^-1. Thanks to luminescence experiments, we show that the europium ions penetrate the core of the synthesised monoclinic Gd₂O₃ nanoparticles. We also show that the concentration of the activators in the nanoparticles is proportional to the initial concentration in europium ions in the aqueous solution, and a doping of about 1% ([Eu]/[Gd] atomic ratio) is reached. On the one hand, this work could open new ways for the synthesis of doped nanomaterials. On the other hand, it also raises the question of undesired penetration of impurities in laser-generated nanoparticles in liquids.

1H NMR Relaxometric Analysis of Paramagnetic Gd2O3:Yb Nanoparticles Functionalized with Citrate Groups

Gd2O3 nanoparticles doped with different amount of Yb3+ ions and coated with citrate molecules were prepared by a cheap and fast co-precipitation procedure and proposed as potential “positive” contrast agents in magnetic resonance imaging. The citrate was used to improve the aqueous suspension, limiting particles precipitation. The relaxometric properties of the samples were studied in aqueous solution as a function of the magnetic field strength in order to evaluate the interaction of the paramagnetic ions exposed on the surface with the water molecules in proximity. The nanoparticles showed high relaxivity values at a high magnetic field with respect to the clinically used Gd3+-chelates and comparable to those of similar nanosytems. Special attention was also addressed to the investigation of the chemical stability of the nanoparticles in biological fluid (reconstructed human serum) and in the presence of a chelating agent.

Wear Resistance Mechanism of Alumina Ceramics Containing Gd₂O₃

Excellent wear resistance of alumina ceramics is a desirable quality for many products. The purpose of this work was to improve the wear resistance of 99% alumina ceramics in an Al₂O₃⁻Gd₂O₃⁻SiO₂⁻CaO⁻MgO (AGSCM) system. The content of Gd₂O₃ varied from 0.01% to 1%. A test of wear rate was performed in a ball milling apparatus in a water environment according to the Chinese industry standard. The compositions and microstructure of this material, as well as the effect of bulk density on wear rate, were studied. The effect of Gd₂O₃ on phases, grain growth mode, and grain boundary cohesion was investigated. It was found that Gd₂O₃ could refine grain size, form compressive stress of the grain boundary, and promote the crystallization of CaAl12O19. The wear rate of this material was as low as 0.00052‰ (the Chinese industry standard wear rate is ≤0.15‰). The mechanisms for wear resistance of AGSCM ceramics were also determined.

Effect of Eu doping concentration on fluorescence and magnetic resonance imaging properties of Gd2O3:Eu3+ nanoparticles used as dual-modal contrast agent

Europium-doped gadolinium oxide (Gd₂O₃:Eu³⁺) nanoparticles (NPs) with favorable properties for use in fluorescence imaging (FI) and magnetic resonance imaging (MRI) dual-modal contrast agent has attracted intense attention in biomedical applications. However, limited information is available on balancing FI and MRI by adjusting doping concentrations. In this study, Gd₂O₃:Eu³⁺ NPs with various Eu³⁺ doping concentrations were prepared by the facile and general technique of laser ablation in liquid (LAL). The influence of Eu³⁺-doping concentration on fluorescence properties and longitudinal relaxivity were investigated. The optimum Eu³⁺-doping concentration with both high fluorescence properties and longitudinal relaxivity was determined to be 5%. The characterization of the structure, morphology, and composition shows that these NPs possess good crystallinity and excellent dispersibility. These results show that Gd₂O₃:Eu³⁺ NPs prepared by LAL are promising candidates for highly efficient FI and MRI dual-modal contrast agents.

Microemulsion-made gadolinium carbonate hollow nanospheres showing magnetothermal heating and drug release

Gadolinium carbonate (Gd₂(CO₃)₃) hollow nanospheres and their suitability for drug transport and magnetothermally-induced drug release are presented. The hollow nanospheres are prepared via a microemulsion-based synthesis using tris(tetramethylcyclopentadienyl)gadolinium(iii) and CO₂ as the starting materials. Size, structure and composition of the as-prepared Gd₂(CO₃)₃ hollow nanospheres are comprehensively validated by several independent analytical methods (HRTEM, HAADF-STEM, DLS, EDXS, XRD, FT-IR, DTA-TG). Accordingly, they exhibit an outer diameter of 26 ± 4 nm, an inner cavity of 7 ± 2 nm, and a wall thickness of 9 ± 3 nm. As a conceptual study, the nanocontainer-functionality of the Gd₂(CO₃)₃ hollow nanospheres is validated upon filling with the anti-cancerogenic agent doxorubicin (DOX), which is straightforward via the microemulsion (ME) strategy. The resulting DOX@Gd₂(CO₃)₃ nanocontainers provide the option of multimodal imaging including optical and magnetic resonance imaging (OI, MRI) as well as magnetothermal heating and drug release. As a proof-of-concept, we could already prove the intrinsic DOX-based fluorescence, a low systemic toxicity according to in vitro studies as well as the magnetothermal effect and a magnetothermally-induced DOX release. In particular, the latter is new for Gd-containing nanoparticles and highly promising in view of theranostic nanocontainers and synergistic physical and chemical tumor treatment.

Magnetofluorescent Carbon Dots Derived from Crab Shell for Targeted Dual-Modality Bioimaging and Drug Delivery

We propose a one-pot microwave-assisted pyrolysis method for fabrication of magnetofluorescent carbon quantum dots (MFCQDs), using a combination of waste crab shell and three different transition-metal ions, Gd³⁺, Mn²⁺, and Eu³⁺, referred to as Gd@CQDs, Mn@CQDs, and Eu@CQDs, respectively. Chitin from waste crab shell acted not only as a carbon source but also as a chelating ligand to form complexes with transition-metal ions. Gd@CQDs exhibited a high r₁ relaxivity of 4.78 mM^-1·s^-1 and a low r₂/r₁ ratio of 1.33, suggesting that they show excellent potential as a T₁ contrast agent. Mn@CQDs and Eu@CQDs showed high r₂ relaxivity values of 140.7 and 28.32 mM^-1·s^-1, respectively, suggesting their potential for use as T₂ contrast agents. Further conjugation of Gd@CQDs with folic acid (FA) enabled specific targeting to folate receptor-positive HeLa cells, as confirmed via in vitro magnetic resonance and fluorescence imaging. Doxorubicin (DOX) was selected as a model drug for conjugation with FA-Gd@CQDs. The as-prepared nanocomposites showed significantly higher cytotoxicity toward HeLa cells than free DOX. No apparent cytotoxicity was observed in vivo (zebrafish embryos) or in vitro (cell viability), suggesting that MFCQDs show potential for development as diagnostic probes or theranostic agents.

Gadolinium-based nanoscale MRI contrast agents for tumor imaging

Gadolinium-based nanoscale magnetic resonance imaging (MRI) contrast agents (CAs) have gained significant momentum as a promising nanoplatform for detecting tumor tissue in medical diagnosis, due to their favorable capability of enhancing the longitudinal relaxivity (r₁) of individual gadolinium ions, delivering to the region of interest a large number of gadolinium ions, and incorporating different functionalities. This mini-review highlights the latest developments and applications, and simultaneously gives some perspectives for their future development.

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials, thereby enabling the fabrication of bioconjugates and heterogeneous catalysts. Accurate size control of LSPC-synthesized materials ranging from quantum dots to submicrometer spheres and recent upscaling advancement toward the multiple-gram scale are helpful for extending the applicability of LSPC-synthesized nanomaterials to various fields. By discussing key reports on both the fundamentals and the applications related to laser ablation, fragmentation, and melting in liquids, this Article presents a timely and critical review of this emerging topic.

Structure and dysprosium dopant engineering of gadolinium oxide nanoparticles for enhanced dual-modal magnetic resonance and fluorescence imaging

We report a novel multi-functional nanoarchitecture of Gd₂O₃:Dy³⁺ shell on silica core that enables unique multi-color living cell imaging and remarkable in vivo magnetic resonance imaging.

Gd(OH)3 with multiform morphologies and MRI contrast agent properties by different solvents

The morphology of Gd(OH)₃ is changed from nanorods to microrods, nanoparticles and nanoplates by different solvents, which affects the MRI signal intensity.

Hollow-structured upconverting sesquioxide targeted nanoprobes for magnetic resonance and fluorescence combined imaging

The designed hollow-structured Gd₂O₃ : RE³⁺/Yb³⁺ (RE = Er, Ho, Tm) nanoprobe exhibits highly efficient upconverting fluorescence and MR relaxation properties.

A broad spectrum photon responsive, paramagnetic β-NaGdF4:Yb3+,Er3+ – mesoporous anatase titania nanocomposite

Herein, we report a novel single multifunctional platform based on broad-spectrum photoactive β-NaGdF₄:18% Yb³⁺, 2% Er³⁺ and mesoporous anatase TiO₂ for enhanced energy and simultaneous biomedical applications.

Anaerobic vs. aerobic preparation of silicon nanoparticles by stirred media milling. The effects of dioxygen, milling solvent, and milling time on particle size, surface area, crystallinity, surface/near-surface composition, and reactivity

Silicon nanoparticles milled anaerobically in heptane or mesitylene are smaller and much more reactive than SiNPs milled aerobically in the same solvents for equal attritor milling times.

Layered Seed-Growth of AgGe Football-like Microspheres via Precursor-Free Picosecond Laser Synthesis in Water

Hybrid particles are of great significance in terms of their adjustable optical, electronic, magnetic, thermal and mechanical properties. As a novel technique, laser ablation in liquids (LAL) is famous for its precursor-free, "clean" synthesis of hybrid particles with various materials. Till now, almost all the LAL-generated particles originate from the nucleation-growth mechanism. Seed-growth of particles similar to chemical methods seems difficult to be achieved by LAL. Here, we not only present novel patch-joint football-like AgGe microspheres with a diameter in the range of 1 ~ 7 μm achievable by laser ablation in distilled water but also find direct evidences of their layered seed growth mechanism. Many critical factors contribute to the formation of AgGe microspheres: fast laser-generated plasma process provide an excellent condition for generating large amount of Ge and Ag ions/atoms, their initial nucleation and galvanic replacement reaction, while cavitation bubble confinement plays an important role for the increase of AgGe nuclei and subsequent layered growth in water after bubble collapse. Driven by work function difference, Ge acts as nucleation agent for silver during alloy formation. This new seed-growth mechanism for LAL technique opens new opportunities to develop a large variety of novel hybrid materials with controllable properties.

Phonon-assisted energy back transfer-induced multicolor upconversion emission of Gd2O3:Yb3+/Er3+ nanoparticles under near-infrared excitation

By harnessing the phonon-assisted energy back transfer (EBT) from Er³⁺ to nearby Yb³⁺ ions, we obtain continuous multicolor (from green to red) UC fluorescence in the Gd₂O₃:Yb³⁺/Er³⁺ UCNPs.