Gadolinium oxide nanoplates with high longitudinal relaxivity for magnetic resonance imaging

Kilogram-Scale Synthesis of Extremely Small Gadolinium Oxide Nanoparticles as a T1-Weighted Contrast Agent for Magnetic Resonance Imaging

Magnetic resonance imaging contrast agents are frequently used in clinics to enhance the contrast between diseased and normal tissues. The previously reported poly(acrylic acid) stabilized exceedingly small gadolinium oxide nanoparticles (ES-GdON-PAA) overcame the problems of commercial Gd chelates, but limitations still exist, i.e., high r2/r1 ratio, long blood circulation half-life, and no data for large scale synthesis and formulation optimization. In this study, polymaleic acid (PMA) is found to be an ideal stabilizer to synthesize ES-GdONs. Compared with ES-GdON-PAA, the PMA-stabilized ES-GdON (ES-GdON-PMA) has a lower r2/r1 ratio (2.05, 7.0 T) and a lower blood circulation half-life (37.51 min). The optimized ES-GdON-PMA-9 has an exceedingly small particle size (2.1 nm), excellent water dispersibility, and stability. A facile, efficient, and environmental friendly synthetic method is developed for large-scale synthesis of the ES-GdONs-PMA. The weight of the optimized freeze-dried ES-GdON-PMA-26 synthesized in a 20 L of reactor reaches the kilogram level. The formulation optimization is also finished, and the concentrated ES-GdON-PMA-26 formulation (CGd = 100 mm) after high-pressure steam sterilization possesses eligible physicochemical properties (i.e., pH value, osmolality, viscosity, and density) for investigational new drug application.

Hybrid Polyelectrolyte Capsules Loaded with Gadolinium-Doped Cerium Oxide Nanoparticles as a Biocompatible MRI Agent for Theranostic Applications

Layer-by-layer (LbL) self-assembled polyelectrolyte capsules have demonstrated their unique advantages and capability in drug delivery applications. These ordered micro/nanostructures are also promising candidates as imaging contrast agents for diagnostic and theranostic applications. Magnetic resonance imaging (MRI), one of the most powerful clinical imaging modalities, is moving forward to the molecular imaging field and requires advanced imaging probes. This paper reports on a new design of MRI-visible LbL capsules, loaded with redox-active gadolinium-doped cerium oxide nanoparticles (CeGdO2-x NPs). CeGdO2-x NPs possess an ultrasmall size, high colloidal stability, and pronounced antioxidant properties. A comprehensive analysis of LbL capsules by TEM, SEM, LCSM, and EDX techniques was carried out. The research demonstrated a high level of biocompatibility and cellular uptake efficiency of CeGdO2-x-loaded capsules by cancer (human osteosarcoma and adenocarcinoma) cells and normal (human mesenchymal stem) cells. The LbL-based delivery platform can also be used for other imaging modalities and theranostic applications.

Revisiting the factors influencing the magnetic resonance contrast of Gd2O3 nanoparticles

Gadolinium oxide nanoparticles (GONs) have the potential to be one of the best candidates for the contrast agents of magnetic resonance imaging. Even though the influence of parameters on the relaxation has been substantially demonstrated, the variation of the r ₁ of GONs with a similar structure and surface chemistry implied our limited understanding. We herein synthesized GONs with adjustable size, shape, and crystallinity, modified them with a series of molecules with different acidities, and recorded their r ₁ values and imaging contrast. Our results showed that the isoelectric point could be regarded as an indicator of the relaxation covering the influence of both surface modification and size, which highlighted the impact of protons dissociated from the contrast agents. We further showed that the nanoparticles with lower crystallinity possess higher relaxivity, and this phenomenon manifested significantly under a low field. Our work clarified that the longitudinal relaxivity of Gd₂O₃ nanoparticles is sensitively dependent on the numbers of H⁺ generated from the surface and in the environment, which may shed light on developing high-performance nanoparticulate T ₁ contrast agents.

Functionalized Lanthanide Oxide Nanoparticles for Tumor Targeting, Medical Imaging, and Therapy

Recent progress in functionalized lanthanide oxide (Ln2O3) nanoparticles for tumor targeting, medical imaging, and therapy is reviewed. Among the medical imaging techniques, magnetic resonance imaging (MRI) is an important noninvasive imaging tool for tumor diagnosis due to its high spatial resolution and excellent imaging contrast, especially when contrast agents are used. However, commercially available low-molecular-weight MRI contrast agents exhibit several shortcomings, such as nonspecificity for the tissue of interest and rapid excretion in vivo. Recently, nanoparticle-based MRI contrast agents have become a hot research topic in biomedical imaging due to their high performance, easy surface functionalization, and low toxicity. Among them, functionalized Ln2O3 nanoparticles are applicable as MRI contrast agents for tumor-targeting and nontumor-targeting imaging and image-guided tumor therapy. Primarily, Gd2O3 nanoparticles have been intensively investigated as tumor-targeting T1 MRI contrast agents. T2 MRI is also possible due to the appreciable paramagnetic moments of Ln2O3 nanoparticles (Ln = Dy, Ho, and Tb) at room temperature arising from the nonzero orbital motion of 4f electrons. In addition, Ln2O3 nanoparticles are eligible as X-ray computed tomography contrast agents because of their high X-ray attenuation power. Since nanoparticle toxicity is of great concern, recent toxicity studies on Ln2O3 nanoparticles are also discussed.

Magnetic Nanoparticles in Biology and Medicine: Past, Present, and Future Trends

The use of magnetism in medicine has changed dramatically since its first application by the ancient Greeks in 624 BC. Now, by leveraging magnetic nanoparticles, investigators have developed a range of modern applications that use external magnetic fields to manipulate biological systems. Drug delivery systems that incorporate these particles can target therapeutics to specific tissues without the need for biological or chemical cues. Once precisely located within an organism, magnetic nanoparticles can be heated by oscillating magnetic fields, which results in localized inductive heating that can be used for thermal ablation or more subtle cellular manipulation. Biological imaging can also be improved using magnetic nanoparticles as contrast agents; several types of iron oxide nanoparticles are US Food and Drug Administration (FDA)-approved for use in magnetic resonance imaging (MRI) as contrast agents that can improve image resolution and information content. New imaging modalities, such as magnetic particle imaging (MPI), directly detect magnetic nanoparticles within organisms, allowing for background-free imaging of magnetic particle transport and collection. "Lab-on-a-chip" technology benefits from the increased control that magnetic nanoparticles provide over separation, leading to improved cellular separation. Magnetic separation is also becoming important in next-generation immunoassays, in which particles are used to both increase sensitivity and enable multiple analyte detection. More recently, the ability to manipulate material motion with external fields has been applied in magnetically actuated soft robotics that are designed for biomedical interventions. In this review article, the origins of these various areas are introduced, followed by a discussion of current clinical applications, as well as emerging trends in the study and application of these materials.

2D Gadolinium Oxide Nanoplates as T1 Magnetic Resonance Imaging Contrast Agents

Millions of people a year receive magnetic resonance imaging (MRI) contrast agents for the diagnosis of conditions as diverse as fatty liver disease and cancer. Gadolinium chelates, which provide preferred T₁ contrast, are the current standard but face an uncertain future due to increasing concerns about their nephrogenic toxicity as well as poor performance in high-field MRI scanners. Gadolinium-containing nanocrystals are interesting alternatives as they bypass the kidneys and can offer the possibility of both intracellular accumulation and active targeting. Nanocrystal contrast performance is notably limited, however, as their organic coatings block water from close interactions with surface Gadoliniums. Here, these steric barriers to water exchange are minimized through shape engineering of plate-like nanocrystals that possess accessible Gadoliniums at their edges. Sulfonated surface polymers promote second-sphere relaxation processes that contribute remarkable contrast even at the highest fields (r₁ = 32.6 × 10^-3 m Gd^-1 s^-1 at 9.4 T). These noncytotoxic materials release no detectable free Gadolinium even under mild acidic conditions. They preferentially accumulate in the liver of mice with a circulation half-life 50% longer than commercial agents. These features allow these T₁ MRI contrast agents to be applied for the first time to the ex vivo detection of nonalcoholic fatty liver disease in mice.

Hydrophilic Biocompatible Poly(Acrylic Acid-co-Maleic Acid) Polymer as a Surface-Coating Ligand of Ultrasmall Gd2O3 Nanoparticles to Obtain a High r1 Value and T1 MR Images

The water proton spin relaxivity, colloidal stability, and biocompatibility of nanoparticle-based magnetic resonance imaging (MRI) contrast agents depend on the surface-coating ligands. Here, poly(acrylic acid-co-maleic acid) (PAAMA) (Mw = ~3000 amu) is explored as a surface-coating ligand of ultrasmall gadolinium oxide (Gd2O3) nanoparticles. Owing to the numerous carboxylic groups in PAAMA, which allow its strong conjugation with the nanoparticle surfaces and the attraction of abundant water molecules to the nanoparticles, the synthesized PAAMA-coated ultrasmall Gd2O3 nanoparticles (davg = 1.8 nm and aavg = 9.0 nm) exhibit excellent colloidal stability, extremely low cellular toxicity, and a high longitudinal water proton spin relaxivity (r1) of 40.6 s-1mM-1 (r2/r1 = 1.56, where r2 = transverse water proton spin relaxivity), which is approximately 10 times higher than those of commercial molecular contrast agents. The effectiveness of PAAMA-coated ultrasmall Gd2O3 nanoparticles as a T1 MRI contrast agent is confirmed by the high positive contrast enhancements of the in vivo T1 MR images at the 3.0 T MR field.

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.

Oxygen Vacancy Defect-Induced Activity Enhancement of Gd Doping Magnetic Nanocluster for Oxygen Supplying Cancer Theranostics

This work finds that Fe₃O₄ nanoclusters can rearrange by Gd doping and then self-assemble to a hollow magnetic nanocluster (HMNC), providing larger magnetic moments to obtain an excellent MRI capability and increasing the number of oxygen vacancies in HMNC. The hollow structure makes platinum(IV) prodrugs effectively load into HMNC. Second, plenty of oxygen vacancy defects can capture oxygen molecules, enhance the catalytic activity of HMNC, and then promote intracellular ROS generation. On the basis of this, a targeting iRGD-labeled HMNC nanosystem (iHMNCPt-O₂) is developed through loading oxygen molecules and platinum(IV) prodrugs for chemo- and chemodynamic therapy of cancer. This nanosystem shows an excellent response ability to weak acid and GSH, which can cause a series of cascade reactions in a cell. These cascade reactions are dramatically enhanced at the intracellular ROS level, cause mitochondria and DNA damage, and then induce cancer cell death. Besides, systemic delivery of iHMNCPt-O₂ significantly enhanced the MRI contrast signal of tumors and improved the quality of MR images, accurately diagnosing tumors. Therefore, this work provides a novel method for accelerating the Fenton-like reaction and enhancing the MRI capability and fabricates a promising "all-in-one" system to overwhelm the problems of cancer theranostic.

[T1-weighted magnetic resonance imaging contrast agents and their theranostic nanoprobes]

Magnetic resonance imaging (MRI) is an important imaging modality for clinical disease diagnosis, and nearly 50% of clinical MRI examinations require contrast agents to enhance the diagnostic sensitivity. This review provides a summary of the major MRI contrast agents and their classification, and the advantages and limits of the commercially available MRI contrast agents, and elaborates on the exceedingly small magnetic iron oxide nanoparticles (ES-MIONs), dotted core-shell iron and gadolinium hybrid nanoparticles (FeGd-HN) and exceedingly small gadolinium oxide nanoparticles (ES-GON). These nanoparticles can greatly improve the efficiency of T₁-weighted MRI due to their high r₁ value and low r₂/r₁ ratio, and are expected to be translated into clinical contrast agents for T₁-weighted MRI. The authors also review the diagnostic and therapeutic integration system that combines MRI contrast agents with various tumor therapies, such as MRI-guided ferroptosis therapy, radiosensitization therapy, and photothermal therapy, which allow efficient treatment as well as real-time monitoring of tumors and serve as potential cancer therapy strategies. The possible future research directions in the field of MRI-based multifunctional diagnostic and therapeutic formulations are also discussed.

In Vivo Positive Magnetic Resonance Imaging Applications of Poly(methyl vinyl ether-alt-maleic acid)-coated Ultra-small Paramagnetic Gadolinium Oxide Nanoparticles

The study of ultra-small paramagnetic gadolinium oxide (Gd2O3) nanoparticles (NPs) as in vivo positive (T1) magnetic resonance imaging (MRI) contrast agents is one of the most attractive fields in nanomedicine. The performance of the Gd2O3 NP imaging agents depends on the surface-coating materials. In this study, poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) was used as a surface-coating polymer. The PMVEMA-coated paramagnetic ultra-small Gd2O3 NPs with an average particle diameter of 1.9 nm were synthesized using the one-pot polyol method. They exhibited excellent colloidal stability in water and good biocompatibility. They also showed a very high longitudinal water proton spin relaxivity (r1) value of 36.2 s-1mM-1 (r2/r1 = 2.0; r2 = transverse water proton spin relaxivity) under a 3.0 tesla MR field which is approximately 10 times higher than the r1 values of commercial molecular contrast agents. High positive contrast enhancements were observed in in vivo T1 MR images after intravenous administration of the NP solution sample, demonstrating its potential as a T1 MRI contrast agent.

Exceedingly Small Gadolinium Oxide Nanoparticles with Remarkable Relaxivities for Magnetic Resonance Imaging of Tumors

Gd chelates have occupied most of the market of magnetic resonance imaging (MRI) contrast agents for decades. However, there have been some problems (nephrotoxicity, non-specificity, and low r₁ ) that limit their applications. Herein, a wet-chemical method is proposed for facile synthesis of poly(acrylic acid) (PAA) stabilized exceedingly small gadolinium oxide nanoparticles (ES-GON-PAA) with an excellent water dispersibility and a size smaller than 2.0 nm, which is a powerful T₁ -weighted MRI contrast agent for diagnosis of diseases due to its remarkable relaxivities (r₁ = 70.2 ± 1.8 mM^-1 s^-1 , and r₂ /r₁ = 1.02 ± 0.03, at 1.5 T). The r₁ is much higher and the r₂ /r₁ is lower than that of the commercial Gd chelates and reported gadolinium oxide nanoparticles (GONs). Further ES-GON-PAA is developed with conjugation of RGD2 (RGD dimer) (i.e., ES-GON-PAA@RGD2) for T₁ -weighted MRI of tumors that overexpress RGD receptors (i.e., integrin α_v β₃ ). The maximum signal enhancement (ΔSNR) for T₁ -weighted MRI of tumors reaches up to 372 ± 56% at 2 h post-injection of ES-GON-PAA@RGD2, which is much higher than commercial Gd-chelates (<80%). Due to the high biocompatibility and high tumor accumulation, ES-GON-PAA@RGD2 with remarkable relaxivities is a promising and powerful T₁ -weighted MRI contrast agent.

Cubic versus hexagonal - effect of host crystallinity on the T1 shortening behaviour of NaGdF4 nanoparticles

Sodium gadolinium fluoride (NaGdF4) nanoparticles are promising candidates as T1 shortening magnetic resonance imaging (MRI) contrast agents due to the paramagnetic properties of the Gd3+ ion. Effects of size and surface modification of these nanoparticles on proton relaxation times have been widely studied. However, to date, there has been no report on how T1 relaxivity (r1) is affected by the different polymorphs in which NaGdF4 crystallizes: cubic (α) and hexagonal (β). Here, a microwave-assisted thermal decomposition method was developed that grants selective access to NaGdF4 nanoparticles of either phase in the same size range, allowing the influence of host crystallinity on r1 to be investigated. It was found that at 3 T cubic NaGdF4 nanoparticles exhibit larger r1 values than their hexagonal analogues. This result was interpreted based on Solomon-Bloembergen-Morgan theory, suggesting that the inner sphere contribution to r1 is more pronounced for cubic NaGdF4 nanoparticles as compared to their hexagonal counterparts. This holds true irrespective of the chosen surface modification, i.e. small citrate groups or longer chain poly(acrylic acid). Key aspects were found to be a polymorph-induced larger hydrodynamic diameter and the higher magnetization possessed by cubic nanoparticles.

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.

Structure-Relaxivity Relationships of Magnetic Nanoparticles for Magnetic Resonance Imaging

Magnetic nanoparticles (MNPs) have been extensively explored as magnetic resonance imaging (MRI) contrast agents. With the increasing complexity in the structure of modern MNPs, the classical Solomon-Bloembergen-Morgan and the outer-sphere quantum mechanical theories established on simplistic models have encountered limitations for defining the emergent phenomena of relaxation enhancement in MRI. Recent progress in probing MRI relaxivity of MNPs based on structural features at the molecular and atomic scales is reviewed, namely, the structure-relaxivity relationships, including size, shape, crystal structure, surface modification, and assembled structure. A special emphasis is placed on bridging the gaps between classical simplistic models and modern MNPs with elegant structural complexity. In the pursuit of novel MRI contrast agents, it is hoped that this review will spur the critical thinking for design and engineering of novel MNPs for MRI applications across a broad spectrum of research fields.

GdPO4-Based Nanoprobe for Bioimaging and Selective Recognition of Dipicolinic Acid and Cysteine by a Sensing Ensemble Approach

Multiple functions incorporated in one single-component nanoplatform pave the way for important biomedicine applications. Herein, a multifunctional terbium-doped gadolinium orthophosphate (GdPO₄:Tb-EDTA) nanoplatform was prepared through a simple, ecofriendly, one-step hydrothermal method. Results showed that dipicolinic acid (DPA), the biomarker of bacterial spores, significantly increased the fluorescence intensity of this nanoplatform and conferred it with rapid response and excellent selectivity. Subsequently, the fluorescence of the ensemble GdPO₄:Tb-EDTA-DPA can be remarkably quenched by Cu²⁺, which led to a rewritable nanosensor used in the detection of cysteine (Cys) with excellent sensitivity. In addition, GdPO₄:Tb-EDTA can also be a potential T₁-weighted magnetic resonance imaging (MRI) contrast agent, which indicated a satisfactory in vitro MRI with r₁ relaxivity values of 13.9 mM^-1 s^-1 and in vivo MRI through intravenous administration on a rat model. Overall, the proposed assay may have great theoretical and practical significance for designing multifunctional biomaterials.

Bisphosphonate Functionalized Gadolinium Oxide Nanoparticles Allow Long-Term MRI/CT Multimodal Imaging of Calcium Phosphate Bone Cement

Direct in vivo monitoring of bioconstructs using noninvasive imaging modalities such as magnetic resonance imaging (MRI) or computed tomography (CT) is not possible for many materials. Calcium phosphate-based composites (CPCs) that are applicable to bone regeneration are an example where the materials have poor MRI and CT contrast; hence, they are challenging to detect in vivo. In this study, a CPC construct is designed with gadolinium-oxide nanoparticles incorporated to act as an MRI/CT multimodal contrast agent. The gadolinium(III) oxide nanoparticles are synthesized via the polyol method and surface functionalized with a bisphosphonate (BP) derivative to give a construct (gadolinium-based contrast agents (GBCAs)-BP) with strong affinity toward calcium phosphate. The CPC-GBCAs-BP functional material is longitudinally monitored after in vivo implantation in a condyle defect rat model. The synthetic method developed produces nanoparticles that are stable in aqueous solution (hydrodynamic diameter 70 nm) with significant T₁ and T₂ relaxivity demonstrated in both clinical 3 T and preclinical 11.7 T MRI systems. The combination of GBCAs-BP nanoparticles with CPC gives an injectable material with handling properties that are suitable for clinical applications. The BP functionalization prolongs the residence of the contrast agent within the CPC to allow long-term follow-up imaging studies. The useful contrast agent properties combined with biological compatibility indicate further investigation of the novel bone substitute hybrid material toward clinical application.

Construction of Hybrid Alginate Nanogels Loaded with Manganese Oxide Nanoparticles for Enhanced Tumor Magnetic Resonance Imaging

Development of sensitive contrast agents for positive magnetic resonance (MR) imaging of biosystems still remains a great challenge. Herein, we report a facile process to construct hybrid alginate (AG) nanogels (NGs) loaded with manganese oxide (Mn₃O₄) nanoparticles (NPs) for enhanced tumor MR imaging. The obtained AG/PEI-Mn₃O₄ NGs with a mean size of 141.6 nm display excellent colloidal stability in aqueous solution and good cytocompatibility in the studied concentration range. Moreover, the hybrid NGs have a high r₁ relaxivity of 26.12 mM^-1 s^-1, which is about 19.5 times higher than that of PEI-Mn₃O₄ NPs with PEI surface amine acetylated (PEI.Ac-Mn₃O₄ NPs). Furthermore, the AG/PEI-Mn₃O₄ NGs presented longer blood circulation time and better tumor MR imaging performances in vivo than PEI.Ac-Mn₃O₄ NPs. With the good biosafety confirmed by histological examinations, the developed AG/PEI-Mn₃O₄ NGs may be potentially used as an efficient contrast agent for enhanced MR imaging of different biosystems.

Stable and non-toxic ultrasmall gadolinium oxide nanoparticle colloids (coating material = polyacrylic acid) as high-performance T1 magnetic resonance imaging contrast agents

For use as positive (T₁) magnetic resonance imaging contrast agents (MRI-CAs), gadolinium oxide (Gd₂O₃) nanoparticle colloids (i.e. nanoparticles coated with hydrophilic ligands) should be stable, non-toxic, and ultrasmall in particle diameter for renal excretion. In addition, they should have a high longitudinal water proton relaxivity (r₁) and r₂/r₁ ratio that is close to one (r₂ = transverse water proton relaxivity) for high-performance. In this study, we report ultrasmall Gd₂O₃ nanoparticle colloids [coating material = polyacrylic acid, M_w = ∼5100 Da] satisfying these conditions. The particle diameter was monodisperse with an average value of 2.0 ± 0.1 nm. The colloidal suspension exhibited a high r₁ value of 31.0 ± 0.1 s⁻¹ mM⁻¹ and r₂/r₁ ratio of 1.2, where r₁ was ∼8 times higher than that of commercial Gd-chelates: the cooperative induction model was proposed to explain this. The effectiveness of the colloidal suspension as a high-performance T₁ MRI-CA was confirmed by taking in vivo T₁ MR images in a mouse after intravenous administration. Highly positive contrast enhancements were observed in various organs of the mouse such as the liver, kidneys, and bladder. The colloidal suspension was then excreted through the bladder.

Stable and non-toxic ultrasmall Gd₂O₃ nanoparticle colloids as high-performance T₁ MRI-CA were developed.

Tumor-targeted nanoprobes for enhanced multimodal imaging and synergistic photothermal therapy: core-shell and dumbbell Gd-tailored gold nanorods

Multifunctional nanoprobes, due to their unique nanocomposite structures, have prominent advantages that combine multimodal imaging of a tumor with photothermal therapy. However, they remain a challenge for constructing nanostructures via conventional approaches due to the peculiar environmental sensitivity of each component. Here, we report the design and synthesis of Gd-based nanoparticle-tailored gold nanorods with distinctive core-shell and dumbbell nanoarchitectures (NAs) by a specific synthesis technology. The prepared NAs possess a tunable particle size of 80-120 nm in length and 50-90 nm in diameter, which are suitable for cellular uptake and passive targeting of a tumor. The formation of two distinct heterostructures and their underlying mechanism were studied through systematic investigations on the controllable synthesis process. The as-prepared nanoprobes possess an ultrahigh longitudinal relaxivity (r₁) of 22.69 s^-1 mM^-1 and thus a significant magnetic resonance imaging signal enhancement has been observed in mice tumors. The NAs, especially the dumbbell type, show a vivid two-photon cell imaging and a remarkable photothermal conversion efficiency owing to their superior longitudinal surface plasmon resonance. Both in vitro cytotoxicity and in vivo immunotoxicity assays give substantial evidence of excellent biocompatibility attained in the NAs. The development of multifunctional targeting nanoprobes in this study could provide guidance for tailored design and controllable synthesis of heterostructured nanocomposites utilized for multimodal imaging and photothermal therapy of cancer.

Enhancing T1 magnetic resonance imaging contrast with internalized gadolinium(III) in a multilayer nanoparticle

Multifunctional nanoparticles for biomedical applications have shown extraordinary potential as contrast agents in various bioimaging modalities, near-IR photothermal therapy, and for light-triggered therapeutic release processes. Over the past several years, numerous studies have been performed to synthesize and enhance MRI contrast with nanoparticles. However, understanding the MRI enhancement mechanism in a multishell nanoparticle geometry, and controlling its properties, remains a challenge. To systematically examine MRI enhancement in a nanoparticle geometry, we have synthesized MRI-active Au nanomatryoshkas. These are Au core-silica layer-Au shell nanoparticles, where Gd(III) ions are encapsulated within the silica layer between the inner core and outer Au layer of the nanoparticle (Gd-NM). This multifunctional nanoparticle retains its strong near-IR Fano-resonant optical absorption properties essential for photothermal or other near-IR light-triggered therapy, while simultaneously providing increased T₁ contrast in MR imaging by concentrating Gd(III) within the nanoparticle. Measurements of Gd-NM revealed a strongly enhanced T₁ relaxivity (r₁ ∼ 24 mM^-1⋅s^-1) even at 4.7 T, substantially surpassing conventional Gd(III) chelating agents (r₁ ∼ 3 mM^-1⋅s^-1 at 4.7 T) currently in clinical use. By varying the thickness of the outer gold layer of the nanoparticle, we show that the observed relaxivities are consistent with Solomon-Bloembergen-Morgan (SBM) theory, which takes into account the longer-range interactions between the encapsulated Gd(III) and the protons of the H₂O molecules outside the nanoparticle. This nanoparticle complex and its MRI T₁-enhancing properties open the door for future studies on quantitative tracking of therapeutic nanoparticles in vivo, an essential step for optimizing light-induced, nanoparticle-based therapies.

Nanoscale hydrophilic colloids with high relaxivity and low cytotoxicity based on Gd(iii) complexes with Keplerate polyanions

Efficient hydrophilic stabilization of Gd(iii) complexes with Keplerate polyanions for high relaxivity, colloid stability and low cytotoxicity.

Synthesis of gadolinium oxide nanodisks and gadolinium doped iron oxide nanoparticles for MR contrast agents

Herein, we report the synthesis of differently sized gadolinium oxide nanodisks and gadolinium doped iron oxide spherical and cubic nanoparticles through the thermal decomposition of an oleate precursor.

Fluorescence-tagged amphiphilic brush copolymer encapsulated Gd2O3 core-shell nanostructures for enhanced T 1 contrast effect and fluorescent imaging

To obtain suitable T 1 contrast agents for magnetic resonance imaging (MRI) application, aqueous Gd2O3 nanoparticles (NPs) with high longitudinal relativity (r 1) are demanded. High quality Gd2O3 NPs are usually synthesized through a non-hydrolytic route which requires post-synthetic modification to render the NPs water soluble. The current challenge is to obtain aqueous Gd2O3 NPs with high colloidal stability and enhanced r 1 relaxivity. To overcome this challenge, fluorescence-tagged amphiphilic brush copolymer (AFCP) encapsulated Gd2O3 NPs were proposed as suitable T 1 contrast agents. Such a coating layer provided (i) superior aqueous stability, (ii) biocompatibility, as well as (iii) multi-modality (conjugation with fluorescence dye). The polymeric coating layer thickness was simply adjusted by varying the phase-transfer parameters. By reducing the coating thickness, i.e. the distance between the paramagnetic centre and surrounding water protons, the r 1 relaxivity could be enhanced. In contrast, a thicker polymeric layer coating prevents Gd(3+) ions leakage, thus improving its biocompatibility. Therefore, it is important to strike a balance between the biocompatibility and the r 1 relaxivity behaviour. Lastly, by conjugating fluorescence moiety, an additional imaging modality was enabled, as demonstrated from the cell-labelling experiment.

Water bridge coordination on the metal-rich facets of Gd2O3 nanoplates confers high T1 relaxivity

The realization of the nature of water coordination on the solid surfaces may provoke an essential understanding of T1 relaxation enhancement, especially in nanoparticulate systems. We report herein that the T1 relaxivity of Gd2O3 nanoplates is highly dependent on water coordinating behaviors on different surfaces. Gd2O3 nanoplates with metal-rich {100} facets showed an approximately 4-fold higher r1 value compared to that with oxygen-terminated {111} facets. Density functional theory (DFT) calculations show that the enhanced T1 relaxivity of Gd2O3 {100} nanoplates may be ascribed to the high density of accessible Gd3+, fast exchange of water, and more importantly, multicenter (one-to-two) coordination for water molecules with magnetic centers on the metal-rich surface.

Structural and optical properties of thermal decomposition assisted Gd2O3:Ho(3+)/Yb(3+) upconversion phosphor annealed at different temperatures

The infrared to visible upconversion fluorescent nanoparticles of Ho(3+)/Yb(3+) codoped Gd2O3 phosphor is synthesized via thermal decomposition route. The as-synthesized sample was annealed at 800, 1000 and 1200°C for 3h and then structural and optical properties were studied. The Rietveld refinement of X-ray diffraction (XRD) data was analyzed to probe the effect of Ho(3+)/Yb(3+) dopant on the structural parameters of Gd2O3 host. The upconversion emission spectra of as-synthesized and annealed samples are compared using 980nm diode laser excitation and five emission bands noticed at 490, 539, 550, 667 and 757nm corresponding to the (5)F3→(5)I8, (5)F4→(5)I8, (5)S2→(5)I8,(5)F5→(5)I8 and (5)I4→(5)I8 manifolds, respectively. The local temperature induced by laser light is also calculated. The fluorescence intensity ratio (FIR) of two thermally coupled transitions (5)F4→(5)I8 and (5)S2→(5)I8 is plotted against the sample temperature and sensor sensitivity of sample is calculated.

T1-Weighted MR imaging of liver tumor by gadolinium-encapsulated glycol chitosan nanoparticles without non-specific toxicity in normal tissues

Herein, we have synthesized Gd(iii)-encapsulated glycol chitosan nanoparticles (Gd(iii)-CNPs) for tumor-targeted T1-weighted magnetic resonance (MR) imaging. The T1 contrast agent, Gd(iii), was successfully encapsulated into 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-modified CNPs to form stable Gd(iii)-encapsulated CNPs (Gd(iii)-CNPs) with an average particle size of approximately 280 nm. The stable nanoparticle structure of Gd(iii)-CNPs is beneficial for liver tumor accumulation by the enhanced permeation and retention (EPR) effect. Moreover, the amine groups on the surface of Gd(iii)-CNPs could be protonated and could induce fast cellular uptake at acidic pH in tumor tissue. To assay the tumor-targeting ability of Cy5.5-labeled Gd(iii)-CNPs, near-infrared fluorescence (NIRF) imaging and MR imaging were used in a liver tumor model as well as a subcutaneous tumor model. Cy5.5-labeled Gd(iii)-CNPs generated highly intense fluorescence and T1 MR signals in tumor tissues after intravenous injection, while DOTAREM®, the commercialized control MR contrast agent, showed very low tumor-targeting efficiency on MR images. Furthermore, damaged tissues were found in the livers and kidneys of mice injected with DOTAREM®, but there were no obvious adverse effects with Gd(iii)-CNPs. Taken together, these results demonstrate the superiority of Gd(iii)-CNPs as a tumor-targeting T1 MR agent.

Small is Smarter: Nano MRI Contrast Agents - Advantages and Recent Achievements

Many challenges for advanced sensitive and noninvasive clinical diagnostic imaging remain unmatched. In particular, the great potential of magnetic nano-probes is intensively discussed to further improve the performance of magnetic resonance imaging (MRI), especially for cancer diagnosis. Based on recent achievements, here the concepts of magnetic nanoparticle-based MRI contrast agents and tumor-specific imaging probes are critically summarized. Advances in their synthesis, biocompatible chemical and biofunctional surface modifications, and current strategies for further developing them into multimodality imaging probes are discussed. In addition, how engineered versus unintended surface coatings such as protein coronas affect the biocompatibility and performance of MRI nano-probes is also considered. To stimulate progress in the field, future strategies and relevant challenges that still need to be resolved in the field conclude this review.

Smart polymeric particle encapsulated gadolinium oxide and europium: theranostic probes for magnetic resonance/optical imaging and antitumor drug delivery

Paramagnetic, luminescent, and temperature/pH-responsive polymeric particles with MR/optical imaging and antitumor drug delivery capability are prepared by emulsifier-free emulsion polymerization.

Multifunctional Eu-doped NaGd(MoO4)2 nanoparticles functionalized with poly(l-lysine) for optical and MRI imaging

Eu:NaGd(MoO₄)₂ nanoparticles functionalized with poly(l-lysine) have been fabricated, which exhibit visible red luminescence and good relaxivity values making them suitable for MRI and optical imaging.

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.

Designed synthesis of multi-functional PEGylated Yb2O3:Gd@SiO2@CeO2 islands core@shell nanostructure

We produce the core@shell structure of PEGylated Yb₂O₃:Gd@SiO₂@CeO₂ islands, which exhibit a high-performance dual-modal contrast agent in MRI and CT and excellent catalase mimetic activity.

Highly monodisperse low-magnetization magnetite nanocubes as simultaneous T(1)-T(2) MRI contrast agents

We report the first study of highly monodisperse and crystalline iron oxide nanocubes with sub-nm controlled size distribution (9.7 ± 0.5 nm in size) that achieve simultaneous contrast enhancement in both T1- and T2-weighted magnetic resonance imaging (MRI). Here, we confirmed the magnetite structure of iron oxide nanocubes by X-ray diffraction (XRD), selected area electron diffraction (SAED) pattern, optical absorption and Fourier transformed infrared (FT-IR) spectra. These magnetite nanocubes exhibit superparamagnetic and paramagnetic behavior simultaneously by virtue of their finely controlled shape and size. The magnetic measurements reveal that the magnetic moment values are favorably much lower because of the small size and cubic shape of the nanoparticles, which results in an enhanced spin canting effect. As a proof-of-concept demonstration, we showed their potential as dual contrast agents for both T1- and T2-weighted MRI via phantom studies, in vivo imaging and relaxivity measurements. Therefore, these low-magnetization magnetite nanocubes, while being non-toxic and bio-compatible, hold great promise as excellent dual-mode T1 and T2 contrast agents for MRI.

Nanostructured magnetic nanocomposites as MRI contrast agents

Magnetic resonance imaging (MRI) has become an integral part of modern clinical imaging due to its non-invasiveness and versatility in providing tissue and organ images with high spatial resolution. With the current MRI advancement, MRI imaging probes with suitable biocompatibility, good colloidal stability, enhanced relaxometric properties and advanced functionalities are highly demanded. As such, MRI contrast agents (CAs) have been an extensive research and development area. In the recent years, different inorganic-based nanoprobes comprising inorganic magnetic nanoparticles (MNPs) with an organic functional coating have been engineered to obtain a suitable contrast enhancement effect. For biomedical applications, the organic functional coating is critical to improve colloidal stability and biocompatibility. Simultaneously, it also provides a building block for generating a higher dimensional secondary structure. In this review, the combinatorial design approach by a self-assembling pre-formed hydrophobic inorganic MNPs core (from non-polar thermolysis synthesis) into various functional organic coatings (e.g. ligands, amphiphilic polymers and graphene oxide) to form water soluble nanocomposites will be discussed. The resultant magnetic ensembles were classified based on their dimensionality, namely, 0-D, 1-D, 2-D and 3-D structures. This classification provides further insight into their subsequent potential use as MRI CAs. Special attention will be dedicated towards the correlation between the spatial distribution and the associated MRI applications, which include (i) coating optimization-induced MR relaxivity enhancement, (ii) aggregation-induced MR relaxivity enhancement, (iii) off-resonance saturation imaging (ORS), (iv) magnetically-induced off-resonance imaging (ORI), (v) dual-modalities MR imaging and (vi) multifunctional nanoprobes.