Fabricating High-Performance T2-Weighted Contrast Agents via Adjusting Composition and Size of Nanomagnetic Iron Oxide

Dual drug-loaded metal-phenolic networks for targeted magnetic resonance imaging and synergistic chemo-chemodynamic therapy of breast cancer

The development of nanomedicines with simplified compositions and synergistic theranostic functionalities remains a great challenge. Herein, we develop a simple method to integrate both atovaquone (ATO, a mitochondrial inhibitor) and cisplatin within tannic acid (TA)-iron (Fe) networks coated with hyaluronic acid (HA) for targeted magnetic resonance (MR) imaging-guided chemo-chemodynamic synergistic therapy. The formed TFP@ATO-HA displayed good colloidal stability with a mean size of 95.5 nm, which could accumulate at tumor sites after circulation and be specifically taken up by metastatic 4T1 cells overexpressing CD44 receptors. In the tumor microenvironment, TFP@ATO-HA could release ATO/cisplatin and Fe3+ in a pH-responsive manner, deplete glutathione, and generate reactive oxygen species with endogenous H2O2 for chemodynamic therapy (CDT). Additionally, ATO could enhance chemotherapeutic efficacy by inhibiting mitochondrial respiration, relieving hypoxia, and amplifying the CDT effect by decreasing intracellular pH and elevating Fenton reaction efficiency. In vivo experiments demonstrated that TFP@ATO-HA could effectively inhibit tumor growth and suppress lung metastases without obvious systemic toxicity. Furthermore, TFP@ATO-HA exhibited a r1 relaxivity of 2.6 mM-1 s-1 and targeted MR imaging of 4T1 tumors. Dual drug-loaded metal-phenolic networks can be easily prepared and act as effective theranostic nanoplatforms for targeted MR imaging and synergistic chemo-chemodynamic therapy.

PDGFB-targeted functional MRI nanoswitch for activatable T1-T2 dual-modal ultra-sensitive diagnosis of cancer

As one of the most significant imaging modalities currently available, magnetic resonance imaging (MRI) has been extensively utilized for clinically accurate cancer diagnosis. However, low signal-to-noise ratio (SNR) and low specificity for tumors continue to pose significant challenges. Inspired by the distance-dependent magnetic resonance tuning (MRET) phenomenon, the tumor microenvironment (TME)-activated off-on T₁-T₂ dual-mode MRI nanoswitch is presented in the current study to realize the sensitive early diagnosis of tumors. The tumor-specific nanoswitch is designed and manufactured on the basis of PDGFB-conjugating ferroferric oxide coated by Mn-doped silica (PDGFB-FMS), which can be degraded under the high-concentration GSH and low pH in TME to activate the T₁-T₂ dual-mode MRI signals. The tumor-specific off-on dual-mode MRI nanoswitch can significantly improve the SNR and is used successfully for the accurate diagnosis of early-stage tumors, particularly for orthotopic prostate cancer. In addition, the systemic delivery of the nanoswitch did not cause blood or tissue damage, and it can be excreted out of the body in a timely manner, demonstrating excellent biosafety. Overall, the strategy is a significant step in the direction of designing off-on dual-mode MRI nanoprobes to improve imaging accuracy, which opens up new avenues for the development of new MRI probes.

Transition-metal-doped hydrophilic ultrasmall iron oxide modulates MRI contrast performance for accurate diagnosis of orthotopic prostate cancer

The FDA-approved iron oxide nanocrystals (IONs), as negative magnetic resonance imaging contrast agents (MRICAs), face challenges because of their low relaxation rate and coherent ferromagnetism. Although research has found that metal doping is an efficient approach to improve the magnetic property and MRI contrast performance of IONs, their systemic mechanism has not been fully explained. Herein, we fabricated a series of transition-metal-doped IONs and systemically explored their sizes, structures, and variation in magnetic properties, revealing the oxygen vacancy-mediated MRI contrast enhancement mechanism of transition-metal-doped IONs. Based on these, we found that Zn-doped IONs possess optimal T₂ MRI contrast performance and further investigated their potential to diagnose in vivo orthotopic tumor as a T₂ contrast agent. The results indicate that the use of Zn-doped IONs significantly enhances T₂-weighted MRI signal intensity of orthotopic prostate tumor with low toxicity, which is beneficial for the accurate diagnosis of orthotopic tumor. Collectively, this work clearly illustrates the mechanism of contrast enhancement of transition-metal-doped IONs and provides a novel paradigm for developing a highly efficient T₂ contrast agent.

Approaches on Ferrofluid Synthesis and Applications: Current Status and Future Perspectives

Ferrofluids are colloidal suspensions of iron oxide nanoparticles (IONPs) within aqueous or nonaqueous liquids that exhibit strong magnetic properties. These magnetic properties allow ferrofluids to be manipulated and controlled when exposed to magnetic fields. This review aims to provide the current scope and research opportunities regarding the methods of synthesis of nanoparticles, surfactants, and carrier liquids for ferrofluid production, along with the rheology and applications of ferrofluids within the fields of medicine, water treatment, and mechanical engineering. A ferrofluid is composed of IONPs, a surfactant that coats the magnetic IONPs to prevent agglomeration, and a carrier liquid that suspends the IONPs. Coprecipitation and thermal decomposition are the main methods used for the synthesis of IONPs. Despite the fact that thermal decomposition provides precise control on the nanoparticle size, coprecipitation is the most used method, even when the oxidation of iron can occur. This oxidation alters the ratio of maghemite/magnetite, influencing the magnetic properties of ferrofluids. Strategies to overcome iron oxidation have been proposed, such as the use of an inert atmosphere, adjusting the Fe(II) and Fe(III) ratio to 1:2, and the exploration of other metals with the oxidation state +2. Surfactants and carrier liquids are chosen according to the ferrofluid application to ensure stability. Hence, a compatible carrier liquid (polar or nonpolar) is selected, and then, a surfactant, mainly a polymer, is embedded in the IONPs, providing a steric barrier. Due to the variety of surfactants and carrier liquids, the rheological properties of ferrofluids are an important response variable evaluated when synthesizing ferrofluids. There are many reported applications of ferrofluids, including biosensing, medical imaging, medicinal therapy, magnetic nanoemulsions, and magnetic impedance. Other applications include water treatment, energy harvesting and transfer, and vibration control. To progress from synthesis to applications, research is still ongoing to ensure control of the ferrofluids' properties.

Magnetic Relaxation Switching Immunoassay Based on Hydrogen Peroxide-Mediated Assembly of Ag@Au-Fe3 O4 Nanoprobe for Detection of Aflatoxin B1

Magnetic relaxation switching (MRS) sensors have shown great potential in food safety monitoring due to their high signal-to-noise ratio and simplicity, but they often suffer from insufficient sensitivity and stability due to the lack of excellent magnetic nanoprobes. Herein, dumbbell-like Au-Fe₃ O₄ nanoparticles are designed as magnetic nanoprobes for developing an aflatoxin B1-MRS immunosensor. The Fe₃ O₄ portion in the Au-Fe₃ O₄ nanoparticles functions as the magnetic probe to provide transverse relaxation signals, while the Au segments serve as a bridge to grow Ag shell and assemble the Au-Fe₃ O₄ nanoparticles, thus modulating transverse relaxation time of surrounding water molecular. The formation of Ag@Au-Fe₃ O₄ is triggered by hydrogen peroxide. After degraded by horseradish peroxidase, hydrogen peroxide reduces Ag⁺ to Ag nanoparticles which assemble dispersed Au-Fe₃ O₄ to aggregated Ag@Au-Fe₃ O₄ , thus dramatically improving the sensitivity of traditional MRS sensor. Combined with competitive immunoreaction, this Ag@Au-Fe₃ O₄ -MRS immunosensor can detect aflatoxin B1 with a high sensitivity (3.81 pg mL^-1 ), which improved about 21 folds and 9 folds than those of enzyme-linked immunosorbent assay and high-performance liquid chromatography (HPLC), respectively. The good consistency with HPLC in real samples detection indicates the good accuracy of this immunosensor. This Ag@Au-Fe₃ O₄ -MRS immunosensor offers an attractive tool for detection of harmful substances.

Hydrolytically stable foamed HKUST-1@CMC composites realize high-efficient separation of U(VI)

HKUST-1@CMC (HK@CMC) composites that show good acid and alkali resistance and radiation resistance were successfully synthesized by introducing carboxymethyl cellulose (CMC) onto the surface of HKUST-1 using a foaming strategy. For the first time, the composites were explored as efficient adsorbents for U(VI) trapping from aqueous solution, with encouraging results of large adsorption capacity, fast adsorption kinetics, and desirable selectivity toward U(VI) over a series of competing ions. More importantly, a hybrid derivative film was successfully prepared for the dynamic adsorption of U(VI). The results show that ∼90% U(VI) can be removed when 45 mg L-1 U(VI) was passed through the film one time, and the removal percentage is still more than 80% even after four adsorption-desorption cycles, ranking one of the most practical U(VI) scavengers. This work offers new clues for application of the Metal-organic-framework-based materials in the separation of radionuclides from wastewater.

A nanoselenium-coating biomimetic cytomembrane nanoplatform for mitochondrial targeted chemotherapy- and chemodynamic therapy through manganese and doxorubicin codelivery

The cell membrane is widely considered as a promising delivery nanocarrier due to its excellent properties. In this study, self-assembled Pseudomonas geniculate cell membranes were prepared with high yield as drug nanocarriers, and named BMMPs. BMMPs showed excellent biosafety, and could be more efficiently internalized by cancer cells than traditional red cell membrane nanocarriers, indicating that BMMPs could deliver more drug into cancer cells. Subsequently, the BMMPs were coated with nanoselenium (Se), and subsequently loaded with Mn²⁺ ions and doxorubicin (DOX) to fabricate a functional nanoplatform (BMMP-Mn²⁺/Se/DOX). Notably, in this nanoplatform, Se nanoparticles activated superoxide dismutase-1 (SOD-1) expression and subsequently up-regulated downstream H₂O₂ levels. Next, the released Mn²⁺ ions catalyzed H₂O₂ to highly toxic hydroxyl radicals (·OH), inducing mitochondrial damage. In addition, the BMMP-Mn²⁺/Se nanoplatform inhibited glutathione peroxidase 4 (GPX4) expression and further accelerated intracellular reactive oxygen species (ROS) generation. Notably, the BMMP-Mn²⁺/Se/DOX nanoplatform exhibited increased effectiveness in inducing cancer cell death through mitochondrial and nuclear targeting dual-mode therapeutic pathways and showed negligible toxicity to normal organs. Therefore, this nanoplatform may represent a promising drug delivery system for achieving a safe, effective, and accurate cancer therapeutic plan.

Biocompatible Superparamagnetic Europium-Doped Iron Oxide Nanoparticle Clusters as Multifunctional Nanoprobes for Multimodal In Vivo Imaging

Magnetic nanoparticle clusters composed of primary magnetic nanoparticles can not only significantly enhance the magnetic properties of the assembly but also retain the superparamagnetic properties of the individual primary nanoparticle, which is of great significance for promoting the development of multifunctional advanced materials. Herein, water-soluble biocompatible and superparamagnetic europium-doped iron oxide nanoparticle clusters (EuIO NCs) were directly synthesized by a simple one-pot method. The obtained EuIO NCs have excellent water solubility, colloidal stability, and biocompatibility. Europium doping significantly improved the contrast enhancement effect of EuIO NCs in T1-weighted MR imaging. In addition, EuIO NCs can be functionalized by active molecules, and the rhodamine123-functionalized EuIO NCs have long circulation time and excellent fluorescence imaging performance in vivo. This study provides a simple strategy for the design and construction of a novel multifunctional magnetic nanoplatform and provides solutions for the development of multimodal imaging probes and the diagnosis of disease.

Fluorine-mediated synthesis of anisotropic iron oxide nanostructures for efficient T2-weighted magnetic resonance imaging

Herein, we developed a novel strategy for the shape-controlled synthesis of iron oxide nanostructures with superior r2 values through the introduction of fluoride ions as a morphology controlling agent and dopant. The selective adsorption of fluoride ions onto the specified crystal planes of iron oxide nanocrystals leads to the formation of octapod nanoparticles (ONPs) and cubic nanocrystal clusters (CNCs). Both ONPs and CNCs present high r2 values (526.5 and 462.2 mM-1 s-1, respectively) due to the synergistic effect of a larger effective radius, clustering and fluorine doping. The in vivo MRI results show significant enhancement in T2-weighted images of the liver after the intravenous injection of ONPs and CNCs, suggesting their great potential as efficient T2-weighted MRI contrast agents. This new approach of achieving anisotropic fluorine-doped iron oxide nanostructures with high r2 relaxivity provides an alternative strategy for the development of highly sensitive T2 contrast agents for MRI.

Highly sensitive T1-T2dual-mode MRI probe based on ultra-small gadolinium oxide-decorated iron oxide nanocrystals

Single-mode magnetic resonance imaging (MRI) contrast agents (CAs) in clinical settings are easily disturbed by calcification, bleeding, and adipose signals, which result in inaccurate diagnoses. In this study, we developed a highly efficient T₁-T₂dual-mode MRI CA using an ultra-small gadolinium oxide-decorated magnetic iron oxide nanocrystal (GMIO). The gadolinium element could effectively alter the magnetic properties of the GMIO from soft-ferromagnetism to superparamagnetism. In addition, when the Gd/Fe ratio was 15 % (designated as GMIO-2), the GMIO-2 possessed the best superparamagnetism and highest magnetism. Subsequently, T₁and T₂values of GMIO-2 were measured through a series of turbo spin-echo images and then multi-spin echo (MSE) sequence, respectively. Based on this, T₁and T₂relaxivities of GMIO-2 were calculated and were the highest (r₁: 1.306 m M^-1s^-1and r₂: 234.5 m M^-1s^-1) when compared to other groups. The cytotoxicity of GMIO-2 was negligible under a wide range of dosages, thus exhibiting excellent cell biocompatibility. Moreover, GMIO-2 could quickly diffuse into cells, leading to its effective accumulation. The systemic delivery of GMIO-2 resulted in an excellent T₁-T₂dual-mode MRI contrast effect in kidneys, which is expected to improve the diagnosis of kidney lesions. Therefore, this work provides a promising candidate for the development of a T₁-T₂dual-mode MRI CA.

Libraries of Uniform Magnetic Multicore Nanoparticles with Tunable Dimensions for Biomedical and Photonic Applications

Multicore iron oxide nanoparticles, also known as colloidal nanocrystal clusters, are magnetic materials with diverse applications in biomedicine and photonics. Here, we examine how both of their characteristic dimensional features, the primary particle and sub-micron colloid diameters, influence their magnetic properties and performance in two different applications. The characterization of these basic size-dependent properties is enabled by a synthetic strategy that provides independent control over both the primary nanocrystal and cluster dimensions. Over a wide range of conditions, electron microscopy and X-ray diffraction reveal that the oriented attachment of smaller nanocrystals results in their crystallographic alignment throughout the entire superstructure. We apply a sulfonated polymer with high charge density to prevent cluster aggregation and conjugate molecular dyes to particle surfaces so as to visualize their collection using handheld magnets. These libraries of colloidal clusters, indexed both by primary nanocrystal dimension (d_p) and overall cluster diameter (D_c), form magnetic photonic crystals with relatively weak size-dependent properties. In contrast, their performance as MRI T₂ contrast agents is highly sensitive to cluster diameter, not primary particle size, and is optimized for materials of 50 nm diameter (r₂ = 364 mM^-1 s^-1). These results exemplify the relevance of dimensional control in developing applications for these versatile materials.

Magnetic Nanoparticles as MRI Contrast Agents

Iron oxide nanoparticles (IONPs) have emerged as a promising alternative to conventional contrast agents (CAs) for magnetic resonance imaging (MRI). They have been extensively investigated as CAs due to their high biocompatibility and excellent magnetic properties. Furthermore, the ease of functionalization of their surfaces with different types of ligands (antibodies, peptides, sugars, etc.) opens up the possibility of carrying out molecular MRI. Thus, IONPs functionalized with epithelial growth factor receptor antibodies, short peptides, like RGD, or aptamers, among others, have been proposed for the diagnosis of various types of cancer, including breast, stomach, colon, kidney, liver or brain cancer. In addition to cancer diagnosis, different types of IONPs have been developed for other applications, such as the detection of brain inflammation or the early diagnosis of thrombosis. This review addresses key aspects in the development of IONPs for MRI applications, namely, synthesis of the inorganic core, functionalization processes to make IONPs biocompatible and also to target them to specific tissues or cells, and finally in vivo studies in animal models, with special emphasis on tumor models.

Promoting desert biocrust formation using aquatic cyanobacteria with the aid of MOF-based nanocomposite

Desertification and eutrophication are two global environmental problems human beings face. Inoculating cyanobacteria to form biocrusts is considered an effective technology to inhibit desertification. The main limitation of biocrust formation is the lack of propagules and nutrients in deserts. A possible low cost source of propagules and nutrients is eutrophic water containing aquatic cyanobacteria (AC), nitrogen and phosphorus. In this study, we fabricated a network-structured nanocomposite (designated as MC) using a metal-organic framework (MOF) and carboxymethyl cellulose (CMC). MC, with a large specific surface area and numerous surface groups, had a high retention capacity for water and nutrients and good biosafety. The combination of AC-containing water (ACW) and MC could provide a suitable microenvironment in the soil, promote the growth of desert cyanobacteria (DC), formation of biocrusts and inhibition of desertification. This study provides a novel approach to simultaneously relieve desertification and eutrophication.

Gd3+-nanoparticle-enhanced multivalent biosensing that combines magnetic relaxation switching and magnetic separation

In this work, we developed a multivalent magnetic biosensing strategy by integrating magnetic separation and magnetic relaxation switching (MRS) where Gd³⁺-loaded magnetic nanoparticles acted as the probe. As a transition metal ion, Gd³⁺ has multiple unpaired electrons in the d-orbitals that can induce a strong fluctuating magnetic field and thus can reduce the transverse relaxation time (T₂), contributing to a strong magnetic signal. By loading Gd³⁺ onto magnetic nanoparticles, we prepared a multivalent magnetic probe that combined magnetic separation and MRS for the signal readout. This multivalent sensing technique simplified the procedures and greatly enhanced the detection sensitivity of conventional MRS assays. A sensitive detection of ractopamine in real samples has been demonstrated with this multivalent sensing technique. The magnetic probe enabled the detection of ractopamine in a linear range from 0.1 to 100 ng/mL and the limit of detection was 20 pg/mL, a 25-fold enhancement in the sensitivity compared with conventional MRS assays. This Gd³⁺-nanoparticle-mediated MRS biosensor is a potential magnetic platform to detect trace levels of targets in complex samples.

Enzyme-instructed self-aggregation of Fe3O4 nanoparticles for enhanced MRI T2 imaging and photothermal therapy of tumors

The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles (NPs) can greatly enhance magnetic resonance imaging (MRI) T2-weighted imaging and near-infrared (NIR) absorption in experiments. In this study, an Ac-Arg-Val-Arg-Arg-Cys(StBu)-Lys-CBT probe was designed and coupled with monodispersed carboxyl-decorated SPIO NPs to form SPIO@1NPs, which use it for intracellular self-aggregation. In vitro experiments showed that the self-aggregation of SPIO@1NPs was induced by a condensation reaction mediated by the enzyme furin in furin-overexpressing tumor cells. Moreover, the NPs in the aggregated state showed significantly higher MR r2 values and photothermal conversion efficiency than the NPs in the monodisperse state. Then, the in vivo SPIO@1NP self-aggregation in tumors can facilitate accurate MRI T2 imaging-guided photothermal therapy for effectively killing cancer cells. We believe that this basic technique, based on tumor-specific enzyme-instructed intracellular self-aggregation of NPs, could be useful for the rational synthesis of other inorganic NPs for use in the fields of tumor diagnosis and treatment.

A T1/T2 dual functional iron oxide MRI contrast agent with super stability and low hypersensitivity benefited by ultrahigh carboxyl group density

Clinically acceptable safety and efficacy are the most important issues for the design and synthesis of iron oxide MRI contrast agents. In order to meet the practical requirements, a kind of low molecular weight PAA-coated Fe₃O₄ nanoparticle (CS015) with super colloidal stability and low hypersensitivity benefitting from an ultrahigh carboxyl group density was developed in this study. The composition and physicochemical properties of the particles were characterized by TEM, XRD, FTIR and TGA. The ultrahigh density of COOH on the particles (33 COOH per nm²) was verified while a core size of 5.1 nm and a dynamic diameter of 41 nm with a narrow distribution were also achieved. The particles still showed excellent dispersity and stability even after a spray-drying or freeze-drying process, exposure to high temperature sterilized conditions and long-term storage. The nanoparticles could quickly capture iron ions in bulk solution which was confirmed by ITC results, and the bioactive iron concentration of CS015 was greatly decreased (0.54 ± 0.05 mg L^-1) compared to that of commercially available ferumoxytol, iron sucrose and VSOP. Free iron ion release was 1120 times lower than the toxic concentration of iron. An excellent biocompatibility of CS015 with no obvious cytotoxicity and low risk of hypersensitivity has been manifested by cytotoxicity experiments and a passive cutaneous anaphylaxis test. The T₁ and T₂-weighted MRI contrast effects both in vitro and in vivo have also been verified which made CS015 a potential dual MRI contrast agent. Furthermore, theoretically calculated conformation was speculated and all the advantages mentioned above were benefited from the three dimensional brush-like texture of CS015. Therefore, these merits make the CS015 nanoplatform highly suitable in diagnostic applications as a MRI contrast agent.

Iron-oxide-based twin nanoplates with strong T2 relaxation shortening for contrast-enhanced magnetic resonance imaging

Iron oxide nanomaterials have been intensively investigated over the past few decades as magnetic resonance imaging (MRI) contrast agents (CAs) due to their favorable magnetism and excellent biocompatibility. However, commercial iron-oxide-nanoparticle-based CAs suffer from low T2 relaxivity, which significantly limits their applications in the biomedical field. Herein, we report a new type of iron oxide nanoplate (IOP) with an interesting twinning plane, which is fabricated via seed growth. Compared with the conventional iron oxide (IO) spherical nanoparticles, iron oxide twin nanoplates (IOP-13) have a larger effective radius, higher saturation magnetization, and greater anisotropy, resulting in their superior T2 relaxivity of 571.21 mM-1 s-1 at 0.5 T, which is about six times higher than that of commercial IO nanoparticles. In vivo MR imaging demonstrated that IOP-13 could be used for liver imaging and liver tumor diagnosis with high sensitivity and accuracy, revealing the great potential of IOP-13 as a next-generation CA. This work provides a novel strategy of structure tuning to devise high-performance T2 contrast agents, which expands the applications of iron oxide nanoparticles in biology and materials.