Mixed Metal Metal-Organic Frameworks Derived Carbon Supporting ZnFe2O4/C for High-Performance Magnetic Particle Imaging

Hollow Mesoporous Carbon Nanospheres Derived from Metal-Organic Frameworks for Efficient Sono-immunotherapy against Pancreatic Cancer

Sono-immunotherapy is expected to effectively enhance treatment efficacy and reduce mortality in patients with pancreatic cancer. Hence, efficient applicable sono-immunotherapy systems are urgently needed for the treatment of this condition. In this study, hollow mesoporous carbon (HMC) nanoparticles were prepared using the sacrificial template method. These nanoparticles had a porphyrin-like structure and could generate singlet oxygen more efficiently than commercial TiO2. Cellular assays showed that HMC killed tumor cells in the presence of ultrasonication, primarily by inducing apoptosis. HMC could also accelerate the release of immune factors by tumor cells, thereby activating dendritic cells and enhancing the efficacy of immunotherapy. Experiments in tumor-bearing mice and in situ pancreatic cancer tests showed that HMC, in combination with the small-molecule inhibitors of programmed cell death ligand 1, could reduce tumor growth via the generation of reactive oxygen species following ultrasonication. HMC could enhance the efficacy of immunotherapy by disrupting the immunosuppressive tumor microenvironment and promoting the accumulation of immune cells. Accordingly, in vivo sono-immunotherapy was achieved, and the growth of transplanted tumors and in situ tumors could be reduced. In conclusion, this study proposes a novel method for the preparation of HMC nanoparticles and demonstrates their potential in tumor treatment. Additionally, owing to their unique structure, these HMC nanoparticles could be used for different combination therapies tailored based on specific clinical requirements.

Exploring the diagnostic potential: magnetic particle imaging for brain diseases

Brain diseases are characterized by high incidence, disability, and mortality rates. Their elusive nature poses a significant challenge for early diagnosis. Magnetic particle imaging (MPI) is a novel imaging technique with high sensitivity, high temporal resolution, and no ionizing radiation. It relies on the nonlinear magnetization response of superparamagnetic iron oxide nanoparticles (SPIONs), allowing visualization of the spatial concentration distribution of SPIONs in biological tissues. MPI is expected to become a mainstream technology for the early diagnosis of brain diseases, such as cancerous, cerebrovascular, neurodegenerative, and inflammatory diseases. This review provides an overview of the principles of MPI, explores its potential applications in brain diseases, and discusses the prospects for the diagnosis and management of these diseases.

Optical-magnetic Imaging for Optimizing Lymphodepletion-TIL Combination Therapy in Breast Cancer

PURPOSE

Lymphodepletion before tumor-infiltrating lymphocytes (TIL) infusion can activate the immune system, enhance the release of homeostatic cytokines, and decrease the number of immunosuppressive cells. This process is crucial for improving the therapeutic efficacy of TIL therapy. However, the challenge of in vivo assessing TILs targeting tumors limits the optimization of lymphodepleting conditioning regimen (LDC).

PROCEDURES

This study aims to employ magnetic particle imaging (MPI) and fluorescence molecular imaging (FMI) to monitor TIL biodistribution in vivo and optimize LDC in triple-negative breast cancer TIL therapy. MPI provides quantitative imaging capabilities without depth limitations, effectively complementing the high sensitivity of FMI. The efficacy of different LDCs in enhancing TIL therapy was assessed using FMI, and MPI quantified the number of TILs accumulated in the 4T1 tumor.

RESULTS

TILs preserved viability, phenotypes, and anti-tumor efficacy after being labeled with superparamagnetic iron oxide and fluorescence dye DiR. The dual-modality imaging system effectively discerned variations in LDC treatments that enhanced TIL therapy. Compared to TIL monotherapy, lymphodepletion with TIL therapy improves tumor dual-modality imaging signal intensity, increases the expression of monocyte chemotactic protein-1 in serum and tumor tissue, and enhances the therapeutic effect of TILs.

CONCLUSION

Our results confirm the utility of optical-magnetic dual-modality imaging for tracking the biodistribution of TILs in vivo. With the help of optical-magnetic dual-modality imaging, we successfully optimize TIL combination therapy. Optical-magnetic dual-modality imaging provides a new approach to develop personalized immunotherapy strategies and mine potential therapeutic mechanisms for TIL.

A CLDN18.2-Targeted Nanoplatform Manipulates Magnetic Hyperthermia Spatiotemporally for Synergistic Immunotherapy in Gastric Cancer

Precision treatment of gastric cancer requires specific biomarkers, and CLDN18.2 emerges as a promising target for patients' stratification and therapeutic guidance. In 563 cases, 54.4% of patients are identified as CLDN18.2-positive, with CLDN18.2 expression negatively correlated with immune-related factors like PD-L1, indicating a "cold" tumor microenvironment. Here, a novel CLDN18.2 monoclonal antibody 1D5 is created with superior high specificity and affinity, and the antibody-dependent fluorescence-magnetic nanoparticle is developed for specific detection and magnetic hyperthermia (MHT). Under the assistance of sensitive fluorescence and deep-penetrating magnetic particle imaging for tracing and timing the optimal nanoparticle dosage, MHT induces robust immunogenic response via DNA mismatch repair and tumor-associated antigen release. It recruits CD11c+ dendritic cells, compensates PD-1 in CD8+ T cells, and enhances CD86+ macrophage polarization. The combination of anti-PD-1 therapy increased TNF-α and IFN-γ secretion and further boosted the cytotoxic efficacy of CD8+ T cells. Excellent therapeutic efficacy is found simultaneously on cell-derived allografts and patient-derived xenografts based on this spatiotemporally manipulated strategy, presenting a therapeutic option for enhancing responsiveness to immunotherapy for CLDN18.2-positive individuals.

Advances in engineering nanoparticles for magnetic particle imaging (MPI)

Magnetic particle imaging (MPI) is an emerging imaging modality with exciting biomedical applications, such as cell tracking, blood pool imaging, and image-guided magnetic hyperthermia. MPI is unique in that signal is generated entirely by synthetic nanoparticle tracers, motivating precise engineering of magnetic nanoparticle properties including size, shape, composition, and coating to address the needs of specific applications. However, success in many applications and in clinical transition requires development of high-sensitivity and high-resolution tracers, for which there is considerable room for improvement. This review summarizes recent advancements in MPI tracer synthesis and compares reported tracers in terms of sensitivity and resolution. In making these comparisons, we point out inconsistencies in reporting of MPI tracer properties. To overcome this challenge, we propose a list of properties to standardize characterization and reporting of new MPI tracers and improve communication within the field.

Recent Advancements in Electrochemical Sensors Based on MOFs and Their Derivatives

Metal-organic frameworks (MOFs) are composed of metal nodes and organic linkers that can self-assemble into an infinite network. The high porosity and large surface area of MOFs facilitate the effective enrichment and mass transfer of analytes, which can enhance the signal response and improve the sensitivity of electrochemical sensors. Additionally, MOFs and their derivatives possess the properties of unsaturated metal sites and tunable structures, collectively demonstrating their potential for electrochemical sensing. This paper summarizes the preparation methods, structural properties, and applications of MOFs and their derivatives in electrochemical sensing, emphasizing sensors' selectivity and sensitivity from the perspectives of direct and indirect detection. Additionally, it also explores future directions and prospects for MOFs in electrochemical sensing, with the aim of overcoming current limitations through innovative approaches.

Responsive Magnetic Particle Imaging Tracer: Overcoming "Always-On" Limitation, Eliminating Interference, and Ensuring Safety in Adaptive Therapy

Magnetic particle imaging (MPI) has emerged as a novel technology utilizing superparamagnetic nanoparticles as tracers, essential for disease diagnosis and treatment guidance in preclinical animal models. Unlike other modalities, MPI provides high sensitivity, deep tissue penetration, and no signal attenuation. However, existing MPI tracers suffer from "always-on" signals, which complicate organ-specific imaging and hinder accuracy. To overcome these challenges, we have developed a responsive MPI tracer using pH-responsive PdFe alloy particles coated with a gatekeeper polymer. This tracer exhibits pH-sensitive Fe release and modulation of the MPI signal, enabling selective imaging with a higher signal-to-noise ratio and intratumoral pH quantification. Notably, this responsive tracer facilitates subtraction-enhanced MPI imaging, effectively eliminating interference from liver uptake and expanding the scope of abdominal imaging. Additionally, the tracer employs a dual-function mechanism for adaptive cancer therapy, combining pH-switchable enzyme-like catalysis with dual-key co-activation of ROS generation, and Pd skeleton that scavenges free radicals to minimize Fe-related toxicity. This advancement promises to significantly expand MPI's applicability in diagnostics and therapeutic monitoring, marking a leap forward in imaging technology.

Peptide-Functionalized Inorganic Oxide Nanomaterials for Solid Cancer Imaging and Therapy

The diagnosis and treatment of solid tumors have undergone significant advancements marked by a trend toward increased specificity and integration of imaging and therapeutic functions. The multifaceted nature of inorganic oxide nanomaterials (IONs), which boast optical, magnetic, ultrasonic, and biochemical modulatory properties, makes them ideal building blocks for developing multifunctional nanoplatforms. A promising class of materials that have emerged in this context are peptide-functionalized inorganic oxide nanomaterials (PFIONs), which have demonstrated excellent performance in multifunctional imaging and therapy, making them potential candidates for advancing solid tumor diagnosis and treatment. Owing to the functionalities of peptides in tumor targeting, penetration, responsiveness, and therapy, well-designed PFIONs can specifically accumulate and release therapeutic or imaging agents at the solid tumor sites, enabling precise imaging and effective treatment. This review provides an overview of the recent advances in the use of PFIONs for the imaging and treatment of solid tumors, highlighting the superiority of imaging and therapeutic integration as well as synergistic treatment. Moreover, the review discusses the challenges and prospects of PFIONs in depth, aiming to promote the intersection of the interdisciplinary to facilitate their clinical translation and the development of personalized diagnostic and therapeutic systems by optimizing the material systems.

A review of metallic nanoparticles: present issues and prospects focused on the preparation methods, characterization techniques, and their theranostic applications

Metallic nanoparticles (MNPs) have garnered significant attention due to their ability to improve the therapeutic index of medications by reducing multidrug resistance and effectively delivering therapeutic agents through active targeting. In addition to drug delivery, MNPs have several medical applications, including in vitro and in vivo diagnostics, and they improve the biocompatibility of materials and nutraceuticals. MNPs have several advantages in drug delivery systems and genetic manipulation, such as improved stability and half-life in circulation, passive or active targeting into the desired target selective tissue, and gene manipulation by delivering genetic materials. The main goal of this review is to provide current information on the present issues and prospects of MNPs in drug and gene delivery systems. The current study focused on MNP preparation methods and their characterization by different techniques, their applications to targeted delivery, non-viral vectors in genetic manipulation, and challenges in clinical trial translation.

Integration of photomagnetic bimodal imaging to monitor an autogenous exosome loaded platform: unveiling strong targeted retention effects for guiding the photothermal and magnetothermal therapy in a mouse prostate cancer model

BACKGROUND

Prostate cancer (PCa) is the most prevalent cancer among males, emphasizing the critical need for precise diagnosis and treatment to enhance patient prognosis. Recent studies have extensively utilized urine exosomes from patients with cancer for targeted delivery. This study aimed to employ highly sensitive magnetic particle imaging (MPI) and fluorescence molecular imaging (FMI) to monitor the targeted delivery of an exosome-loaded platform at the tumour site, offering insights into a potential combined photothermal and magnetic thermal therapy regime for PCa.

RESULTS

MPI and FMI were utilized to monitor the in vivo retention performance of exosomes in a prostate tumour mouse model. The exosome-loaded platform exhibited robust homologous targeting ability during imaging (SPIONs@EXO-Dye:66·48%±3·85%; Dye-SPIONs: 34·57%±7·55%, **P<0·01), as verified by in vitro imaging and in vitro tissue Prussian blue staining.

CONCLUSIONS

The experimental data underscore the feasibility of using MPI for in vivo PCa imaging. Furthermore, the exosome-loaded platform may contribute to the precise diagnosis and treatment of PCa.

Enzyme-loaded manganese-porphyrin metal-organic nanoframeworks for oxygen-evolving photodynamic therapy of hypoxic cells

Photodynamic therapy (PDT) is attracting great attention for cancer treatments, while its therapeutic efficacy is limited by unsatisfactory photosensitizers and hypoxic tumor microenvironment (TME). To address these problems, we have developed catalase-loaded manganese-porphyrin frameworks (CAT@MnPFs) for catalytically-assisted PDT of cancer cells. CAT@MnPFs were constructed by the assembly of Mn2+ ions and PpIX into MnPFs and the subsequent loading of catalase. Under 650 nm light irradiation, the porphyrin (Protoporphyrin IX) within the structure of CAT@MnPFs can convert oxygen (O2) into singlet oxygen (1O2), showing the photodynamic effect. Importantly, the loaded catalase can decompose hydrogen peroxide (H2O2) into O2 with a huge elevation of O2 level (13.22 mg L-1) in 600 s, thus promoting 1O2 generation via PDT. As a result, CAT@MnPFs combined with 650 nm light can effectively ablate cancer cells due to the catalase-assisted oxygen-evolving PDT, showing a high therapeutic efficacy. Meanwhile, after the incubation with CAT@MnPFs, unobvious damage can be found in normal and red blood cells. Thus, the obtained CAT@MnPFs integrate the advantage of photosensitizers and catalase for oxygen-evolving PDT, which can provide some insight for treating hypoxic cells.

Multifaceted Carbonized Metal-Organic Frameworks Synergize with Immune Checkpoint Inhibitors for Precision and Augmented Cuproptosis Cancer Therapy

The discovery of cuproptosis, a copper-dependent mechanism of programmed cell death, has provided a way for cancer treatment. However, cuproptosis has inherent limitations, including potential cellular harm, the lack of targeting, and insufficient efficacy as a standalone treatment. Therefore, exogenously controlled combination treatments have emerged as key strategies for cuproptosis-based oncotherapy. In this study, a Cu2-xSe@cMOF nanoplatform was constructed for combined sonodynamic/cuproptosis/gas therapy. This platform enabled precise cancer cotreatment, with external control allowing the selective induction of cuproptosis in cancer cells. This approach effectively prevented cancer metastasis and recurrence. Furthermore, Cu2-xSe@cMOF was combined with the antiprogrammed cell death protein ligand-1 antibody (aPD-L1), and this combination maximized the advantages of cuproptosis and immune checkpoint therapy. Additionally, under ultrasound irradiation, the H2Se gas generated from Cu2-xSe@cMOF induced cytotoxicity in cancer cells. Further, it generated reactive oxygen species, which hindered cell survival and proliferation. This study reports an externally controlled system for cuproptosis induction that combines a carbonized metal-organic framework with aPD-L1 to enhance cancer treatment. This precision and reinforced cuproptosis cancer therapy platform could be valuable as an effective therapeutic agent to reduce cancer mortality and morbidity in the future.

Magnetic Particle Imaging: From Tracer Design to Biomedical Applications in Vasculature Abnormality

Magnetic particle imaging (MPI) is an emerging non-invasive tomographic technique based on the response of magnetic nanoparticles (MNPs) to oscillating drive fields at the center of a static magnetic gradient. In contrast to magnetic resonance imaging (MRI), which is driven by uniform magnetic fields and projects the anatomic information of the subjects, MPI directly tracks and quantifies MNPs in vivo without background signals. Moreover, it does not require radioactive tracers and has no limitations on imaging depth. This article first introduces the basic principles of MPI and important features of MNPs for imaging sensitivity, spatial resolution, and targeted biodistribution. The latest research aiming to optimize the performance of MPI tracers is reviewed based on their material composition, physical properties, and surface modifications. While the unique advantages of MPI have led to a series of promising biomedical applications, recent development of MPI in investigating vascular abnormalities in cardiovascular and cerebrovascular systems, and cancer are also discussed. Finally, recent progress and challenges in the clinical translation of MPI are discussed to provide possible directions for future research and development.

Recent advances in functionalized ferrite nanoparticles: From fundamentals to magnetic hyperthermia cancer therapy

Cancers are fatal diseases that lead to most death of human beings, which urgently require effective treatments methods. Hyperthermia therapy employs magnetic nanoparticles (MNPs) as heating medium under external alternating magnetic field. Among various MNPs, ferrite nanoparticles (FNPs) have gained significant attention for hyperthermia therapy due to their exceptional magnetic properties, high stability, favorable biological compatibility, and low toxicity. The utilization of FNPs holds immense potential for enhancing the effectiveness of hyperthermia therapy. The main hurdle for hyperthermia treatment includes optimizing the heat generation capacity of FNPs and controlling the local temperature of tumor region. This review aims to comprehensively evaluate the magnetic hyperthermia treatment (MHT) of FNPs, which is accomplished by elucidating the underlying mechanism of heat generation and identifying influential factors. Based upon fundamental understanding of hyperthermia of FNPs, valuable insights will be provided for developing efficient nanoplatforms with enhanced accuracy and magnetothermal properties. Additionally, we will also survey current research focuses on modulating FNPs' properties, external conditions for MHT, novel technical methods, and recent clinical findings. Finally, current challenges in MHT with FNPs will be discussed while prospecting future directions.

Shape Anisotropy-Governed High-Performance Nanomagnetosol for In Vivo Magnetic Particle Imaging of Lungs

Caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), coronavirus disease 2019 (COVID-19) has shown extensive lung manifestations in vulnerable individuals, putting lung imaging and monitoring at the forefront of early detection and treatment. Magnetic particle imaging (MPI) is an imaging modality, which can bring excellent contrast, sensitivity, and signal-to-noise ratios to lung imaging for the development of new theranostic approaches for respiratory diseases. Advances in MPI tracers would offer additional improvements and increase the potential for clinical translation of MPI. Here, a high-performance nanotracer based on shape anisotropy of magnetic nanoparticles is developed and its use in MPI imaging of the lung is demonstrated. Shape anisotropy proves to be a critical parameter for increasing signal intensity and resolution and exceeding those properties of conventional spherical nanoparticles. The 0D nanoparticles exhibit a 2-fold increase, while the 1D nanorods have a > 5-fold increase in signal intensity when compared to VivoTrax. Newly designed 1D nanorods displayed high signal intensities and excellent resolution in lung images. A spatiotemporal lung imaging study in mice revealed that this tracer offers new opportunities for monitoring disease and guiding intervention.

Post-synthesis Oxidation of Superparamagnetic Iron Oxide Nanoparticles to Enhance Magnetic Particle Imaging Performance

This study investigates the impact of post-synthesis oxidation on the performance of superparamagnetic iron oxide nanoparticles (SPIONs) in magnetic particle imaging (MPI), an emerging technology with applications in diagnostic imaging and theranostics. SPIONs synthesized from iron oleate were subjected to a post-synthesis oxidation treatment with a 1% Oxygen in Argon mixture. MPI performance, gauged via signal intensity and resolution using a MOMENTUM™ scanner, was correlated to the nanoparticles' physical and magnetic properties. Post-synthesis oxidation did not alter physical attributes like size and shape, but significantly enhanced magnetic properties. Saturation magnetization increased from 52% to 93% of the bulk value for magnetite, leading to better MPI performance in terms of signal intensity and resolution. However, the observed MPI performance did not fully align with predictions based on the ideal Langevin model, indicating the need for considering factors like relaxation and shape anisotropy. The findings underscore the potential of post-synthesis oxidation as a method to fine-tune magnetic properties of SPIONs and improve MPI performance, and the need for reproducible synthesis methods that afford finely tuned control of nanoparticle size, shape, and magnetic properties.

Zn-Shik-PEG nanoparticles alleviate inflammation and multi-organ damage in sepsis

Sepsis is defined as a life-threatening organ dysfunction caused by excessive formation of reactive oxygen species (ROS) and dysregulated inflammatory response. Previous studies have reported that shikonin (Shik) possess prominent anti-inflammatory and antioxidant effects and holds promise as a potential therapeutic drug for sepsis. However, the poor water solubility and the relatively high toxicity of shikonin hamper its clinical application. To address this challenge, we constructed Zn2+-shikonin nanoparticles, hereafter Zn-Shik-PEG NPs, based on an organic-inorganic hybridization strategy of metal-polyphenol coordination to improve the aqueous solubility and biosafety of shikonin. Mechanistic studies suggest that Zn-Shik-PEG NPs could effectively clear intracellular ROS via regulating the Nrf2/HO-1 pathway, meanwhile Zn-Shik-PEG NPs could inhibit NLRP3 inflammasome-mediated activation of inflammation and apoptosis by regulating the AMPK/SIRT1 pathway. As a result, the Zn-Shik-PEG NPs demonstrated excellent therapeutic efficacies in lipopolysaccharide (LPS) as well as cecal ligation puncture (CLP) induced sepsis model. These findings suggest that Zn-Shik-PEG NPs may have therapeutic potential for the treatment of other ROS-associated and inflammatory diseases.

Improved Quantitative Analysis Method for Magnetic Particle Imaging Based on Deblurring and Region Scalable Fitting

PURPOSE

Magnetic particle imaging (MPI) is a technique for imaging magnetic particle concentration distribution. It has the advantages of high sensitivity, no signal attenuation with depth, and no ionizing radiation. Although MPI has been widely used in the biomedical field, accurate image analysis has been challenging due to its anisotropic point spread function (PSF). The purpose of this study is to propose an MPI image restoring and segmentation method to facilitate a more precise quantitative evaluation of the magnetic particle imaging in vivo.

PROCEDURES

We proposed a DeRSF method that combined deblurring and region scalable fitting (RSF) to determine the imaging tracer distribution. Then a uniform erosion and scaling criterion was established based on simulation experiments to correct the segmentation results, which was further validated on phantom imaging. Finally, we imaged the MPI tracer at gradient concentrations to establish the calibration curve between the MPI signal and iron mass for iron quantification in phantom and in vivo imaging.

RESULTS

The phantom imaging experiments showed that our method achieved improved segmentation performance. The mean value of the dice coefficients for segmentation was up to 0.86, demonstrating that our method can accurately map and quantify the distribution of the tracer. Moreover, the iron quantification on both phantom and in vivo mouse imaging was realized with the minimal error of 5.50%, by our established calibration curve.

CONCLUSIONS

Our proposed DeRSF method was successfully used for improved MPI quantitative analysis. More importantly, this method also showed accurate quantitative results on images with different shapes and tracer concentrations in both phantom and in vivo data, which laid the foundation for the biomedical study of MPI.

Catalytically Active Metal-Organic Frameworks Elicit Robust Immune Response to Combination Chemodynamic and Checkpoint Blockade Immunotherapy

Chemodynamic therapy (CDT) strategies rely on the generation of reactive oxygen species (ROS) to kill tumor cells, with hydroxyl radicals (^•OH) serving as the key mediators of cytotoxicity in this setting. However, the efficacy of CDT approaches is often hampered by the properties of the tumor microenvironment (TME) and associated limitations to the Fenton reaction that constrains ROS generation. As such, there is a pressing need for the design of new nanoplatforms capable of improving CDT outcomes. In this study, an Fc-based metal-organic framework (MOF) vitamin k3 (Vk3)-loaded cascade catalytic nanoplatform (Vk3@Co-Fc) was developed. This platform was capable of undergoing TME-responsive degradation without impacting normal cells. After its release, Vk3 was processed by nicotinamide adenine dinucleotide hydrogen phosphate (NAD(P)H) quinone oxidoreductase-1 (NQO1), which is highly expressed in tumor cells, thereby yielding large quantities of H₂O₂ that in turn interact with Fe ions via the Fenton reaction to facilitate in situ cytotoxic ^•OH production. This process leads to immunogenic cell death (ICD) of the tumor, which then promotes dendritic cell maturation and ultimately increases T cell infiltration into the tumor site. When this nanoplatform was combined with programmed death 1 (PD-1) checkpoint blockade approaches, it was sufficient to enhance tumor-associated immune responses in breast cancer as evidenced by increases in the frequencies of CD45⁺ leukocytes and CD8⁺ cytotoxic T lymphocytes, thereby inhibiting tumor metastasis to the lungs and improving murine survival outcomes. Together, this Vk3@Co-Fc cascading catalytic nanoplatform enables potent cancer immunotherapy for breast cancer regression and metastasis prevention.

A guide to the design of magnetic particle imaging tracers for biomedical applications

Magnetic Particle Imaging (MPI) is a novel and emerging non-invasive technique that promises to deliver high quality images, no radiation, high depth penetration and nearly no background from tissues. Signal intensity and spatial resolution in MPI are heavily dependent on the properties of tracers. Hence the selection of these nanoparticles for various applications in MPI must be carefully considered to achieve optimum results. In this review, we will provide an overview of the principle of MPI and the key criteria that are required for tracers in order to generate the best signals. Nanoparticle materials such as magnetite, metal ferrites, maghemite, zero valent iron@iron oxide core@shell, iron carbide and iron-cobalt alloy nanoparticles will be discussed as well as their synthetic pathways. Since surface modifications play an important role in enabling the use of these tracers for biomedical applications, coating options including the transfer from organic to inorganic media will also be discussed. Finally, we will discuss different biomedical applications and provide our insights into the most suitable tracer for each of these applications.

Surface oxygen vacancies and carbon dopant co-decorated magnetic ZnFe2O4 as photo-Fenton catalyst towards efficient degradation of tetracycline hydrochloride

Carbon doped strategy has been recognized as an efficient strategy to enhance photo-Fenton degradation performance. However, the preparation of high efficiency C-doped photocatalyst has been a significant challenge. Herein, we synthesized magnetic carbon-doped ZnFe₂O₄ via a facile solvothermal-calcination route. The photo-Fenton activity of C-doped ZnFe₂O₄ under visible light (λ > 420 nm) was evaluated by degradation of tetracycline hydrochloride. C-doped sample, CZF-2 (0.5 g L^-1) presented excellent removal performance for TC-HCl (20 mg L^-1) in presence of H₂O₂ (10 mM) and could remove 90.8% of TC-HCl within 50 min. The C-doping modulates crystal defects and generates surface oxygen vacancies simultaneously, thus building a new C-doping level near valence band and a defect level under the conduction band. Meanwhile, surface oxygen vacancies bring photo-generated electrons and electrons generated from itself to surface to accelerate photo-Fenton reaction, and the holes are rapidly transferred to the surface to participate in the degradation of pollutants.

Optical magnetic multimodality imaging of plectin-1-targeted imaging agent for the precise detection of orthotopic pancreatic ductal adenocarcinoma in mice

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy worldwide, and the precise detection is challenging currently. Magnetic particle imaging (MPI) is suitable for imaging deep and internal PDAC tumours because of its high sensitivity and unlimited imaging depth. The purpose of this study was to utilize the MPI, in combination with fluorescence molecular imaging (FMI) and magnetic resonance imaging (MRI), to advance the in vivo precise detection of PDAC xenografts.

METHODS

The PDAC targeted plectin-1 peptide and IRDye800CW were conjugated to the superparamagnetic iron oxide nanoparticles (PTP-Fe3O4-IRDye800CW) for the PDAC-targeting triple-modality imaging. Subcutaneous and orthotopic PDAC mouse models were established. FMI, MPI, and MRI were performed for dynamic and quantitative observation of PDAC tumours. Histological staining analyses were used for ex vivo validation.

FINDINGS

PTP-Fe3O4-IRDye800CW nanoparticles possessed great triple-modality imaging performance and specific targeting to plectin-1 expressed on PDAC cells. For in vivo multi-modality imaging of orthotopic PDAC models, the PTP-Fe3O4-IRDye800CW nanoparticles demonstrated higher specificity, even distribution, and longer retention effects in tumours for over 7 d compared with Con-Fe3O4-IRDye800CW nanoparticles. (MPI, 2d post-injection: PTP-Fe3O4-IRDye800CW: 85.72% ± 1.53% vs. Con-Fe3O4-IRDye800CW: 74.41% ± 1.91%, **P < 0.01 (Student's t test)). Ex vivo histological and Prussian blue stainings were performed to validate the distribution of probes.

INTERPRETATION

These data demonstrate the feasibility of utilizing MPI for in vivo PDAC imaging and complement with FMI/MRI for a precise and comprehensive in vivo characterization of PDAC. This may benefit PDAC patients for precise diagnosis and guidance of therapy.

FUNDING

This study was funded by the National Natural Science Foundation of China (Grant No. 62027901, 82071896, 81871422, 81871514, 81227901), Ministry of Science and Technology of China under Grant No. 2017YFA0205200, 2017YFA0700401, Beijing Natural Science Foundation (Grant No. 7212207), Elite Program of Dong Cheng District of Beijing (2020-dchrcpyzz-28), and Peking University Third Hospital (BYSYZD2019018, and jyzc2018-02).

Magnetic particle imaging: tracer development and the biomedical applications of a radiation-free, sensitive, and quantitative imaging modality

Magnetic particle imaging (MPI) is an emerging tracer-based modality that enables real-time three-dimensional imaging of the non-linear magnetisation produced by superparamagnetic iron oxide nanoparticles (SPIONs), in the presence of an external oscillating magnetic field. As a technique, it produces highly sensitive radiation-free tomographic images with absolute quantitation. Coupled with a high contrast, as well as zero signal attenuation at-depth, there are essentially no limitations to where that can be imaged within the body. These characteristics enable various biomedical applications of clinical interest. In the opening sections of this review, the principles of image generation are introduced, along with a detailed comparison of the fundamental properties of this technique with other common imaging modalities. The main feature is a presentation on the up-to-date literature for the development of SPIONs tailored for improved imaging performance, and developments in the current and promising biomedical applications of this emerging technique, with a specific focus on theranostics, cell tracking and perfusion imaging. Finally, we will discuss recent progress in the clinical translation of MPI. As signal detection in MPI is almost entirely dependent on the properties of the SPION employed, this work emphasises the importance of tailoring the synthetic process to produce SPIONs demonstrating specific properties and how this impacts imaging in particular applications and MPI's overall performance.

Metal-Organic Framework (MOF)-Based Ultrasound-Responsive Dual-Sonosensitizer Nanoplatform for Hypoxic Cancer Therapy

Sonodynamic therapy (SDT), which uses reactive oxygen species to target tumors, has shown promise in the management of unresectable cancers. However, the hypoxic tumor environment limits SDT efficiency, making complete tumor destruction challenging. Here, a dual-sonosensitizer nanoplatform is developed by loading an alkyl radical generator (2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, AIPH) onto a zirconium metal-organic framework (Zr-MOF). The Zr-MOF@AIPH nanoparticles (NPs) can produce singlet oxygen, which can kill tumor cells under normoxic conditions, as well as alkyl radicals, which can kill tumor cells under both normoxic and hypoxic conditions. The combination of these free radicals further enhances SDT efficiency. Meanwhile, the nitrogen generated owing to AIPH decomposition can reduce the cavitation threshold and enhance the acoustic cavitation effect, thereby promoting NP penetration at the tumor site. Moreover, Zr-MOF@AIPH NPs exhibit good photoacoustic, fluorescence, and ultrasound imaging abilities due to their porphyrin-based structure and the nitrogen generated, which can remotely control NP delivery and determine the optimal therapeutic time window, ensuring the maximization of SDT efficiency. In vitro and in vivo examinations prove the superior antitumor efficacy, excellent biocompatibility, and favorable imaging ability of Zr-MOF@AIPH. This study spearheads the charge toward improving SDT efficacy in hypoxic environments via a combination of complementary sonosensitizers.

Transition metal ion-doped ferrites nanoparticles for bioimaging and cancer therapy

Magnetic nanoparticles (MNPs) have been extensively researched and implemented in biomedicine for more than half a century due to their non-invasive nature, ease of temporal and spatial manipulation, and considerable biocompatibility. However, the complex magnetic behaviour of MNPs is influenced by several parameters (e.g., particle size, shape, composition, core-shell structure, etc.), among which the amount of transition metal doping plays an important factor. For this reason, the doping of ferrite with transition metals has been used as an effective strategy to precisely tailor MNPs to achieve satisfactory performance in biomedical applications. In this review, we first introduced the main properties of coordinated MNPs (including magnetic moment and saturated magnetisation) and provide a comprehensive overview of the mechanistic studies related to the doping of transition metal ions into ferrite to precisely modulate its magnetic properties. We also highlighted the potential mechanisms and recent advances in transition metal ion-doped MNPs (TMNPs) for bioimaging (magnetic resonance imaging and magnetic particle imaging) and tumour therapy (e.g., magneto-mechanical killing, magnetothermal therapy, and drug delivery). Finally, we summarised the current challenges and future trends of TMNPs in the biomedical field based on the latest advances by researchers.

Nanoscale covalent organic frameworks: from controlled synthesis to cancer therapy

Covalent organic frameworks (COFs), as a new type of crystalline porous materials, mainly consist of light-weight elements (H, B, C, N and O) linked by dynamic covalent bonds to form periodical structures of two or three dimensions. As an attribute of their low density, large surface area, and excellent adjustable pore size, COFs show great potential in many fields including energy storage and separation, catalysis, sensing, and biomedicine. However, compared with metal organic frameworks (MOFs), the relatively large size and irregular morphology of COFs affect their biocompatibility and bioavailability in vivo, thus impeding their further biomedical applications. This Review focuses on the controlled design strategies of nanoscale COFs (NCOFs), unique properties of NCOFs for biomedical applications, and recent progress in NCOFs for cancer therapy. In addition, current challenges for the biomedical use of NCOFs and perspectives for further improvements are presented.

Hypoxia-Adapted Sono-chemodynamic Treatment of Orthotopic Pancreatic Carcinoma Using Copper Metal-Organic Frameworks Loaded with an Ultrasound-Induced Free Radical Initiator

The efficacy of sonodynamic therapy (SDT) is largely dependent upon oxygen availability to generate deleterious reactive oxygen species, and as such, hypoxic microenvironments greatly constrain the efficacy of SDT. Development of free radical generators that are not dependent on oxygen and related combination treatment strategies thus have the potential to enhance the antitumor potential of SDT. Combined treatment strategies are expected to improve the efficacy of sonodynamic antitumor therapy. As metal-organic framework (MOF) platforms are highly amenable to integration with other therapeutic approaches, we herein report the development of tumor microenvironment (TME)-responsive nanoparticles constructed by embedding the azo initiator 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (AIPH) into hypoxia-triggered copper metal-organic framework (Cu-MOF) nanovectors to achieve synergistic sono-chemodynamic therapy in an orthotopic murine pancreatic carcinoma model system. When exposed to hypoxic conditions within the TME, this Cu-MOF structure underwent degradation, leading to the release of Cu2+ and AIPH. Cu2+ was then able to deplete local glutathione stores, resulting in the reduction of Cu2+ to Cu+, which then reacts with endogenous H2O2 in a Fenton-like reaction to yield cytotoxic hydroxyl radicals (•OH) for chemodynamic therapy. When exposed to ultrasound irradiation, AIPH further degraded in an oxygen-independent manner to yield nitrogen bubbles and alkyl radicals, the former of which enhanced the ability of these nanoparticles to penetrate deeply into the tumor. The resultant radicals induced substantial DNA damage and apoptotic cell death within target tumors under different levels of oxygen availability. As such, this hypoxic TME-responsive synergistic sono-chemodynamic approach offers an ideal means of achieving oxygen-independent free radical generation and enhanced treatment efficacy.