Manganese Oxide Nanomaterials: Synthesis, Properties, and Theranostic Applications

Modulating residual ammonium in MnO2 for high-rate aqueous zinc-ion batteries

Manganese dioxide (MnO₂), as a promising cathode candidate, has attracted great attention in aqueous zinc ion batteries (ZIBs). However, the undesirable dissolution of Mn²⁺ and the sluggish kinetic reaction are still two challenges to overcome before achieving good cycling stability and high-rate performance of ZIBs. Herein, β-MnO₂ with chemically residual NH₄⁺ (NMO) was successfully fabricated by controlling the washing condition and utilized as a cathode in a ZIB. Interestingly, NH₄⁺, as a layer pillar in the tunnel structure of NMO, could enhance its conductivity by changing the chemical structure, contributing to accelerating the kinetics of the charge carrier. Moreover, the residual NH₄⁺ in NMO could stabilize the chemical microstructure through the cationic electrostatic shielding effect and the formation of Mn-O⋯H bonds in NMO, promoting the reversible and successive insertion/extraction of H⁺/Zn²⁺ in the ZIB. As a result, the Zn/NMO battery exhibits excellent rate performance (up to 8.0 A g^-1) and cycling stability (10 000 cycles). This work will pave the way for the design of cathode materials with nonmetallic doping for high-performance ZIB systems.

Nanozymes-recent development and biomedical applications

Nanozyme is a series of nanomaterials with enzyme-mimetic activities that can proceed with the catalytic reactions of natural enzymes. In the field of biomedicine, nanozymes are capturing tremendous attention due to their high stability and low cost. Enzyme-mimetic activities of nanozymes can be regulated by multiple factors, such as the chemical state of metal ion, pH, hydrogen peroxide (H₂O₂), and glutathione (GSH) level, presenting great promise for biomedical applications. Over the past decade, multi-functional nanozymes have been developed for various biomedical applications. To promote the understandings of nanozymes and the development of novel and multifunctional nanozymes, we herein provide a comprehensive review of the nanozymes and their applications in the biomedical field. Nanozymes with versatile enzyme-like properties are briefly overviewed, and their mechanism and application are discussed to provide understandings for future research. Finally, underlying challenges and prospects of nanozymes in the biomedical frontier are discussed in this review.

Recent Advance of Nanomaterial-Mediated Tumor Therapies in the Past Five Years

Cancer has posed a major threat to human life and health with a rapidly increasing number of patients. The complexity and refractory of tumors have brought great challenges to tumor treatment. In recent years, nanomaterials and nanotechnology have attracted more attention and greatly improved the efficiency of tumor therapies and significantly prolonged the survival period, whether for traditional tumor treatment methods such as radiotherapy, or emerging methods, such as phototherapy and immunotherapy, sonodynamic therapy, chemodynamic therapy and RNA interference therapeutics. Various monotherapies have obtained positive results, while combination therapies are further proposed to prevent incomplete eradication and recurrence of tumors, strengthen tumor killing efficacy with minimal side effects. In view of the complementary promotion effects between different therapies, it is vital to utilize nanomaterials as the link between monotherapies to achieve synergistic performance. Further development of nanomaterials with efficient tumor-killing effect and better biosafety is more in line with the needs of clinical treatment. In a word, the development of nanomaterials provides a promising way for tumor treatment, and here we will review the emerging nanomaterials towards radiotherapy, phototherapy and immunotherapy, and summarized the developed nanocarriers applied for the tumor combination therapies in the past 5 years, besides, the advances of some other novel therapies such as sonodynamic therapy, chemodynamic therapy, and RNA interference therapeutics have also been mentioned.

Construction of iron-mineralized black phosphorene nanosheet to combinate chemodynamic therapy and photothermal therapy

Chemodynamic therapy (CDT) by triggering Fenton reaction or Fenton-like reaction to generate hazardous hydroxyl radical (•OH), is a promising strategy to selectively inhibit tumors with higher H₂O₂ levels and relatively acidic microenvironment. Current Fe-based Fenton nanocatalysts mostly depend on slowly releasing iron ions from Fe or Fe oxide-based nanoparticles, which leads to a limited rate of Fenton reaction. Herein, we employed black phosphorene nanosheets (BPNS), a biocompatible and biodegradable photothermal material, to develop iron-mineralized black phosphorene nanosheet (BPFe) by in situ deposition method for chemodynamic and photothermal combination cancer therapy. This study demonstrated that the BPFe could selectively increase cytotoxic ·OH in tumor cells whereas having no influence on normal cells. The IC₅₀ of BPFe for tested tumor cells was about 3–6 μg/mL, which was at least one order of magnitude lower than previous Fe-based Fenton nanocatalysts. The low H₂O₂ level in normal mammalian cells guaranteed the rare cytotoxicity of BPFe. Moreover, the combination of photothermal therapy (PTT) with CDT based on BPFe was proved to kill tumors more potently with spatiotemporal accuracy, which exhibited excellent anti-tumor effects in xenografted MCF-7 tumor mice models.

Self-sustained recovery of silver with stainless-steel based Cobalt/Molybdenum/Manganese polycrystalline catalytic electrode in bio-electroreduction microbial fuel cell (BEMFC)

In this study, a novel bio-electroreduction microbial fuel cell (BEMFC) assisted by stainless-steel based Cobalt/Molybdenum/Manganese (Co/Mo/Mn-SS) polycrystalline catalytic electrode was used to achieve high recovery to silver. The exoelectrogens (Shewanella sp. etc.) using organic wastewater (the inflow was controlled at 1.2 L d^-1) as nutrient matrix in the anode chamber generated electrons, while silver ions were simultaneously electroreduced and electrodeposited on the surface of the catalytic electrode as electron acceptors. Silver nanoplates could be observed directly. The products of electroreduction on the cathode were analyzed by Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffractometer (XRD), and the results of electrochemical characterization confirmed the existence of silver in the products. In the operation, the silver ions were in-situ recovered and enriched from the initial concentration of 20-300 mg L^-1 to almost complete recovery (8-18 h), with the maximum power density of 1008.2 mW m^-2 and 5.5 A m^-2 current density. The recovery efficiency of silver in the BEMFC using the Co/Mo/Mn-SS electrode was up to 9.60 kg m^-2h^-1, and the energy efficiency was 27.8 kg kWh^-1. Under the continuous flow operation mode, the BEMFC still achieved 90.2% recovery efficiency of the silver.

Manganese oxide nanomaterials for bacterial infection detection and therapy

Bacterial infection has received substantial attention and poses a serious threat to human health. Although antibiotics can effectively fight against bacterial infection, the occurrence of antibiotic resistance has become increasingly serious in recent years, which tremendously hinders its clinical application. Consequently, it is urgent to explore novel strategies to achieve efficacious treatment of bacterial diagnosis and detection. Manganese dioxide (MnO₂) nanomaterial has been extensively reported in tumor therapy. Nevertheless, there are few antibacterial reviews of MnO₂. Herein, we will discuss the applications of MnO₂ in the detection and treatment of bacterial infection, including photodynamic therapy, immunotherapy, improvement of hypoxia, dual-modal combination therapy, reactive oxygen species scavenging, magnetic resonance imaging, optical application of acoustic imaging, and so forth. This review is expected to provide meaningful guidance on further research of MnO₂ nanomaterial for antibacterial applications.

Hydrogen Sulfide: An Emerging Precision Strategy for Gas Therapy

Advances in nanotechnology have enabled the rapid development of stimuli-responsive therapeutic nanomaterials for precision gas therapy. Hydrogen sulfide (H₂ S) is a significant gaseous signaling molecule with intrinsic biochemical properties, which exerts its various physiological effects under both normal and pathological conditions. Various nanomaterials with H₂ S-responsive properties, as new-generation therapeutic agents, are explored to guide therapeutic behaviors in biological milieu. The cross disciplinary of H₂ S is an emerging scientific hotspot that studies the chemical properties, biological mechanisms, and therapeutic effects of H₂ S. This review summarizes the state-of-art research on H₂ S-related nanomedicines. In particular, recent advances in H₂ S therapeutics for cancer, such as H₂ S-mediated gas therapy and H₂ S-related synergistic therapies (combined with chemotherapy, photodynamic therapy, photothermal therapy, and chemodynamic therapy) are highlighted. Versatile imaging techniques for real-time monitoring H₂ S during biological diagnosis are reviewed. Finally, the biosafety issues, current challenges, and potential possibilities in the evolution of H₂ S-based therapy that facilitate clinical translation to patients are discussed.

Zwitterion-Coated Ultrasmall MnO Nanoparticles Enable Highly Sensitive T1-Weighted Contrast-Enhanced Brain Imaging

Manganese oxide nanoparticles (NPs) have attracted increasing attention recently as contrast agents (CAs) for magnetic resonance imaging (MRI). However, the clinical translation and popularization of conventional MnO NPs are hampered by their relatively poor imaging performance. Herein, we report the construction of ultrasmall MnO NPs (USMnO) via a one-pot synthetic approach that show a much better capability of T1-weighted contrast enhancement for MRI (r1 = 15.6 ± 0.4 mM-1 s-1 at 0.5 T) than MnCl2 and conventional large-sized MnO NPs (MnO-22). These USMnO are further coated with zwitterionic dopamine sulfonate (ZDS) molecules, which improves their biocompatibility and prevents nonspecific binding of serum albumins. Interestingly, USMnO@ZDS are capable of passing through the blood-brain barrier (BBB), which enables the acquisition of clear images showing brain anatomic structures with T1-weighted contrast-enhanced MRI. Therefore, our USMnO@ZDS could be used as a promising MRI CA for the flexible and accurate diagnosis of brain diseases, which is also instructive for the construction of manganese-based CA with a high MRI performance.

Biomineralization-inspired synthesis of amorphous manganese phosphates for GLUT5-targeted drug-free catalytic therapy of osteosarcoma

Osteosarcoma, occurring most frequently in children, teens, and young adults, is a lethal bone cancer with a high incidence of distant metastases and drug resistance. Developing a therapeutic platform that integrates targeting, curing and imaging is highly desirable for enhanced osteosarcoma therapy, yet quite challenging. In this work, we demonstrate a novel biomineralization-inspired strategy for the synthesis of a fructose incorporated manganese phosphate (Fru-MnP) nanoplatform for tumour targeting, drug-free therapy, and MRI imaging. Benefitting from the glucose transporter 5 (GLUT5)-mediated endocytosis, our Fru-MnP nanoplatform produces a high level of reactive oxygen species (ROS) via the Mn²⁺-driven Fenton reaction within osteosarcoma cells, leading to efficient cancer cell killing due to caspase-mediated apoptosis. By virtue of the T1 signal enhancement of Mn²⁺, our Fru-MnP nanoplatform also acts as an effective tumour-specific MRI contrast agent, realizing the MRI-monitored chemodynamic therapy. The proposed synergistic therapeutic platform opens new possibilities for high efficacy therapy for osteosarcoma.

Multifunctional inorganic nanomaterials for cancer photoimmunotherapy

Phototherapy and immunotherapy in combination is regarded as the ideal therapeutic modality to treat both primary and metastatic tumors. Immunotherapy uses different immunological approaches to stimulate the immune system to identify tumor cells for targeted elimination. Phototherapy destroys the primary tumors by light irradiation, which induces a series of immune responses through triggering immunogenic cancer cell death. Therefore, when integrating immunotherapy with phototherapy, a novel anti-cancer strategy called photoimmunotherapy (PIT) is emerging. This synergistic treatment modality can not only enhance the effectiveness of both therapies but also overcome their inherent limitations, opening a new era for the current anti-cancer therapy. Recently, the advancement of nanomaterials affords a platform for PIT. From all these nanomaterials, inorganic nanomaterials stand out as ideal mediators in PIT due to their unique physiochemical properties. Inorganic nanomaterials can not only serve as carriers to transport immunomodulatory agents in immunotherapy owing to their excellent drug-loading capacity but also function as photothermal agents or photosensitizers in phototherapy because of their great optical characteristics. In this review, the recent advances of multifunctional inorganic nanomaterial-mediated drug delivery and their contributions to cancer PIT will be highlighted.

Atomically dispersed Ag on δ-MnO2via cation vacancy trapping for toluene catalytic oxidation

Atomic dispersion of Ag on δ-MnO2 was achieved via H2O2-induced Mn vacancy trapping. Single-atom Ag could activate adjacent lattice oxygen, facilitating methyl oxidation and benzene ring cleavage to improve toluene oxidation activity.

A novel CuCoS nanozyme for synergistic photothermal and chemodynamic therapy of tumors

Multifunctional CuCoS nanoparticles with photothermal converters and dual enzymatic activities have been designed for the synergistic photothermal and chemodynamic therapy of tumors.

Silencing of Pyruvate Kinase M2 via a Metal-Organic Framework Based Theranostic Gene Nanomedicine for Triple-Negative Breast Cancer Therapy

Triple-negative breast cancer (TNBC) is typically associated with poor prognosis due to its only partial response to chemotherapy and lack of clinically established targeted therapies coupled with an aggressive disease course. Aerobic glycolysis is a hallmark of reprogrammed metabolic activity in cancer cells, which can be repressed by small-interfering RNA (siRNA). However, the lack of effective carriers to deliver vulnerable siRNA restricts the clinical potentials of glycolysis-based gene therapy for TNBC. Herein, we develop a tumor-targeted, biomimetic manganese dioxide (MnO₂)-shrouded metal-organic framework (MOF) based nanomedicine to deliver siRNA against pyruvate kinase muscle isozyme M2 (siPKM2), wherein PKM2 is a rate-limiting enzyme in glycolysis, to inhibit the reprogrammed glycolysis of TNBC. This MOF-based genetic nanomedicine shows excellent monodispersity and stability and protects siPKM2 against degradation by nucleases. The nanomedicine not only substantially blocks the glycolytic pathway but also improves intracellular hypoxia in TNBC cells, with a resultant O₂-enhanced anticancer effect. In the mice orthotopic TNBC model, the nanomedicine shows a remarkable therapeutic effect. Meanwhile, the Mn²⁺ ions released from acid microenvironment-responsive MnO₂ enable in vivo monitoring of the therapeutic process with magnetic resonance imaging (MRI). Our study shows great promise with this MRI-visible MOF-based nanomedicine for treating TNBC by inhibition of glycolysis via the RNA interference.

Thermosensitive hydrogel-functionalized gold nanorod/mesoporous MnO2 nanoparticles for tumor cell-triggered drug delivery

MnO₂ owns distinct redox, imaging, and degradable properties corresponding to the tumor microenvironment. However, the onefold structure and non-modifiable property cause many obstacles to anticancer applications. In this report, we first prepared a typical core-shell gold nanorod (GNR)/manganese dioxide (MnO₂) nanoparticles (GNR/MnO₂ NPs). Interestingly, the MnO₂ had a mesoporous channel and modifiable hydroxyl group (OH). Here, the unique 'OH' groups were modified and further grafted with poly(N-isopropylacrylamide-co-acrylic acid) (PNA). As a dual-sensitive hydrogel, it was selected as the thermal/pH-sensitive component in the hybrid nanoparticles (GNR/MnO₂/PNA NPs). The anticancer drug doxorubicin hydrochloride (DOX) was selected and loaded into the hybrid nanoparticles (GNR/MnO₂/PNA-DOX NPs). The GNR/MnO₂/PNA NPs achieved satisfying drug-loading efficiency and glutathione (GSH)/pH/thermal-responsive drug-controlled release. As a side benefit, the GNR/MnO₂/PNA NPs showed potential as excellent near-infrared (NIR)-excited nanoplatforms for photothermal therapy (PTT). Delightedly, the studies demonstrated that the GNR/MnO₂/PNA-DOX NPs showed a noticeable killing effect on tumor cells, whether it is tumor cell-triggered drug release or photothermal effect. Besides, it not only could enhance mitochondrial damage but also could inhibit the migration and invasion of tumor cells. Quite the reverse, it had little negative impact on normal cells. The feature can prevent anticancer drugs and nanoparticles from killing normal cells. Consequently, GNR/MnO₂/PNA NPs have potential applications in drug delivery and synergistic therapy due to these advantageous features.

Inorganic Nanomaterial for Biomedical Imaging of Brain Diseases

In the past few decades, brain diseases have taken a heavy toll on human health and social systems. Magnetic resonance imaging (MRI), photoacoustic imaging (PA), computed tomography (CT), and other imaging modes play important roles in disease prevention and treatment. However, the disadvantages of traditional imaging mode, such as long imaging time and large noise, limit the effective diagnosis of diseases, and reduce the precision treatment of diseases. The ever-growing applications of inorganic nanomaterials in biomedicine provide an exciting way to develop novel imaging systems. Moreover, these nanomaterials with special physicochemical characteristics can be modified by surface modification or combined with functional materials to improve targeting in different diseases of the brain to achieve accurate imaging of disease regions. This article reviews the potential applications of different types of inorganic nanomaterials in vivo imaging and in vitro detection of different brain disease models in recent years. In addition, the future trends, opportunities, and disadvantages of inorganic nanomaterials in the application of brain diseases are also discussed. Additionally, recommendations for improving the sensitivity and accuracy of inorganic nanomaterials in screening/diagnosis of brain diseases.

Tumor Diagnosis and Therapy Mediated by Metal Phosphorus-Based Nanomaterials

Metal phosphorus-based nanomaterials (Metal-P NMs) including metal phosphate nanomaterials, metal phosphide nanomaterials, and metal-black phosphorus (Metal-BP) nanocomposite are widely used in the field of biomedicine owing to their excellent physical and chemical properties, biocompatibility, and biodegradability. In recent years, metal phosphate nanomaterials and Metal-BP nanocomposite acted as medicine delivery system have made breakthroughs in tumor diagnosis including magnetic resonance imaging, fluorescence imaging, photoacoustic imaging, nuclear imaging, and therapies including chemotherapy, gene therapy, photothermal therapy, photodynamic therapy, and radiation therapy. Metal phosphate nanomaterials have good biodegradability, especially calcium-based metal phosphate nanomaterials can be dissolved into nontoxic ions and participate in the metabolisms of normal organs. Compared with metal phosphate nanomaterials, metal phosphide nanomaterials have excellent optical, magnetic, and catalytic properties, which can be used as multifunctional diagnostic nanoplatforms and therapeutic agents for chemodynamic therapy, photothermal therapy, or immunotherapy. The latest developments in Metal-P NMs, covering the range of preparation methods and biological applications, such as serving as drug carriers, tumor diagnosis, and therapy, are focused. All in all, the current trends, key issues, future prospects and challenges of Metal-P NMs are concluded and discussed, which are important for the development of this research field and shining more lights on this direction.

Plasmonic Oxygen Defects in MO3- x (M = W or Mo) Nanomaterials: Synthesis, Modifications, and Biomedical Applications

Nanomedicine is a promising technology with many advantages and provides exciting opportunities for cancer diagnosis and therapy. During recent years, the newly developed oxygen-deficiency transition metal oxides MO_{3- x} (M = W or Mo) have received significant attention due to the unique optical properties, such as strong localized surface plasmon resonance (LSPR) , tunable and broad near-IR absorption, high photothermal conversion efficiency, and large X-ray attenuation coefficient. This review presents an overview of recent advances in the development of MO_{3- x} nanomaterials for biomedical applications. First, the fundamentals of the LSPR effect are introduced. Then, the preparation and modification methods of MO_{3- x} nanomaterials are summarized. In addition, the biological effects of MO_{3- x} nanomaterials are highlighted and their applications in the biomedical field are outlined. This includes imaging modalities, cancer treatment, and antibacterial capability. Finally, the prospects and challenges of MO_{3- x} and MO_{3- x} -based nanomaterial for fundamental studies and clinical applications are also discussed.

Immunotherapy for Tumor Metastasis by Artificial Antigen-Presenting Cells via Targeted Microenvironment Regulation and T-Cell Activation

Effective expansion of T-cells without ex vivo stimulation and maintenance of their antitumor functions in the complex tumor microenvironment (TME) are still daunting challenges in T-cell-based immunotherapy. Here, we developed biomimetic artificial antigen-presenting cells (aAPCs), ultrathin MnO_x nanoparticles (NPs) functionalized with T-cell activators (anti-CD3/CD28 mAbs, CD), and tumor cell membranes (CMs) for enhanced lung metastasis immunotherapy. The aAPCs, termed CD-MnO_x@CM, not only efficiently enhanced the expansion and activation of intratumoral CD8⁺ cytotoxic T-cells and dendritic cells after homing to homotypic metastatic tumors but also regulated the TME to facilitate T-cell survival through catalyzing the decomposition of intratumoral H₂O₂ into O₂. Consequently, the aAPCs significantly inhibited the development of lung metastatic nodules and extended the survival of a B16-F10 melanoma metastasis model, while minimizing adverse events. Our work represents a new biomaterial strategy of inhibiting tumor metastasis through targeted TME regulation and in situ T-cell-based immunotherapy.

Manganese-Based Micro/Nanomotors: Synthesis, Motion, and Applications

As emerging micro/nano-scale devices, micro/nanomotors have been innovatively applied in the environmental and biomedical applications. In this paper, the recent advances of Mn-based micro/nanomotors (Mn-micro/nanomotors) in catalytic oxidation of organic contaminants and the mechanisms in decomposition of H₂ O₂ (e.g., the generation of O₂ bubbles and reactive oxygen species) are reviewed. The intrinsic characteristics and synthetic strategies of Mn-based materials are discussed, aiming to gain comprehensive understandings on the asymmetric design of micro/nanomotors. Mn-micro/nanomotors have many advantages such as flexible structures, biocompatibility, powerful motion, long lifetime, and low-cost as compared to noble-metal micro/nanomotors. These merits fulfil Mn-micro/nanomotors great promises from proof-of-concept studies to realistic applications, including pollutant decomposition, trace detection of heavy metal ions, oil removal, drug delivery, isolation of biological targets, and killing bacteria and cancer cells. The great flexibility in fabrication enables diverse and innovative strategies to address challenges for Mn-micro/nanomotors, including high consumption of H₂ O₂ and non-directional motion. Meanwhile, a perspective of Mn-micro/nanomotors in water remediation by coupling the motors with other Fenton/Fenton-like systems to enhance the catalytic activity and to yield more reactive oxygen species is presented. Directions to the design of on-demand H₂ O₂ -fueled Mn-micro/nanomotors for advanced purification of organic contaminants in aquatic systems are also proposed.

Regulating the synthesis rate and yield of bio-assembled FeS nanoparticles for efficient cancer therapy

Biosynthesis has gained growing interest due to its energy efficiency and environmentally benign nature. Recently, biogenic iron sulfide nanoparticles (FeS NPs) have exhibited excellent performance in environmental remediation and energy recovery applications. However, their biosynthesis regulation strategy and application prospects in the biomedical field remain to be explored. Herein, biogenic FeS NPs are controllably synthesized by Shewanella oneidensis MR-1 and applied for cancer therapy. Tuning the synthesis rate and yield of biogenic FeS NPs is realized by altering the initial iron precursor dosage. Notably, increasing the precursor concentration decreases and delays FeS NP biosynthesis. The biogenic FeS NPs (30 nm) are homogeneously anchored on the cell surface of S. oneidensis MR-1. Moreover, the good hydrophilic nature and outstanding Fenton properties of the as-prepared FeS NPs endow them with good cancer therapy performance. The intracellular location of the FeS NPs taken up is visualized with a soft X-ray microscope (SXM). Highly efficient cancer cell killing can be achieved at extremely low concentrations (<12 μg mL^-1), lower than those in reported works. Such good performance is attributed to the Fe²⁺ release, elevated ROS, reduced glutathione (GSH) consumption, and lipid hydroperoxide (LPO) generation. The resulting FeS NPs show excellent in vivo therapeutic performance. This work provides a facile, eco-friendly, and scalable approach to produce nanomedicine, demonstrating the potential of biogenic nanoparticles for use in cancer therapy.

pH-Regulating Nanoplatform for the "Double Channel Chase " of Tumor Cells by the Synergistic Cascade between Chlorine Treatment and Methionine-Depletion Starvation Therapy

During rapid proliferation and metabolism, tumor cells show a high dependence on methionine. The deficiency of methionine exhibits significant inhibition on tumor growth, which provides a potential therapeutic target in tumor therapy. Herein, ClO₂-loaded nanoparticles (fluvastatin sodium&metformin&bupivacaine&ClO₂@CaSiO₃@MnO₂-arginine-glycine-aspatic acid (RGD) (MFBC@CMR) NPs) were prepared for synergistic chlorine treatment and methionine-depletion starvation therapy. After outer layer MnO₂ was degraded in the high glutathione (GSH) tumor microenvironment (TME), MFBC@CMR NPs released metformin (Me) to target the mitochondria, thus interfering with the tricarboxylic acid (TCA) cycle and promoting the production of lactate. In addition, released fluvastatin sodium (Flu) by the NPs acted on monocarboxylic acid transporter 4 (MCT4) in the cell membrane to inhibit lactate leakage and induce a decrease of intracellular pH, further prompting the NPs to release chlorine dioxide (ClO₂), which then oxidized methionine, inhibited tumor growth, and produced large numbers of Cl^- in the cytoplasm. Cl^- could enter mitochondria through the voltage-dependent anion channel (VDAC) channel, which was opened by bupivacaine (Bup). The disruption of Cl^- homeostasis promotes mitochondrial damage and membrane potential decline, leading to the release of cytochrome C (Cyt-C) and apoptosis inducing factor (AIF) and further inducing cell apoptosis. To sum up, the pH-regulating and ClO₂-loaded MFBC@CMR nanoplatform can achieve cascade chlorine treatment and methionine-depletion starvation therapy toward tumor cells, which is of great significance for improving the clinical tumor treatment effect.

Biodegradable Nanocatalyst with Self-Supplying Fenton-like Ions and H2O2 for Catalytic Cascade-Amplified Tumor Therapy

Therapeutic nanosystems triggered by a specific tumor microenvironment (TME) offer excellent safety and selectivity in the treatment of cancer by in situ conversion of a less toxic substance into effective anticarcinogens. However, the inherent antioxidant systems, hypoxic environment, and insufficient hydrogen peroxide (H₂O₂) in tumor cells severely limit their efficacy. Herein, a new strategy has been developed by loading the chemotherapy prodrug disulfiram (DSF) and coating glucose oxidase (GOD) on the surface of Cu/ZIF-8 nanospheres and finally encapsulating manganese dioxide (MnO₂) nanoshells to achieve efficient DSF-based cancer chemotherapy and dual-enhanced chemodynamic therapy (CDT). In an acidic TME, the nanocatalyst can biodegrade rapidly and accelerate the release of internal active substances. The outer layer of MnO₂ depletes glutathione (GSH) to destroy the reactive oxygen defensive mechanisms and achieves continuous oxygen generation, thus enhancing the catalytic efficiency of GOD to burst H₂O₂. Benefiting from the chelation reaction between the released Cu²⁺ and DSF, a large amount of cytotoxic CuET products is generated, and the Cu⁺ are concurrently released, thereby achieving efficient chemotherapy and satisfactory CDT efficacy. Furthermore, the release of Mn²⁺ can initiate magnetic resonance imaging signals for the tracking of the nanocatalyst.

Recent progresses in the synthesis of MnO2 nanowire and its application in environmental catalysis

Nanostructured MnO₂ with various morphologies exhibits excellent performance in environmental catalysis owing to its large specific surface area, low density, and adjustable chemical properties. The one-dimensional MnO₂ nanowire has been proved to be the dominant morphology among various nanostructures, such as nanorods, nanofibers, nanoflowers, etc. The syntheses and applications of MnO₂-based nanowires also have become a research hotspot in environmental catalytic materials over the last two decades. With the continuous deepening of the research, the control of morphology and crystal facet exposure in the synthesis of MnO₂ nanowire materials have gradually matured, and the catalytic performance also has been greatly improved. Differences in the crystalline phase structure, preferably exposed crystal facets, and even the length of the MnO₂ nanowires will evidently affect the final catalytic performances. Besides, the modifications by doping or loading will also significantly affect their catalytic performances. This review carefully summarizes the synthesis strategies of MnO₂ nanowires developed in recent years as well as the influences of the phase structure, crystal facet, morphology, dopant, and loading amount on the catalytic performance. Besides, the cutting-edge applications of MnO₂ nanowires in the field of environmental catalysis, such as CO oxidation, the removal of VOCs, denitrification, etc., have been also summarized. The application of MnO₂ nanowire in environmental catalysis is still in the early exploratory stage. The gigantic gap between theoretical investigation and industrial application is still a great challenge. Compared with noble metal based traditional environmental catalytic materials, the lower cost of MnO₂ has injected new momentum and promising potential into this research field.

This review summarizes the synthesis strategies for MnO₂ nanowire and the influences of the phase structure, crystal facet, metal doping, and interface effect on its performance in various environmental catalysis processes.

Manganese-based advanced nanoparticles for biomedical applications: future opportunity and challenges

Nanotechnology is the most promising technology to evolve in the last decade. Recent research has shown that transition metal nanoparticles especially manganese (Mn)-based nanoparticles have great potential for various biomedical applications due to their unique fundamental properties. Therefore, globally, scientists are concentrating on the development of various new manganese-based nanoparticles (size and shape dependent) due to their indispensable utilities. Although numerous reports are available regarding the use of manganese nanoparticles, there is no comprehensive review highlighting the recent development of manganese-based nanomaterials and their potential applications in the area of biomedical sciences. The present review article provides an overall survey on the recent advancement of manganese nanomaterials in biomedical nanotechnology and other fields. Further, the future perspectives and challenges are also discussed to explore the wider application of manganese nanoparticles in the near future. Overall, this review presents a fundamental understanding and the role of manganese in various fields, which will attract a wider spectrum of the scientific community.

Safety Evaluation of Nanotechnology Products

Nanomaterials are now being used in a wide variety of biomedical applications. Medical and health-related issues, however, have raised major concerns, in view of the potential risks of these materials against tissue, cells, and/or organs and these are still poorly understood. These particles are able to interact with the body in countless ways, and they can cause unexpected and hazardous toxicities, especially at cellular levels. Therefore, undertaking in vitro and in vivo experiments is vital to establish their toxicity with natural tissues. In this review, we discuss the underlying mechanisms of nanotoxicity and provide an overview on in vitro characterizations and cytotoxicity assays, as well as in vivo studies that emphasize blood circulation and the in vivo fate of nanomaterials. Our focus is on understanding the role that the physicochemical properties of nanomaterials play in determining their toxicity.

Fenton Metal Nanomedicines for Imaging-guided Combinatorial Chemodynamic Therapy against Cancer

Chemodynamic therapy (CDT) is considered as a promising modality for selective cancer therapy, which is realized via Fenton reaction-mediated decomposition of endogenous H₂O₂ to produce toxic hydroxyl radical (•OH) for tumor ablation. While extensive efforts have been made to develop CDT-based therapeutics, their in vivo efficacy is usually unsatisfactory due to poor catalytic activity limited by tumor microenvironment, such as anti-oxidative systems, insufficient H₂O₂, and mild acidity. To mitigate these issues, we have witnessed a surge in the development of CDT-based combinatorial nanomedicines with complementary or synergistic mechanisms for enhanced tumor therapy. By virtue of their bio-imaging capabilities, Fenton metal nanomedicines (FMNs) are equipped with intrinsic properties of imaging-guided tumor therapies. In this critical review, we summarize recent progress of this field, focusing on FMNs for imaging-guided combinatorial tumor therapy. First, various Fenton metals with inherent catalytic performances and imaging properties, including Fe, Cu and Mn, were introduced to illustrate their possible applications for tumor theranostics. Then, CDT-based combinatorial systems were reviewed by incorporating many other treatment means, including chemotherapy, photodynamic therapy (PDT), sonodynamic therapy (SDT), photothermal therapy (PTT), starvation therapy and immunotherapy. Next, various imaging approaches based on Fenton metals were presented in detail. Finally, challenges are discussed, and future prospects are speculated in the field to pave way for future developments.

Multifunctional nanozyme for multimodal imaging-guided enhanced sonodynamic therapy by regulating the tumor microenvironment

Sonodynamic therapy (SDT) is a highly promising approach for cancer therapy, but its efficacy is severely hampered by the low specificity of sonosensitizers and the unfavorable characteristics of the tumor microenvironment (TME), such as hypoxia and glutathione (GSH) overexpression. To solve these problems, in this work, we encapsulated IR780 and MnO₂ in PLGA and linked Angiopep-2 (Ang) to synthesize a multifunctional nanozyme (Ang-IR780-MnO₂-PLGA, AIMP) to enhance SDT. With Ang functionalization to facilitate blood-brain barrier (BBB) penetration and glioma targeting, and through the function of IR780, these nanoparticles (NPs) showed improved targeting of cancer cells, especially mitochondria, and spread deep into tumor centers. Upon low-intensity focused ultrasound (LIFU) irradiation, reactive oxygen species (ROS) were produced and induced tumor cell apoptosis. Combined with the specific mitochondria-targeting ability of IR780, the sonodynamic effects were amplified because mitochondria are sensitive to ROS. In addition, MnO₂ exhibited enzyme-like activity, reacting with the high levels of hydrogen protons (H⁺), H₂O₂ and GSH in the TME to continuously produce oxygen and consume GSH, which further enhanced the effect of SDT. Moreover, Mn²⁺ can be released in response to TME stimulation and used as a magnetic resonance (MR) contrast agent. In addition, IR780 has photoacoustic (PA)/fluorescence (FL) imaging capabilities. Our results demonstrated that AIMP NPs subjected to LIFU triggering maximally enhanced the therapeutic effect of SDT by multiple mechanisms, including multiple targeting, deep penetration, oxygen supply in situ and GSH depletion, thereby significantly inhibiting tumor growth and distal metastasis without systemic toxicity. In summary, this multifunctional nanozyme provides a promising strategy for cancer diagnosis and treatment under the intelligent guidance of multimodal imaging (PA/FL/MR) and may be a safe clinical translational method.

A Honeycomb-Like Bismuth/Manganese Oxide Nanoparticle with Mutual Reinforcement of Internal and External Response for Triple-Negative Breast Cancer Targeted Therapy

Triple-negative breast cancer (TNBC) exhibits aggressive behavior and high levels of metastasis owing to its complex heterogeneous structure and lack of specific receptors. Here, tumor cell membrane (CM)-coated bismuth/manganese oxide nanoparticles (NPs) with high indocyanine green (ICG) payload up to 50.6 wt% (mBMNI NPs) for targeted TNBC therapy are constructed. The extra-high drug load Bi@Bi₂ O₃ @MnO_x NPs (honey-comb like structure) are formed by Kirkendall effect and electrostatic attraction. After modified with CM, they can home into tumor sites precisely, where they respond to internal overexpressed glutathione (GSH), releasing Mn²⁺ for chemodynamic therapy (CDT) with GSH depletion, while H₂ O₂ degrades into O₂ enabling relief of tumor hypoxia. In response to external near-infrared irradiation, mBMNI NPs intelligently generate vigorous heat and single oxygen (¹ O₂ ) for photothermal therapy (PTT) and photodynamic therapy (PDT) owing to high load. Importantly, O₂ production and GSH consumption during the internal response reinforce external PDT, while the heat generated through PTT during the external response promotes internal CDT. The honeycomb-like structure with high ICG load and mutual reinforcement between internal and external response results in excellent therapeutic effects against TNBC.

Construction of hollow polydopamine nanoparticle based drug sustainable release system and its application in bone regeneration

Nanomaterial-based drug sustainable release systems have been tentatively applied to bone regeneration. They, however, still face disadvantages of high toxicity, low biocompatibility, and low drug-load capacity. In view of the low toxicity and high biocompatibility of polymer nanomaterials and the excellent load capacity of hollow nanomaterials with high specific surface area, we evaluated the hollow polydopamine nanoparticles (HPDA NPs), in order to find an optimal system to effectively deliver the osteogenic drugs to improve treatment of bone defect. Data demonstrated that the HPDA NPs synthesized herein could efficiently load four types of osteogenic drugs and the drugs can effectively release from the HPDA NPs for a relatively longer time in vitro and in vivo with low toxicity and high biocompatibility. Results of qRT-PCR, ALP, and alizarin red S staining showed that drugs released from the HPDA NPs could promote osteogenic differentiation and proliferation of rat bone marrow mesenchymal stem cells (rBMSCs) in vitro. Image data from micro-CT and H&E staining showed that all four osteogenic drugs released from the HPDA NPs effectively promoted bone regeneration in the defect of tooth extraction fossa in vivo, especially tacrolimus. These results suggest that the HPDA NPs, the biodegradable hollow polymer nanoparticles with high drug load rate and sustainable release ability, have good prospect to treat the bone defect in future clinical practice.

Robust O2 Supplementation from a Trimetallic Nanozyme-Based Self-Sufficient Complementary System Synergistically Enhances the Starvation/Photothermal Therapy against Hypoxic Tumors

Much effort has been focused on novel nanomedicine for cancer therapy. However, tumor hypoxia limits the efficacy of various cancer therapeutics. Herein, we constructed a self-sufficient hybrid enzyme-based silk fibroin hydrogel system, consisting of Pt-decorated hollow Ag-Au trimetallic nanocages (HGN@Pt) and glucose oxidase (GOx), to supply O₂ continuously and consume glucose concurrently and, thereby, synergistically enhance the anti-cancer efficacy of a combined starvation and photothermal therapy operating in a hypoxic tumor microenvironment. Thanks to the cooperative effects of the active surface atoms (resulting from the island-like features of the Pt coating), the intrinsically hollow structure, and the strain effect induced by the trimetallic composition, HGN@Pt displayed efficient catalase-like activity. The enhancement in the generation of O₂ through the decomposition of H₂O₂ mediated by the as-designed nanozyme was greater than 400% when compared with that of hollow Ag-Pt bimetallic nanospheres or tiny Pt nanoparticles. Moreover, in the presence of HGN@Pt, significant amounts of O₂ could be generated within a few minutes, even in an acidic buffer solution (pH 5.8-6.5) containing a low concentration of H₂O₂ (100-500 μM). Because HGN@Pt exhibited a strong surface plasmon resonance peak in the near-infrared wavelength range, it could be used as a photothermal agent for hyperthermia therapy. Furthermore, GOx was released gradually from the SF hydrogel into the tumor microenvironment to mediate the depletion of glucose, leading to glucose starvation-induced cancer cell death. Finally, the O₂ supplied by HGN@Pt overcame the hypoxia of the microenvironment and, thereby, promoted the starvation therapeutic effect of the GOx-mediated glucose consumption. Meanwhile, the GOx-produced H₂O₂ from the oxidation of glucose could be used to regenerate O₂ and, thereby, construct a complementary circulatory system. Accordingly, this study presents a self-sufficient hybrid enzyme-based system that synergistically alleviates tumor hypoxia and induces an anti-cancer effect when combined with irradiation of light from a near-infrared laser.

Magnetic systems for cancer immunotherapy

Immunotherapy is a rapidly developing area of cancer treatment due to its higher specificity and potential for greater efficacy than traditional therapies. Immune cell modulation through the administration of drugs, proteins, and cells can enhance antitumoral responses through pathways that may be otherwise inhibited in the presence of immunosuppressive tumors. Magnetic systems offer several advantages for improving the performance of immunotherapies, including increased spatiotemporal control over transport, release, and dosing of immunomodulatory drugs within the body, resulting in reduced off-target effects and improved efficacy. Compared to alternative methods for stimulating drug release such as light and pH, magnetic systems enable several distinct methods for programming immune responses. First, we discuss how magnetic hyperthermia can stimulate immune cells and trigger thermoresponsive drug release. Second, we summarize how magnetically targeted delivery of drug carriers can increase the accumulation of drugs in target sites. Third, we review how biomaterials can undergo magnetically driven structural changes to enable remote release of encapsulated drugs. Fourth, we describe the use of magnetic particles for targeted interactions with cellular receptors for promoting antitumor activity. Finally, we discuss translational considerations of these systems, such as toxicity, clinical compatibility, and future opportunities for improving cancer treatment.

Recent progress in sono-photodynamic cancer therapy: From developed new sensitizers to nanotechnology-based efficacy-enhancing strategies

Many sensitizers have not only photodynamic effects, but also sonodynamic effects. Therefore, the combination of sonodynamic therapy (SDT) and photodynamic therapy (PDT) using sensitizers for sono-photodynamic therapy (SPDT) provides alternative opportunities for clinical cancer therapy. Although significant advances have been made in synthesizing new sensitizers for SPDT, few of them are successfully applied in clinical settings. The anti-tumor effects of the sensitizers are restricted by the lack of tumor-targeting specificity, incapability in deep intratumoral delivery, and the deteriorating tumor microenvironment. The application of nanotechnology-based drug delivery systems (NDDSs) can solve the above shortcomings, thereby improving the SPDT efficacy. This review summarizes various sensitizers as sono/photosensitizers that can be further used in SPDT, and describes different strategies for enhancing tumor treatment by NDDSs, such as overcoming biological barriers, improving tumor-targeted delivery and intratumoral delivery, providing stimuli-responsive controlled-release characteristics, stimulating anti-tumor immunity, increasing oxygen supply, employing different therapeutic modalities, and combining diagnosis and treatment. The challenges and prospects for further development of intelligent sensitizers and translational NDDSs for SPDT are also discussed.

Synthesis of Mesoporous CuO Hollow Sphere Nanozyme for Paper-Based Hydrogen Peroxide Sensor

Point-of-care monitoring of hydrogen peroxide is important due to its wide usage in biomedicine, the household and industry. Herein, a paper sensor is developed for sensitive, visual and selective detection of H2O2 using a mesoporous metal oxide hollow sphere as a nanozyme. The mesoporous CuO hollow sphere is synthesized by direct decomposition of copper-polyphenol colloidal spheres. The obtained mesoporous CuO hollow sphere shows a large specific surface area (58.77 m2/g), pore volume (0.56 cm3/g), accessible mesopores (5.8 nm), a hollow structure and a uniform diameter (~100 nm). Furthermore, they are proven to show excellent peroxidase-like activities with Km and Vmax values of 120 mM and 1.396 × 10-5 M·s-1, respectively. Such mesoporous CuO hollow spheres are then loaded on the low-cost and disposable filter paper test strip. The obtained paper sensor can be effectively used for detection of H2O2 in the range of 2.4-150 μM. This work provides a new kind of paper sensor fabricated from a mesoporous metal oxide hollow sphere nanozyme. These sensors could be potentially used in bioanalysis, food security and environmental protection.

Manganese oxide nanomaterials boost cancer immunotherapy

Immunotherapy, a strategy that leverages the host immune function to fight against cancer, plays an increasingly important role in clinical tumor therapy. In spite of the great success achieved in not only clinical treatment but also basic research, cancer immunotherapy still faces many huge challenges. Manganese oxide nanomaterials (MONs), as ideal tumor microenvironment (TME)-responsive biomaterials, are able to dramatically elicit anti-tumor immune responses in multiple ways, indicating great prospects for immunotherapy. In this review, on the basis of different mechanisms to boost immunotherapy, major highlighted topics are presented, covering adjusting an immunosuppressive TME by generating O2 (like O2-sensitized photodynamic therapy (PDT), programmed cell death ligand-1 (PD-L1) expression downregulation, reprogramming tumor-associated macrophages (TAMs), and restraining tumor angiogenesis and lactic acid exhaustion), inducing immunogenic cell death (ICD), photothermal therapy (PTT) induction, activating the stimulator of interferon gene (STING) pathway and immunoadjuvants for nanovaccines. We hope that this review will provide holistic understanding about MONs and their application in cancer immunotherapy, and thus pave the way to the translation from bench to bedside in the future.

Oxygen- and bubble-generating polymersomes for tumor-targeted and enhanced photothermal-photodynamic combination therapy

As a common feature of the tumor microenvironment (TME), hypoxia significantly impedes the effects of photodynamic therapy. Moreover, for tumor combination therapy, smart responsive and well-designed nanocarriers are highlighted to co-deliver different therapeutics, enhance drug delivery into target sites, and realize stimuli-responsive drug release. Herein, oxygen- and bubble-generating polymersomes (FIMPs) were developed for tumor-targeted and enhanced photothermal-photodynamic combination therapy. FIMPs efficiently co-encapsulated manganese dioxide (MnO₂) and the hydrophobic photosensitizer indocyanine green (ICG) within the hydrophobic membrane as well as the bubble-generating reagent NH₄HCO₃ in the internal cavity of the vesicles, and achieved pH/temperature/reduction multiple responsiveness. The CO₂ bubbles generated from the decomposition of NH₄HCO₃via laser irradiation or acidic environment and the cleavage of the copolymer disulfide bond in the reducing TME would destroy the vesicle structure for triggering drug release. In addition, oxygen can be produced to overcome tumor hypoxia through the high reaction activity of MnO₂ with endogenous H₂O₂. In vitro studies have shown that FIMPs achieved good photothermal conversion efficiency, promoted the generation of oxygen and reactive oxygen species (ROS), and thus effectively killed tumor cells. In vivo studies indicated that FIMPs effectively overcome the hypoxic microenvironment within tumors and significantly inhibit tumor growth with good biocompatibility. The rationally designed oxygen- and bubble-generating polymersomes have great potential to overcome the tumor hypoxia limitations for enhancing the photothermal-photodynamic combination therapeutic effect.

Harnessing Innate Immunity Using Biomaterials for Cancer Immunotherapy

The discovery of immune checkpoint blockade has revolutionized the field of immuno-oncology and established the foundation for developing various new therapies that can surpass conventional cancer treatments. Most recent immunotherapeutic strategies have focused on adaptive immune responses by targeting T cell-activating pathways, genetic engineering of T cells with chimeric antigen receptors, or bispecific antibodies. Despite the unprecedented clinical success, these T cell-based treatments have only benefited a small proportion of patients. Thus, the need for the next generation of cancer immunotherapy is driven by identifying novel therapeutic molecules or new immunoengineered cells. To maximize the therapeutic potency via innate immunogenicity, the convergence of innate immunity-based therapy and biomaterials is required to yield an efficient index in clinical trials. This review highlights how biomaterials can efficiently reprogram and recruit innate immune cells in tumors and ultimately initiate activation of T cell immunity against advanced cancers. Moreover, the design and specific biomaterials that improve innate immune cells' targeting ability to selectively activate immunogenicity with minimal adverse effects are discussed.

A biocompatible theranostic agent based on stable bismuth nanoparticles for X-ray computed tomography/magnetic resonance imaging-guided enhanced chemo/photothermal/chemodynamic therapy for tumours

Cancer is a leading cause of death worldwide and seriously threatens the health of humans. The current clinical treatments for cancer are not efficient and always lead to significant side effects. Herein, a biocompatible and powerful theranostic agent (Bi@mSiO₂@MnO₂/DOX) is fabricated using a facile stepwise reaction method. The Bi nanoparticles (NPs) are coated by mesoporous silica to protect the Bi NPs from oxidation, which guarantees the stable photothermal effect of the Bi NPs. When the Bi@mSiO₂@MnO₂/DOX nanocomposites (NCs) accumulate in the tumour site, hyperthermia is generated by Bi NPs under near-infrared (NIR) light irradiation for photothermal therapy (PTT), and the generated heat triggers the release of DOX for chemotherapy in the tumour. In addition, the MnO₂ of the NCs responsively catalyses endogenous H₂O₂ to generate O₂, raising the oxygen level to enhance the effect of chemotherapy in the tumour microenvironment (TME), and consumes glutathione (GSH) to produce Mn²⁺ for magnetic resonance (MR) imaging. Under acidic TME conditions, H₂O₂ and Mn²⁺ also produce toxic hydroxyl radical (·OH) for chemodynamic therapy (CDT). Furthermore, the Bi NPs can also be used as excellent contrast agents for X-ray computed tomography (CT) imaging of tumours with a high CT value (6.865 HU mM^-1). The Bi@mSiO₂@MnO₂/DOX NCs exhibit a powerful theranostic performance for CT/MR imaging-guided enhanced PTT/CDT/chemotherapy, which opens a new prospect to rationally design theranostic agents for tumour imaging.

Chemodynamic nanomaterials for cancer theranostics

It is of utmost urgency to achieve effective and safe anticancer treatment with the increasing mortality rate of cancer. Novel anticancer drugs and strategies need to be designed for enhanced therapeutic efficacy. Fenton- and Fenton-like reaction-based chemodynamic therapy (CDT) are new strategies to enhance anticancer efficacy due to their capacity to generate reactive oxygen species (ROS) and oxygen (O2). On the one hand, the generated ROS can damage the cancer cells directly. On the other hand, the generated O2 can relieve the hypoxic condition in the tumor microenvironment (TME) which hinders efficient photodynamic therapy, radiotherapy, etc. Therefore, CDT can be used together with many other therapeutic strategies for synergistically enhanced combination therapy. The antitumor applications of Fenton- and Fenton-like reaction-based nanomaterials will be discussed in this review, including: (iþ) producing abundant ROS in-situ to kill cancer cells directly, (ii) enhancing therapeutic efficiency indirectly by Fenton reaction-mediated combination therapy, (iii) diagnosis and monitoring of cancer therapy. These strategies exhibit the potential of CDT-based nanomaterials for efficient cancer therapy.

A brief review of non-invasive brain imaging technologies and the near-infrared optical bioimaging

Brain disorders seriously affect life quality. Therefore, non-invasive neuroimaging has received attention to monitoring and early diagnosing neural disorders to prevent their progress to a severe level. This short review briefly describes the current MRI and PET/CT techniques developed for non-invasive neuroimaging and the future direction of optical imaging techniques to achieve higher resolution and specificity using the second near-infrared (NIR-II) region of wavelength with organic molecules.

Aptamer-Targeted Photodynamic Platforms for Tumor Therapy

Achieving controlled and accurate delivery of photosensitizers (PSs) into tumor sites is a major challenge in conventional photodynamic therapy (PDT). Aptamer is a short oligonucleotide sequence (DNA or RNA) with a folded three-dimensional structure, which can selectively bind to specific small molecules, proteins, or the whole cells. Aptamers could act as ligands and be modified onto PSs or nanocarriers, enabling specific recognition and binding to tumor cells or their membrane proteins. The resultant aptamer-modified PSs or PSs-containing nanocarriers generate amounts of reactive oxygen species with light irradiation and obtain superior photodynamic therapeutic efficiency in tumors. Herein, we overview the recent progress in the designs and applications of aptamer-targeted photodynamic platforms for tumor therapy. First, we focus on the progress on the rational selection of aptamers and summarize the applications of aptamers which have been applied for targeted tumor diagnosis and therapy. Then, aptamer-targeted photodynamic therapies including various aptamer-PSs, aptamer-nanocarriers containing PSs, and aptamer-nano-photosensitizers are highlighted. The aptamer-targeted synergistically therapeutic platforms including PDT, photothermal therapy, and chemotherapy, as well as the imaging-guided theranostics, are also discussed. Finally, we offer an insight into the development trends and future perspectives of aptamer-targeted photodynamic platforms for tumor therapy.

Enhanced Peroxidase-mimicking Activity of Plasmonic Gold-modified Mn3 O4 Nanocomposites through Photoexcited Hot Electron Transfer

Enzyme-mimicking artificial nanomaterials often termed nanozymes have broad applications in many fields, including biosensing, pollutant degradation and cancer diagnosis. Herein, we introduce a plasmonic gold nanoparticle-modified Mn₃ O₄ nanozyme (Mn₃ O₄ -Au). Visible or near infrared light excitation into the plasmonic absorption band of the surface-bound gold nanoparticles enhances the catalytic oxidation of tetramethylbenzidine (TMB). The mechanism of light-enhanced peroxidase activity is proposed based on the Mn₃ O₄ conduction band mediated hot electron transfer from photoexcited gold nanoparticles to H₂ O₂ which undergoes further oxygen-oxygen bond cleavage to yield hydroxyl radical. The surface decoration of plasmonic gold nanoparticles endows Mn₃ O₄ -Au to be a light-regulated nanozyme.

A colorimetric sensing platform for azodicarbonamide detection in flour based on MnO2 nanosheets oxidative system

Azodicarbonamide (ADA), as a dough conditioner food additive in flour, can be turned into toxic biurea and semicarbazide after high temperature processing. Hence, the using of ADA in food material should be strictly controlled, and the detection of ADA is very important for consumers' safety and health. Herein, a simple and fast colorimetric strategy has been developed for ADA detection based on the MnO₂ nanosheets-3,3',5,5'-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO₂-TMB-GSH). Since the ADA can selectively react with GSH via oxidizing the sulfydryl (-SH) group of GSH to disulfide bond (S-S), which makes GSH unable to reduce MnO₂ nanosheets and restore its oxidase-like activity. The absorbance changes of the TMB solution depended on ADA content. The MnO₂-TMB-GSH colorimetric platform can detect the ADA with a linear range of 10 μmol L^-1 (11.6 ppm) to 400 μmol L^-1 (464 ppm), and the limit of detection (LOD) is 3.3 μmol L^-1 (3.51 ppm). Some potential interferences in real sample were tested and did not affect the MnO₂-TMB-GSH colorimetric platform for ADA detection. Furthermore, the sensing platform was applied for detecting ADA in real flour sample with a recovery of 96%-105% (RSD < 5%). This colorimetric method can effectively and rapidly detect ADA additives in flour less than the prescribed standard (45 mg kg^-1), which shows a great potential for visualization analysis and on-site detection of ADA in flour. A simple and fast colorimetric strategy has been developed for azodicarbonamide (ADA) detection based on the MnO₂ nanosheets-3,3',5,5'-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO₂-TMB-GSH).

Beyond Photo: Xdynamic Therapies in Fighting Cancer

Reactive oxygen species (ROS)-related therapeutic approaches are developed as a promising modality for cancer treatment because the aberrant increase of intracellular ROS level can cause cell death due to nonspecific oxidation damage to key cellular biomolecules. However, the most widely considered strategy, photodynamic therapy (PDT), suffers from critical limitations such as limited tissue-penetration depth, high oxygen dependence, and phototoxicity. Non-photo-induced ROS generation strategies, which are defined as Xdynamic therapies (X = sono, radio, microwave, chemo, thermo, and electro), show good potential to overcome the drawbacks of PDT. Herein, recent advances in the development of Xdynamic therapies, including the design of systems, the working mechanisms, and examples of cancer therapy application, are introduced. Furthermore, the approaches to enhance treatment efficiency of Xdynamic therapy are highlighted. Finally, the perspectives and challenges of these strategies are also discussed.

Doxorubicin-Loaded MnO2@Zeolitic Imidazolate Framework-8 Nanoparticles as a Chemophotothermal System for Lung Cancer Therapy

Doxorubicin-loaded MnO₂@zeolitic imidazolate framework-8 (DOX/MnO₂@ZIF-8) nanoparticles, a smart multifunctional therapeutic platform, were prepared for the treatment of lung cancer. The morphology, structure, and redox and photothermal properties of MnO₂@ZIF-8 were characterized by the corresponding methods. The anticancer drug DOX released from the DOX/MnO₂@ZIF-8 nanoparticles was measured. The cell viability of Lewis lung cancer (LLC) cells treated with MnO₂@ZIF-8 or DOX/MnO₂@ZIF-8 nanoparticles was determined using the cell counting kit-8 (CCK-8) method. The cellular uptake of DOX/MnO₂@ZIF-8 nanoparticles into LLC cells was observed using a confocal laser scanning microscope. TUNEL staining was performed to evaluate the in vivo therapeutic efficacy of DOX/MnO₂@ZIF-8 nanoparticles. The results showed that the as-prepared MnO₂@ZIF-8 nanoparticles had an average particle size of 155.59 ± 13.61 nm and the DOX loading efficiency was 12 wt %. MnO₂@ZIF-8 could react with H₂O₂ to generate O₂ and showed a great photothermal conversion effect both in vitro and in vivo. Up to 82% of total DOX could be released from DOX/MnO₂@ZIF-8 nanoparticles at pH = 5.0. The CCK-8 assay showed that MnO₂@ZIF-8 had low cytotoxicity to LLC cells, while DOX/MnO₂@ZIF-8 can significantly reduce the cell viability. DOX/MnO₂@ZIF-8 can be accumulated in LLC cells over time. Compared with PBS and DOX/MnO₂@ZIF-8 groups, the mice in the DOX/MnO₂@ZIF-8 + NIR group had the most apoptotic cells and significantly reduced tumor volume. In conclusion, these findings suggest that the as-prepared MnO₂@ZIF-8 nanoparticles with synergetic therapeutic effects by photothermal therapy and improved tumor microenvironment and as a pH-responsive nanocarrier for delivering the nonspecific anticancer drug DOX might be applied in the treatment of lung cancer.

Biocompatible BSA-MnO2 nanoparticles for in vivo timely permeability imaging of blood-brain barrier and prediction of hemorrhage transformation in acute ischemic stroke

Hemorrhage transformation (HT) is a frequent but maybe fatal complication following acute ischemic stroke due to severe damage of the blood-brain barrier (BBB). Quantitative BBB permeability imaging is a promising method to predict HT in stroke patients for a favorable prognosis. However, clinical gadolinium chelate-based magnetic resonance (MR) imaging of the stroke suffers from a relatively low sensitivity and potential side effects of nephrogenic systemic fibrosis and intracranial gadolinium deposition. Herein, BSA-MnO2 nanoparticles (BM NPs) fabricated by a facile disinfection-mimic method were employed for the permeability imaging of BBB in the stroke for the first time. The BM NPs showed a high T1 relaxivity (r1 = 5.9 mM-1 s-1), remarkable MR imaging ability, and good biocompatibility, allowing the noninvasive timely visualization of BBB permeability in the model rats of middle cerebral artery occlusion (MCAO). Furthermore, increased peak intensity, extended imaging duration, and expanded imaging region indicated by BM NPs in MR imaging showed a good prediction for the onset of HT in MCAO rats. Therefore, BM NPs hold an attractive potential to be an alternative biocompatible MR contrast agent for the noninvasive BBB permeability imaging in vivo, benefiting the fundamental research of diverse neurological disorders and the clinical treatment for stroke patients.

Improving the sensitivity of T 1 contrast-enhanced MRI and sensitive diagnosing tumors with ultralow doses of MnO octahedrons

Rationale: Sensitive and accurate imaging of cancer is essential for early diagnosis and appropriate treatment. For generally employed magnetic resonance imaging (MRI) in clinic, comprehending how to enhance the contrast effect of T₁ imaging is crucial for improving the sensitivity of cancer diagnosis. However, there is no study ever to reveal the clear mechanism of how to enhance the effect of T₁ imaging and accurate relationships of influencing factors. Herein, this study aims to figure out key factors that affect the sensitivity of T₁ contrast-enhanced MRI (CE-MRI), thereby to realize sensitive detection of tumors with low dose of CAs.

Methods: Manganese oxide (MnO) nanoparticles (NPs) with various sizes and shapes were prepared by thermal decomposition. Factors impacting T₁ CE-MRI were investigated from geometric volume, surface area, crystal face to r₂/r₁ ratio. T₁ CE-MR imaging of liver, hepatic and subcutaneous tumors were conducted with MnO NPs of different shapes.

Results: The surface area and occupancy rate of manganese ions have positive impacts on the sensitivity of T₁ CE-MRI, while volume and r₂/r₁ ratio have negative effects. MnO octahedrons have a high r₁ value of 20.07 mM^-1s^-1 and exhibit an excellent enhanced effect in liver T₁ imaging. ZDS coating facilitates tumor accumulation and cellular uptake, hepatic and subcutaneous tumors could be detected with MnO octahedrons at an ultralow dose of 0.4 mg [Mn]/kg, about 1/10 of clinical dose.

Conclusions: This work is the first quantitative study of key factors affecting the sensitivity of T₁ CE-MRI of MnO nanoparticles, which can serve as a guidance for rational design of high-performance positive MRI contrast agents. Moreover, these MnO octahedrons can detect hepatic and subcutaneous tumors with an ultralow dose, hold great potential for sensitive and accurate diagnosis of cancer with lower cost, less dosages and side effects in clinic.