Mn3O4 nanoparticles decorated porous reduced graphene oxide with excellent oxidase-like activity for fast colorimetric detection of ascorbic acid.

Mn3O4 nanoparticles composed of porous reduced graphene oxide nanosheets (Mn3O4@p-rGO) with enhanced oxidase-like activity were successfully fabricated through an in-situ approach for fast colorimetric detection of ascorbic acid (AA). The residual Mn2+ in the GO suspension of Hummers method was directly reused as the manganese source, improving the atom utilization efficiency. Benefiting from the uniform distribution of Mn3O4 nanoparticles on the surface of p-rGO nanosheets, the nanocomposite exhibited larger surface area, more active sites, and accelerated electron transfer efficiency, which enhanced the oxidase-like activity. Mn3O4@p-rGO nanocomposite efficiently activate dissolved O2 to generate singlet oxygen (1O2), leading to high oxidation capacity toward the substrate 3,3',5,5'-tetramethylbenzidine (TMB) without the extra addition of H2O2. Furthermore, the prominent absorption peak of the blue ox-TMB at 652 nm gradually decreased in the presence of AA, and a facile and fast colorimetric sensor was constructed with a good linear relationship (0.5-80 µM) and low LOD (0.278 µM) toward AA. Owing to the simplicity and excellent stability of the sensing platform, its practical application for AA detection in juices has shown good feasibility and reliability compared with HPLC and the 2, 4-dinitrophenylhydrazine colorimetric method. The oxidase-like Mn3O4@p-rGO provides a versatile platform for applications in food testing and disease diagnosis.

Green synthesis of Mn3O4 nanoparticles using Costus woodsonii flowers extract for effective removal of malachite green dye.

The pollution of organic dyes such as malachite green is one of the globally critical issues, calling for efficient mitigation methods. Herein, we developed green Mn3O4 nanoparticles synthesized using natural compounds extracted from Costus woodsonii flowers under an ultrasound-assisted mode. The materials were characterized using several physicochemical techniques such as Fourier-transform infrared spectroscopy, X-ray diffraction, Energy-dispersive X-ray spectroscopy, scanning electron microscopy, Raman spectroscopy, and N2 adsorption desorption isotherm measurement. The X-ray diffraction and N2 isotherm plots confirmed the presence of tetragonal γ-Mn3O4 phase and mesoporous structure, respectively. Carbonyl groups derived from flavonoids or carboxylic compounds were found in the surface of green Mn3O4 nanoparticles. The effect of pH, contact time, dose, and concentration on the adsorption of malachite green over green Mn3O4 was carried out. The maximum malachite green adsorption capacity for green Mn3O4 nanoparticles was 101-162 mg g-1. Moreover, kinetic and isotherm adsorption of malachite green obeyed Langmuir (Radj.2 = 0.980-0.995) and pseudo first-order models (Radj.2 = 0.996-1.00), respectively. Adsorption of malachite green over green Mn3O4 was a thermodynamically spontaneous process due to negative Gibbs free energy values (ΔGο < 0). Green Mn3O4 nanoparticles offered a high stability through the FR-IR spectra analysis. With a good recyclability of 4 cycles, green Mn3O4 nanoparticles can be used as potential adsorbent for removing malachite green dye from water.

Inflammation-sensing catalase-mimicking nanozymes alleviate acute kidney injury via reversing local oxidative stress.

BACKGROUND: The reactive oxygen species (ROS) and inflammation, a critical contributor to tissue damage, is well-known to be associated with various disease. The kidney is susceptible to hypoxia and vulnerable to ROS. Thus, the vicious cycle between oxidative stress and renal hypoxia critically contributes to the progression of chronic kidney disease and finally, end-stage renal disease. Thus, delivering therapeutic agents to the ROS-rich inflammation site and releasing the therapeutic agents is a feasible solution. RESULTS: We developed a longer-circulating, inflammation-sensing, ROS-scavenging versatile nanoplatform by stably loading catalase-mimicking 1-dodecanethiol stabilized Mn3O4 (dMn3O4) nanoparticles inside ROS-sensitive nanomicelles (PTC), resulting in an ROS-sensitive nanozyme (PTC-M). Hydrophobic dMn3O4 nanoparticles were loaded inside PTC micelles to prevent premature release during circulation and act as a therapeutic agent by ROS-responsive release of loaded dMn3O4 once it reached the inflammation site. CONCLUSIONS: The findings of our study demonstrated the successful attenuation of inflammation and apoptosis in the IRI mice kidneys, suggesting that PTC-M nanozyme could possess promising potential in AKI therapy. This study paves the way for high-performance ROS depletion in treating various inflammation-related diseases.

Neurotoxicity of Mn3O4 nanoparticles: Apoptosis and dopaminergic neurons damage pathway.

Mn3O4 nanoparticles (NPs) are used increasingly in various fields due to their excellent physiochemical properties. Previous studies have documented that Mn-based nanomaterials resulted in excess reactive oxygen species (ROS) generation and dopamine (DA) reduction both in vivo and in vitro experiments. However, little is known about the mechanism of ROS production and DA decrease induced by Mn-based nanomaterials. The present study was carried out to elucidate the mechanism of the co-incubation model of dopaminergic neuron PC12 cells and the synthesized Mn3O4 NPs. The results demonstrated that exposure to Mn3O4 NPs reduced cell viability, increased level of lactate dehydrogenase (LDH), triggered oxidative stress and induced apoptosis. Notably, the level of ROS was remarkably increased (>10-fold) with Mn3O4 NPs exposure. We also found that mitochondrial calcium Ca2+ uniporter (MCU) was up-regulated and the mitochondrial Ca2+ concentration ([Ca2+]mito) increased induced by Mn3O4 NPs in PC12 cells. Furthermore, the MCU inhibitor RuR significantly attenuated Mn3O4 NPs-induced [Ca2+]mito, ROS production and apoptosis. In PC12 cells, the decrease of DA content was mainly due to the downregulation of DOPA decarboxylase (DDC) expression caused by Mn3O4 NPs treatment. The expression of proteins related to DA storage system was not significantly affected by treatment.

Mn3O4 nanoparticles bearing 5-amino-2-mercapto benzimidazole moiety as antibacterial and antifungal agents.

The antibacterial and antifungal effects of non-functionalized and surface-functionalized Mn3O4 nanoparticles were comparatively analyzed to reason out the potential changes in antimicrobial activities due to functionalization with 5-amino-2-mercapto benzimidazole (AMB) molecule. The surface functionalization of Mn3O4 nanoparticles with AMB molecule was confirmed by the XRD result, which shows the shift in 2θ values with noticeable peaks. The surface morphology and functionalization of Mn3O4 nanoparticles were additionally confirmed by HR-SEM and EDAX studies. Antimicrobial activities were investigated by an agar-well-diffusion method using the bacteria Staphylococcus aureus and Pseudomonas aeruginosa and fungi Aspergillus niger. The functionalized Mn3O4 nanoparticles possess remarkable antibacterial and antifungal effect than the non-functionalized Mn3O4 nanoparticles and AMB molecule. The coating of low energy surface layer over metal oxide nanoparticles such as Mn3O4 offers an active surface toward both transfer of electron and the adsorption or desorption of water, inorganic ions, and other molecules, which leads to the increased antimicrobial activity of f-Mn3O4 nanoparticles.Communicated by Ramaswamy H. Sarma.

Enhanced Electrochemical Performances of Mn3O4/Heteroatom-Doped Reduced Graphene Oxide Aerogels as an Anode for Sodium-Ion Batteries.

Owing to their high theoretical capacity, transition-metal oxides have received a considerable amount of attention as potential anode materials in sodium-ion (Na-ion) batteries. Among them, Mn3O4 has gained interest due to the low cost of raw materials and the environmental compatibility. However, during the insertion/de-insertion process, Mn3O4 suffers from particle aggregation, poor conductivity, and low-rate capability, which, in turn, limits its practical application. To overcome these obstacles, we have successfully prepared Mn3O4 nanoparticles distributed on the nitrogen (N)-doped and nitrogen, sulphur (N,S)-doped reduced graphene oxide (rGO) aerogels, respectively. The highly crystalline Mn3O4 nanoparticles, with an average size of 15-20 nm, are homogeneously dispersed on both sides of the N-rGO and N,S-rGO aerogels. The results indicate that the N-rGO and N,S-rGO aerogels could provide an efficient ion transport channel for electrolyte ion stability in the Mn3O4 electrode. The Mn3O4/N- and Mn3O4/N,S-doped rGO aerogels exhibit outstanding electrochemical performances, with a reversible specific capacity of 374 and 281 mAh g-1, respectively, after 100 cycles, with Coulombic efficiency of almost 99%. The interconnected structure of heteroatom-doped rGO with Mn3O4 nanoparticles is believed to facilitate fast ion diffusion and electron transfer by lowering the energy barrier, which favours the complete utilisation of the active material and improvement of the structure's stability.

Prussian blue analogues derived electrocatalyst with multicatalytic centers for boosting oxygen reduction reaction in the wide pH range.

Due to the complex of oxygen reduction reaction (ORR), designing catalysts with multicatalytic centers is considered as a promising way for boosting the ORR. Herein, a multicatalytic centers electrocatalyst Fe3C/Mn3O4 encased by N-doped graphitic layers (FeMn PDA-900) is synthesized using iron manganese Prussian blue analogues and dopamine as the precursor. It exhibits a half-wave potential (E1/2) of 0.86 V for ORR and yields of H2O2 lower than 5% in 0.1 M KOH. Moreover, the prepared catalyst has also shown high catalytic ORR performance in both acidic and neutral electrolyte solutions, which exhibits the potential application in both the proton exchange membrane fuel cell and the microbial electrolysis cell. It is found that the good performance can be well explained by proton-coupled electron transfer mechanism due to the multicatalytic centers from Fe-Nx, Fe3C and Mn3O4 for providing enough active sites at the same time and the N-doped graphitic layers as a bridge for facilitating the electron transfer between the interfaces of Fe3C/Mn3O4 nanoparticles, which paves the way for protons and electrons transfer simultaneously and rapidly, and thus lowing the energy barrier and facilitating the ORR process. Therefore, FeMn PDA-900 is a promising candidate to replace precious metal-based ORR electrocatalysts at the whole pH range.

A drug delivery system based on nanocomposites constructed from metal-organic frameworks and Mn3O4 nanoparticles: Preparation and physicochemical characterization for BT-474 and MCF-7 cancer cells.

An integrated nanocomposite system comprising of manganese oxide (Mn3O4) nanoparticles, functioning as a tumor diagnostic agent, in conjunction with polyacrylic acid (PAA) and ZIF-8, as pH-sensitive drug delivery agents, and methotrexate (MTX), operating as a tumor biomarker and a therapeutic agent (dual mechanism of action), is applied for both diagnostic intentions and controlled delivery of the drug. Physicochemical characteristics of the constructed system, Mn3O4@PAA@ZIF-8/MTX, are investigated by several methods, including X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and electrochemical techniques. The in-vitro magnetic resonance imaging measurements was performed to show the efficiency of Mn3O4@PAA@ZIF-8 nanocomposite as a contrast agent where a relaxivity (r1) of 3.3 mM-1 s-1 is found. The loading ratio was found as 161 % which is four times larger than the value obtained for Mn3O4@PAA system in the same conditions, indicating high capability of the system for MTX delivery. The application of the nanocomposite as a dual pH-sensitive nanocarrier for MTX is studied through in-vitro drug release experiments at pHs of 5.4, 6.8 and 7.4. Interestingly, the results show that a large amount of loaded MTX drug (53 %) is released from the system during incubation and dialysis at pH 5.4, compared with that (20 % and 15 %), respectively, released at pHs 6.8 and 7.4 at the same conditions. The affinity of Mn3O4@PAA@ZIF-8/MTX nanocomposite for capturing of BT-474 and MCF-7 cancer cells was evaluated via impedance spectroscopy measurements. The results show that GC-Mn3O4@PAA@ZIF-8/MTX electrode captures the BT-474 and MCF-7 cancer cells, respectively, by factors of ∼2 and 196 compared with L929 normal cells. This affinity also shows the high selectivity of the system for MCF-7 cancer cells compared with BT-474.

Repeated administrations of Mn3O4 nanoparticles cause testis damage and fertility decrease through PPAR-signaling pathway.

Potential health hazards of nanomaterials on male reproductive system have received raising concerns. Even though Mn3O4 nanoparticles (Mn3O4-NPs) is highly effective in clinical diagnostic and therapeutic applications of human disease, its potential toxic effect on the male reproductive system has not been reported. In this study, the testis damage and fertility decrease of male rats were conducted to testify the experimental reproductive injury induced by Mn3O4-NPs. After repeated tail vein injection with 10 mg/kg/week Mn3O4-NPs for 0, 60 and 120 days, Mn3O4-NPs accumulated in the testes resulted in oxidative stress and disorder of normal serum sex hormones. Experiments in vivo and in vitro indicated that mitochondria-mediated cell apoptosis were triggered via oxidative stress, demonstrated by the upregulation of malondialdehyde (MDA) and the depolarization of mitochondrial membrane potential. Notably, Mn3O4-NPs significantly resulted in a reduction of the quantity/quality of sperm and finally caused astonishing fertility decrease. Our preliminary result implied that the application of Mn3O4-NPs could be a double-edged sword and careful consideration should be given to the clinical uses.

A Smart Nanotherapeutic Agent for in†vitro and in†vivo Reversal of Heavy-Metal-Induced Causality: Key Information from Optical Spectroscopy.

Human exposure to heavy metals can cause a variety of life-threatening disorders, affecting almost every organ of the body, including the nervous, circulatory, cardiac, excretory, and hepatic systems. The presence of heavy metal (cause) and induced oxidative stress (effect) are both responsible for the observed toxic effects. The conventional and effective way to combat heavy metal overload diseases is through use of metal chelators. However, they possess several side effects and most importantly they fail to manage the entire causality. In this study, we introduce citrate-functionalized Mn3 O4 nanoparticles (C-Mn3 O4 NPs) as an efficient chelating agent for treatment of heavy metal overload diseases. By means of UV/Vis absorbance and steady-state fluorescence spectroscopic techniques we investigated the efficacy of the NPs in chelation of a model heavy metal, lead (Pb). We also explored the retention of antioxidant properties of the Pb-chelated C-Mn3 O4 NPs using a UV/Vis-assisted DPPH assay. Through CD spectroscopic studies we established that the NPs can reverse the Pb-induced structural modifications of biological macromolecules. We also studied the in vivo efficacy of NPs in Pb-intoxicated C57BL/6j mice. The NPs were not only able to mobilize the Pb from various organs through chelation, but also saved the organs from oxidative damage. Thus, the C-Mn3 O4 NPs could be an effective nanotherapeutic agent for complete reversal of heavy-metal-induced toxicity through chelation of the heavy metal and healing of the associated oxidative stress.

In Situ Green Synthesis of the New Sandwichlike Nanostructure of Mn3O4/Graphene as Lubricant Additives.

Nanoparticles and two-dimensional (2D) nanosheets are well-investigated as lubricant additives, which can significantly reduce frictional energy consumption. However, the tribological properties of the additives will deteriorate because of the occurrence of aggregation in the lubricant and the difficulty in entering the frictional contact area. In the present work, the new sandwichlike nanostructure of Mn3O4 nanoparticles and graphene nanosheets (Mn3O4@G) has been developed by an in situ green synthesis method; i.e., the impurities of Mn2+ ions in crude graphite oxide as the precursor are directly transferred into Mn3O4 precipitate between the graphene sheets. The graphene has a lamellar structure without folds and wrinkles, and the Mn3O4 nanoparticles are not only uniformly anchored on the graphene surfaces but also intercalated in the layers of the graphene nanosheets. The Mn3O4@G exhibits excellent tribological properties and high stability because of a synergistic lubrication effect between the graphene nanosheets and the Mn3O4 nanoparticles. Even at an ultralow concentration (0.075 wt %) and a high temperature of 125 °C, the friction coefficient and the wear depth have been reduced by 75% and 97% compared with base oil, respectively. The synthesis method and the Mn3O4@G nanocomposite have significant potential in various tribological applications for saving energy.

Agar Hydrogel Template Synthesis of Mn3O4 Nanoparticles through an Ion Diffusion Method Controlled by Ion Exchange Membrane and Electrochemical Performance.

A novel strategy, ion diffusion method controlled by ion exchange membrane combining with agar hydrogel template, was reported for the synthesis of Mn3O4 nanoparticles without any oxidizing agents. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauere-Emmette-Teller (BET) isotherm were carried out to characterize the structure, morphology, pore size and distribution and specific surface area of the as-prepared nanomaterials. It is shown that the morphology and size of Mn3O4 nanoparticles can be controlled by the concentration of agar hydrogel. All the specific capacitances of the Mn3O4 samples prepared with agar hydrogel template are much higher than that of Mn3O4 prepared without any template agent. The Mn3O4 sample prepared at 1.5 g L-1 of agar hydrogel solution exhibits a highest specific capacitance of 183.0 F g-1 at the current density of 0.5 A g-1, which is increased by 293% compared with that of Mn3O4 synthesized without any template agent. The results indicate that the ion diffusion method controlled by ion exchange membrane combining with agar hydrogel template is a convenient and effective approach for preparing inorganic nanomaterials.

A theranostic system based on nanocomposites of manganese oxide nanoparticles and a pH sensitive polymer: Preparation, and physicochemical characterization.

A multifunctional nanocomposite theranostic system is constructed of manganese oxide (Mn3O4) nanoparticles (NPs), as a tumor diagnostic agent, in conjunction with polyacrylic acid (PAA), as a pH-sensitive drug delivery agent, and methotrexate (MTX), as a model of targeting agent and anticancer drug. Physicochemical characteristics of the Mn3O4@PAA/MTX system is studied in detail by several techniques, including X-ray and Auger photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and electrochemical methods. The system performance is studied based on (i) in-vitro MRI measurements to support efficiency of the Mn3O4@PAA NPs as a diagnostic agent, (ii) drug release performance of the Mn3O4@PAA/MTX NPs at pHs of 5.4 and 7.4 through in-vitro method to evaluate application of the NPs as pH-sensitive nanocarriers for MTX, and (iii) impedance spectroscopy measurements to show Mn3O4@PAA/MTX NPs affinity for capturing of cancer cells. The results show that (i) Mn3O4@PAA NPs can be used as a contrast agent in MRI measurements (r1 ≅ 6.5 mM-1 s-1), (ii) the MTX, loaded on Mn3O4@PAA NPs, is released faster and more efficient at pH 5.4 than 7.4, and (iii) the GC-Mn3O4@PAA/MTX electrode system captures the 4T1 cells 3.32 times larger than L929 cells.

Embedding MnO@Mn3 O4 Nanoparticles in an N-Doped-Carbon Framework Derived from Mn-Organic Clusters for Efficient Lithium Storage.

The first synthesis of MnO@Mn3 O4 nanoparticles embedded in an N-doped porous carbon framework (MnO@Mn3 O4 /NPCF) through pyrolysis of mixed-valent Mn8 clusters is reported. The unique features of MnO@Mn3 O4 /NPCF are derived from the distinct interfacial structure of the Mn8 clusters, implying a new methodological strategy for hybrids. The characteristics of MnO@Mn3 O4 are determined by conducting high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS) valence-state analyses. Due to the combined advantages of MnO@Mn3 O4 , the uniform distribution, and the NPCF, MnO@Mn3 O4 /NPCF displays unprecedented lithium-storage performance (1500 mA h g-1 at 0.2 A g-1 over 270 cycles). Quantitative analysis reveals that capacitance and diffusion mechanisms account for Li+ storage, wherein the former dominates. First-principles calculations highlight the strong affiliation of MnO@Mn3 O4 and the NPCF, which favor structural stability. Meanwhile, defects of the NPCF decrease the diffusion energy barrier, thus enhancing the Li+ pseudocapacitive process, reversible capacity, and long cycling performance. This work presents a new methodology to construct composites for energy storage and conversion.