MnO2 NPs Research Articles

Non-enzymatic colorimetric sensing of nitrite in fortified meat using functionalized drug mediated manganese dioxide

Nitrite and nitrate salts are important additives for processed meat products and their extreme uptake present acknowledged toxicity. Drug-mediated synthesis of manganese dioxide nanoparticles (MnO2 NPs) for the colorimetric detection of nitrite is being reported. Augmentin (Amoxicillin/clavulanic acid) drug was selected because of aromaticity and functionalities in its structure. Alongside the synthesis of MnO2 NPs, the sensing properties of the nanoparticles are enhanced through increased electron density from augmentin drug. Carboxylic acid having characteristic properties of conductivity (presence of carbonyl and hydroxyl group) was used as a coating material on the surface of MnO2 NPs to further increase the sensing properties. The characteristic peaks assigned to MnO2 NPs were confirmed through XRD, FTIR, and Raman spectroscopy. SEM image demonstrate round-shaped morphology and EDX observed a strong peak of the prepared MnO2 NPs. The maximum degradation of the prepared NPs was confirmed through TGA. The acetic acid capped MnO2 NPs were employed in nitrite sensing. Reaction conditions such as; (a) amount of capped MnO2 NPs (b) pH (c) time were optimized to get the best out of the proposed sensor. Colorimetric change from blackish to colorless occurs with a response time of only 8 min. The proposed sensor is capable to detect nitrite with a wide linear range of 1 × 10−8 - 3.6 × 10−6 M, a low detection limit of 1.04 × 10−7 M, and a limit of quantification 3.47 × 10−7 M with R2 of 0.999. The assembly of acetic acid-capped MnO2 NPs exhibits no reactivity towards Mg2+, Cu2+, K+, Ni2+, Pb2+, and Ca2+, etc, and is used to determine nitrite in Bacon chicken meat products.

Manganese dioxide nanoparticles green synthesis using lemon and curcumin extracts and evaluation of photocatalytic activity

Manganese dioxide nanoparticles (MnO2 NPs) were synthesized from aqueous manganese (II) acetate through the green route. Plant-based products such as lemon pulp and curcumin extracts were used as Mn2+ ion reducing and NPs stabilizing agents, respectively. UV–Visible spectrophotometer (UV–Vis) was used as a technique in measuring the relative yield of MnO2 NPs. The crystalline structure of synthesized MnO2 NPs was characterized using X-ray diffraction (XRD). Using Debye–Scherer equation, the average MnO2 NPs size was calculated as 41 nm. MnO2 NPs were also characterized using a scanning electron microscope (SEM) and FT-IR spectroscopy. MnO2 NPs photocatalytic activity was examined through methylene blue dye degradation under sunlight irradiation. Different variables such as exposure time, catalyst percentage, dye concentration, sunlight and dark conditions, and pH of the reaction medium were studied. MnO2 NPs were found to effectively degrade methylene blue dye about 95.3% in 7 h. Hence green synthesized MnO2 NPs could be used for water technology and industrial effluent treatment systems.

Anti-breast cancer potential of MnO2 nanoparticles using Terminalia chebula fruit extract against MCF-7 cell line through in vitro cell cycle and apoptotic studies

Since decades, cancer has become reason of major concern as it is the leading cause of mortality worldwide. Many therapeutic strategies have come up in the scientific world, but its pitiful to know that synthetic chemotherapeutic agents either cause adverse effects or cancer cells develop resistance to these agents. Plant derived chemotherapeutic agent present wide range of therapeutics, and most are yet to be discovered. In the present study, we have analysed the anti-proliferative, and apoptogenic properties of manganese oxide nanoparticles MnO2 NPs derived from Terminalia chebula (TC) fruit on breast adenocarcinoma, MCF7 cell lines. The formation of MnO2NPs was confirmed through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM). The morphology of the material was studied using SEM analysis, which suggested a agglomeration having spherical shape with an average diameter of 47.6 nm. Further, the TEM and HR-TEM images confirmed the rod shape of the as-prepared MnO2 NPs with an interplanar distance of 0.271 nm. The anticancer efficacy of MnO2NPs was evaluated against MCF-7 breast cancer cell line, which showed up to 86% inhibition of the cells at 320 μg/mL concentration.The MnO2 NPs was found to be cytotoxic, and was able to induce apoptosis in MCF7 cell lines.

Multiple fluorescence quenching effects mediated fluorescent sensing of captopril Based on amino Acids-Derivative carbon nanodots

Carbon nanodots (CNDs) were facilely synthesized through a pyrolysis procedure with histamine, an amino acid rich in element carbon and nitrogen, being the precursor. Taking advantage of the favorable fluorescence performance of CNDs, a multiple fluorescence quenching effects mediated fluorescent sensor was established for captopril (CAP) detection. MnO2 NPs were firstly combined with CNDs via electrostatic attraction and subsequently quenched the fluorescence. The quenching mechanisms were concluded to be the combined effects of fluorescence resonance energy transfer (FRET) and inner filtration effect (IFE). Subsequently CAP triggered a unique redox reaction and decomposed the quencher so that renewed the fluorescence. Hence, the sensitive and selective detection of CAP was achieved through the indication of fluorescence recovery efficiency. A proportional range of 0.4 ∼ 60 μmol L-1 with the LOD of 0.31 μmol L-1 was obtained. The sensor was further applied to the real sample detection and the satisfactory results revealed the practical value of CNDs. The facile synthesis of CNDs and brand-new sensing mechanism made it a novel fluorescent method and could improve the analysis of CAP.

Reversing Hypoxia with PLGA-Encapsulated Manganese Dioxide Nanoparticles Improves Natural Killer Cell Response to Tumor Spheroids.

The adoptive transfer of natural killer (NK) cells, which can recognize and obliterate cancer cells, provides a practical alternative to current treatment modalities to improve cancer patients' survival. However, translating NK cell therapies to treat solid tumors has proven challenging due to the tumor microenvironment (TME). Hypoxia in the TME induces immunosuppression that inhibits the cytotoxic function of NK cells. Thus, reversing hypoxia-induced immunosuppression is critical for effective adoptive NK cell immunotherapy. In this study, we use manganese dioxide nanoparticles (MnO2 NPs) to catalyze the degradation of tumor-produced hydrogen peroxide, thereby generating oxygen. For improved biocompatibility and modulation of oxygen production, the MnO2 NPs were encapsulated into poly(lactic-co-glycolic) to produce particles that are 116 nm in size and with a ζ-potential of +17 mV (PLGA-MnO2 NPs). The PLGA-MnO2 NPs showed first-order oxygen production and sustained high oxygen tension compared to equivalent amounts of bare MnO2 NPs in the presence of H2O2. The PLGA-MnO2 NPs were biocompatible, reduced hypoxia after penetration into the core of cancer spheroids, and decreased hypoxia-induced factor 1 α expression. Reducing hypoxia in the spheroid resulted in a decrease in the potent immunosuppressors, adenosine, and lactate, which was confirmed by electrospray ionization mass spectroscopy (ESI-MS). ESI-MS also showed a change in the metabolism of the amino acids aspartate, glutamine, and glutamate after hypoxia reduction in the cancer cells. Notably, the spheroids' microenvironment changes enhanced NK cells' cytotoxicity, which obliterated the spheroids. These results demonstrate that reducing hypoxia-induced immunosuppression in tumors is a potent strategy to increase the potency of cytotoxic immune cells in the TME. The developed NPs are promising new tools to improve adoptive NK cell therapy.

Cost-Effective, High-Yield Production of Biotemplated Catalytic Tubular Micromotors as Self-Propelled Microcleaners for Water Treatment.

Micro/nano-motors (MNMs) that combine attributes of miniaturization and self-propelled swimming mobility have been explored for efficient environmental remediation in the past decades. However, their progresses in practical applications are now subject to several critical issues including a complicated fabrication process, low production yield, and high material cost. Herein, we propose a biotemplated catalytic tubular micromotor consisting of a kapok fiber (KF, abundant in nature) matrix and manganese dioxide nanoparticles (MnO2 NPs) deposited on the outer and inner walls of the KF and demonstrate its applications for rapid removal of methylene blue (MB) in real-world wastewater. The fabrication is straightforward via dipping the KF into a potassium permanganate (KMnO4) solution, featured with high yield and low cost. The distribution and amount of MnO2 can be easily controlled by varying the dipping time. The obtained motors are actuated and propelled by oxygen (O2) bubbles generated from MnO2-triggered catalytic decomposition of hydrogen peroxide (H2O2), with the highest speed at 615 μm/s (i.e., 6 body length per second). To enhance decontamination efficacy and also enable magnetic navigation/recycling, magnetite nanoparticles (Fe3O4 NPs) are adsorbed onto such motors via an electrostatic effect. Both the Fe3O4-induced Fenton reaction and hydroxyl radicals from MnO2-catalyzed H2O2 decomposition can account for the MB removal (or degradation). Results of this study, taken together, provide a cost-effective approach to achieve high-yield production of the MNMs, suggesting an automatous microcleaner able to perform practical wastewater treatment.

A glutathione responsive nanoplatform made of reduced graphene oxide and MnO2 nanoparticles for photothermal and chemodynamic combined therapy

Based on the specific tumor microenvironment, characterized by an overproduction of H2O2 and a high glutathione (GSH) concentration, the cascade reactions of nanomaterials, capable of mediating GSH depletion and reactive oxygen species (ROS) generation, have become a popular strategy to increase cancer therapy efficiency. In this study, we exploited reduced graphene oxide (rGO), one of the most promising graphene-based materials, in combination with manganese dioxide nanoparticles (MnO2 NPs) to design a multifunctional nanoplatform (rGO@MnO2) for efficient photothermal/chemodynamic combined therapies. MnO2 NPs were anchored onto the surface of rGO nanosheets (rGO NSs). MnO2 NPs oxidize intracellular GSH, and the generated Mn2+ ions converted H2O2 into HO by Fenton reaction. Meanwhile, rGO NSs mediated photothermal therapy (PTT) could further kill cancer cells. High temperature caused by photothermal conversion increased Fenton reaction rate, which enhanced the efficiency of MnO2 NPs mediated chemodynamic therapy (CDT). Importantly, thanks to the enhanced cell uptake of MnO2 NPs favored by the delivery properties of rGO, rGO@MnO2 possessed higher lethality to cancer cells. The decrease in the nanomaterials’ effective dose would further improve biosecurity and reduce cost. Therefore, rGO@MnO2 have great potential in cancer therapy by exploiting the synergistic effect of PTT and photothermal/delivery effect enhanced CDT.

Bio-Active Free Direct Optical Sensing of Aflatoxin B1 and Ochratoxin A Using a Manganese Oxide Nano-System

Aflatoxins-B1 (AFB1) and Ochratoxin-A (OchA) are the two types of major mycotoxin produced by Aspergillus flavus, Aspergillus parasiticus fungi, Aspergillus carbonarius, Aspergillus niger, and Penicillium verrocusumv. These toxins are mainly found in metabolite cereals, corn, coffee beans, and other oil-containing food items. Excessive consumption of these toxins can be carcinogenic and lead to cancer. Thus, their rapid testing became essential for food quality control. Herein, manganese oxide nanoparticles (MnO2 nps) have been proposed to explore the interaction with AFB1 and OchA using UV-visible spectroscopy. MnO2 nps were synthesized using the co-precipitation method. They were pure and crystalline with an average crystallite size of 5–6 nm. In the UV-vis study, the maximum absorbance for MnO2 nps was observed around 260 nm. The maximum absorbance for AFB1 and OchA was observed at 365 and 380 nm, respectively, and its intensity enhanced with the addition of MnO2 nps. Sequential changes were observed with varying the concentration of AFB1 and OchA with a fixed concentration of MnO2 nps, resulting in proper interaction. The binding constant (kb) and Gibbs free energy for MnO2 nps-AFB1 and OchA were observed as 1.62 × 104 L g−1 and 2.67 × 104 L g−1, and −24.002 and −25.256 kJ/mol, respectively. The limit of detection for AFB1 and OchA was measured as 4.08 and 10.84 ng/ml, respectively. This bio‐active free direct sensing approach of AFB1 and OchA sensing can be promoted as a potential analytical tool to estimate food quality rapidly and affordable manner at the point of use.

Converting primary tumor towards an in situ STING-activating vaccine via a biomimetic nanoplatform against recurrent and metastatic tumors

Currently, vaccine is a promising tumor prevention modality in cancer therapy. However, it is hard to elicit robust antitumor immunity in patients already afflicted with tumor, inspiring a need for a firenew and subversive cancer therapeutic vaccine. Herein, we reported an in situ STING (stimulator of interferon genes)-activating vaccination (ISSAV) strategy to completely convert primary tumor towards an in situ therapeutic STING vaccine for initiating highly effective and personalized antitumor immune responses. This ISSAV strategy represented a broad-spectrum cancer therapeutic vaccine, which break the shackles of heterogeneity and immunosuppression. We developed an ideational ingenious biomimetic nanoplatform (CMM-DiR) for achieving ISSAV strategy, which encapsulated STING-agonist (MnO2 NPs) and immobilized photothermal agent (DiR). In the tumor microenvironment (TME), CMM-DiR realized burst release of Mn2+, increased the pH value of TME, alleviated tumor hypoxia and induced the expose of numerous tumor-associated antigens from cancer cells. Accordingly, the primary tumor had the dual-function of as adequate antigens and STING agonist depots, thus transforming into a therapeutic STING vaccine. Importantly, the robust antitumor immunity of nanoplatform was observed in primary tumor, recurrent tumor, metastatic tumor and multinodular tumor, demonstrating that this ISSAV represents a technological advancement in the field of cancer vaccinations and personalized immunotherapy.

Low-Cost Pressure Sensors Fabricated from Novel Polymeric Nanocomposites

Nanocomposites (NCs) can be used in several fields, for example, solar cells, biosensors, diodes, antibacterial, transistors…etc. In this paper,(poly (ethylene oxide)-polyvinylpyrrolidone-silicon oxide nanoparticles-manganese dioxide nanoparticles) NCs have been manufactured for pressure sensors with low weight, high sensitivity and lowcost. The nanocomposites were made up of various concentrations of poly (ethylene oxide) (PEO)-polyvinyl pyrrolidone (PVP)-silicon dioxide nanoparticles (SiO2 NPs) and manganese dioxide nanoparticles (MnO2 NPs). The electrical conductivity and dielectric properties of the nanocomposite are studied at room temperature. The dielectric properties of the NCs are examined in the frequency range (100 Hz–5 MHz). The AC electrical conductivity, dielectric constant, and dielectric losses increase with the weight percentages of MnO2 NPs. The dielectric constants and dielectric losses decrease when a frequency increases. The A. C electrical conductivity increases with the concentration of MnO2 NPs and the frequency. The nanocomposite was tested for the pressure sensors application in the pressure range (80–160) bar. The experimental results show that the electric capacitance of nanocomposites samplesis increased, as the pressure increases. Also, the electric capacitance of NCs increases with an increase in the weight percentages of MnO2 NPs. The NCs has a high sensitivity to pressure.

Fabrication of MnO2 NPs incorporated UiO-66 for the green and efficient oxidative desulfurization and denitrogenation of fuel oils

In this study, Manganese oxide nanoparticles (MnO2 NPs) are deposited over Zr-based UiO-66 molecular organic framework (MOF) resulting in MnO2/UiO-66 composite which is oxidized with NaClO for the catalytic oxidative desulfurization and denitrogenation of fuel oil. The as-synthesized composites were characterized via FE-SEM, EDX, BET, XPS and FT-IR techniques which confirmed the uniform deposition of MnO2 NPs and resulted in increased surface area and average mesoporous volume of pristine UiO-66. Catalytic results showed that MnO2/UiO-66 oxidized 2000 ppm of DBT (347 ppm Sulfur) and pyridine (502.8 ppm Nitrogen) in 3 min at O/S and O/N of 4, 0.06 g/15 mL catalyst dose and 25 °C. The mechanism behind the super-fast and highly efficacious performance of MnO2/UiO-66 is the ideal synergy among Mn4+, Zr4+ and NaClO species, which produced strong oxidizing •OH and •O2− radicals. Under the optimized reaction parameters, much higher removal of DBT and pyridine (100%) was achieved as compared to those of BT, 4,6-DMDBT, indole, and carbazole up to 6th cycles. This study provided important oxidant-catalyst system i.e. MnO2/UiO-66-NaClO for the highly efficacious, super-fast, and time and cost-effective alternative to the large scale oxidative desulfurization and denitrogenation of fuel oils.

Synthesis of Zinc Oxide, Titanium Dioxide and Magnesium Dioxide Nanoparticles and Their Prospective in Pharmaceutical and Biotechnological Applications

The use of nanoparticles for the therapeutic purpose is gaining pronounced importance. In the last two decades, a number of nanomedicines received regulatory approval and several showed promises through clinical trials. In this content, it is important to synthesize nanoparticles from various sources and to check its efficiency, especially its antibacterial activity. In today’s scenario number nanomedicines are proving useful to control multidrug resistance and since the mechanism of action of nanoparticles is totally different from the small molecules like antibiotics it obviates the chances of drug resistance. In this review, we discussed three metal-based nanoparticles prepared from various reducing sources namely Zinc Oxide Nanoparticle (ZnO NPs), Titanium Dioxide Nanoparticle (TiO2 NPs) and Magnesium Dioxide Nanoparticle (MnO2 NPs). The focus also made towards the safety assessment of the several nanoparticles. In addition, the exact interaction of the nanoparticles with the bacterial cell surface and the resultant changes also been highlighted. The review put forward the sources, method, and antibacterial success of these nanoparticles so that future nanomedicines could be put forward.

Diagnostic and therapeutic nanoenzymes for enhanced chemotherapy and photodynamic therapy.

Nanozymes, as a kind of artificial mimic enzymes, have superior catalytic capacity and stability. As lack of O2 in tumor cells can cause resistance to drugs, we designed drug delivery liposomes (MnO2-PTX/Ce6@lips) loaded with catalase-like nanozymes of manganese dioxide nanoparticles (MnO2 NPs), paclitaxel (PTX) and chlorin e6 (Ce6) to consume tumor's native H2O2 and produce O2. Based on the catalysis of MnO2 NPs, a large amount of oxygen was produced by MnO2-PTX/Ce6@lips to burst the liposomes and achieve a responsive release of the loaded drug (paclitaxel), and the released O2 relieved the chemoresistance of tumor cells and provided raw materials for photodynamic therapy. Subsequently, MnO2 NPs were decomposed into Mn2+ in an acidic tumor environment to be used as contrast agents for magnetic resonance imaging. The MnO2-PTX/Ce6@lips enhanced the efficacy of chemotherapy and photodynamic therapy (PDT) in bearing-tumor mice, even achieving complete cure. These results indicated the great potential of MnO2-PTX/Ce6@lips for the modulation of the TME and the enhancement of chemotherapy and PDT along with MRI tracing in the treatment of tumors.

Synthesis of ternary nanoparticles using the complexation-reduction method and their catalytic activities for hydrogen generation from formic acid

A complex-reduction method was used for the synthesis of glycine-capped copper nanoparticles (Gly-CuNPs). Glycine-Cu2+ was prepared at room temperature, and the resulting complex was treated with NaBH4. Gly-Cu/Ag and Gly-Cu/Ag/MnO2 were prepared by using the stepwise metal displacement plating method. Gly-Cu, Gly-Cu/Ag and Gly-Cu/Ag/MnO2 were employed as catalysts for hydrogen generation from the decomposition of formic acid. The alkaline barium hydroxide solution was employed to trap CO2 formation, and pseudo-first-order rate constants were calculated by using the kobs = 2.303/t log(Aα-A0/Aα-At) relation. Hydrogen generation followed fractional order kinetics with formic acid, and various kinetic parameters were calculated for various concentrations of promoter (sodium format), catalyst and temperature. The catalytic activity was found to increase with an increasing number of incorporated metals, and the order of reactivity was as follows: Gly-Cu/Ag/MnO2 > Gly-Cu/Ag > Gly-Cu. For Gly-Cu/Ag/MnO2, the values of activation parameters (Ea = 56 kJ/mol, ∆H# = 53 kJ/mol, ∆S# = − 68 J/K/mol) were determined with the Arrhenius and Eyring equations, which show higher catalytic efficiency than that of Gly-Cu/Ag (Ea = 69 kJ/mol, ∆H# = 66 kJ/mol, ∆S# = − 25 J/K/mol) due to the synergistic effect and strong interactions between the three metals. The catalytic stability and recyclability were excellent for five consecutive cycles, but the stability and recyclability decreased due to the higher reactivity of MnO2 NPs.

A novel method for synthesizing manganese dioxide nanoparticles using diethylenetriamine pentaacetic acid as a metal ion chelator

Manganese dioxide nanoparticles (MnO2 NPs) have been typically synthesized using polymers as reducing agents to reduce permanganate and/or as coating agents to increase colloidal stability. However, thus far, there have been no reports regarding methods for preparing MnO2 NPs using permanganate and only metal ion chelator. Herein, we proposed a new method for synthesizing MnO2 NPs by directly reducing permanganate using diethylenetriamine pentaacetic acid (DTPA) as a metal ion chelator. MnO2 NPs were synthesized by the simple reaction of DTPA as a chelating and reducing agent with different molar ratios of potassium permanganate (KMnO4). The synthetic DTPA/MnO2 produced nano-sized particles with sizes ranging from 208nm to 241nm, with negatively charged surfaces. The DTPA/MnO2 NPs that were synthesized at a molar ratio of 1:4 (DTPA:KMnO4) exhibited the highest stability and storage stability in deionized water. Further, the DTPA/MnO2 NPs could be rapidly degraded in the presence of hydrogen peroxide and simultaneously generate oxygen. Thus, in this study, we report the successful synthesis of novel MnO2 NPs using the metal ion chelator DTPA. Moreover, we believe that this NP-synthesis method will be widely applied to synthesize new types of MnO2 NPs using various metal chelators.

Manganese dioxide nanoparticles: synthesis, application and challenges

In recent days, manganese oxide nanoparticles (MnO2 NPs) have intrigued material science researches extensively due to its wide range of applications. They are widely used in energy storage devices (lithium-ion batteries, capacitors), catalysts, adsorbent, sensors and imaging, therapeutic activity, etc. Since they hold a lot of distinguished potentials, a robust protocol for cheap, stable, biocompatible and eco-friendly MnO2 NPs is necessary. They can be categorized into different phases like α, β, δ and others. Thus, owing to their peculiar character, they could be utilized for various purposes depending on the mode of action and applications. Hence, this review has summarized conventional methods, such as hydrothermal, sol–gel, oxidation–reduction used for the generation of MnO2 NPs. Likewise, morphological characterization by various spectroscopic techniques also outlined. It is found that the particular method of generation of MnO2 NPs is useful for a specific phase. Graphical representation of manganese dioxide nanoparticles: synthesis and application

Specific-oxygen-supply functionalized core-shell nanoparticles for smart mutual-promotion between photodynamic therapy and gambogic acid-induced chemotherapy

Photodynamic therapy (PDT) and chemotherapy of cancer both meet respective challenges. Tumor hypoxia, low penetration and high glutathione (GSH) level bear the brunt. Herein, a core-shell nanoparticle, with multi-function of hypoxia-responsiveness, specific oxygen supply and deep tumor penetration, was constructed for smart mutual-promotion between the both to overcome the respective restrictions. The nano platform (GC@MCS NPs) was composed of hypoxia-responsive hyaluronic acid-nitroimidazole (HA-NI) as shells, MnO2 NPs as oxygen modulators and reduction-responsive functionalized poly (l-glutamic acid) derivatives (γ-PFGA) as cores to deliver gambogic acid (GA) and Chlorine6 (Ce6). After endocytosis, the approximately 100 nm of GC@MCS NPs achieved hypoxia-responsive shell degradation and MnO2 release, followed by reduction-activated charge conversion to form positively charged cores. With the damage effect of superficial tumor cells by the partially released GA, GA&Ce6-loadedγ-PFGA penetrated deep inside through electronic interaction step by step. Upon irradiated with 638 nm of laser, widely permeated Ce6 was activated for enhanced PDT under the high oxygenation by MnO2 NPs. The generated reactive oxygen species (ROS) in return facilitated the GA-induced paraptosis by clearing high level of GSH. As a result, this mutual promotion strategy contributed to 92.41% of 4T1 tumor inhibition rate, exhibiting outstanding advantages. Our GC@MCS NPs provided a smart combination of chemo-photodynamic therapy and focused on addressing the tumor hypoxia and low penetration issues.

Physicochemical parameter influences and their optimization on the biosynthesis of MnO2 nanoparticles using Vernonia amygdalina leaf extract

The manganese dioxide nanoparticles (MnO2 NPs) were synthesized using Vernonia amygdalina leaf extract which was used as a reducing, capping, and stabilizing agents due to the presence of bioactive phytochemical compounds. Twenty five runs were designed to investigate the effect of V. amygdalina leaf extract ratio (A), initial potassium permanganate (KMnO4) concentration (B), pH (C), and reaction time (D) on the biosynthesized MnO2 NPs using 4-factor, 4-level D-Optimal Response Surface Quadratic Design Model approach. The relationship between physicochemical variables and absorption responses were established using transform second degree polynomial quadratic model. The effects of each absorption responses were analyzed by ANOVA principle using quadratic equations. A very low p-values (<0.0001), non-significant Lack of Fit F-values, and reasonable regression coefficient values (coefficient R2 = 0.9790, adjusted R2 = 0.9496, and predicted R2 = 0.8452) suggested that there is an effective correlation between experimental results and predicted values. Numerical and graphical optimized results demonstrated that the optimized conditions for the predicted absorbance at 320 nm (1.095) were suggested at 43.72%, 1.81 mM, 6.02, and 103.42 min for V. amygdalina leaf extract ratio, initial KMnO4 concentration, pH, and reaction time, respectively. Under these optimal conditions, the average absorbance from four experimental run was recorded to be 0.9678. This result was very closest to the predicted values. The average size elucidated by X-ray diffraction (XRD) analysis was found in the range between 20 nm and 22 nm. The stretching/or and vibrational, surface topography, thermal, and surface roughness as well as its porosity distributions were investigated by UV–Vis spectroscopy, Fourier transforms infrared (FTIR), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and Gwyddion software analysis.

Photosensitizer-Modified MnO2 Nanoparticles to Enhance Photodynamic Treatment of Abscesses and Boost Immune Protection for Treated Mice.

The emergence of drug-resistant bacteria and easy recurrence has been challenging in the clinical treatment of skin abscesses resulting from bacterial infections (e.g., by Staphylococcus aureus (S. aureus)). Herein, an antibacterial nanoagent capable of modulating the abscess microenvironment is designed to enhance photodynamic treatment of skin abscesses, and subsequently activate the immune system to effectively prevent abscess recurrence. In the system, manganese dioxide nanoparticles (MnO2 NPs) with high catalytic reactivity toward H2 O2 are modified with photosensitizer chlorine e6 (Ce6) and coated with polyethylene glycol (PEG). The obtained Ce6@MnO2 -PEG NPs, by triggering the decomposition of lesion endogenous H2 O2 , are able to effectively relieve the hypoxic abscess microenvironment during S. aureus infection. The light-triggered photodynamic bacterial killing effect could thus be remarkably enhanced, resulting in effective in vivo therapy of S. aureus-induced skin abscesses. Interestingly, a notable pathogen-specific immunological memory effect against future infection by the same species of bacteria is elicited after such treatment, owing to the release of bacterial antigens post photodynamic therapy (PDT) together with the adjuvant-like function of manganese ions to activate the host immune system. This work thus presents a new type of photodynamic nanoagent particularly promising for highly effective light-triggered abscess treatment and prevention of abscess recurrence.

MnO2 coated with graphene by galvanostatic electrodeposition and its enhanced electrocatalysis for oxygen reduction

Manganese oxides (MnOx) are expected to be highly active catalysts for O2 electroreduction. However, MnOx are prone to aggregation, thus reducing their catalytic active sites. Herein, a composite of spherical MnO2 coated with reduced graphene oxide (denoted as MnO2@RGO) was fabricated by a facile and green step galvanostatic electrodeposition. The obtained MnO2@RGO is composed of a RGO lamina shell (10 nm) and spherical MnO2 core (100 nm), which were confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunner–Emmet–Teller (BET) measurement, Raman, and X-ray photoelectron spectroscopy (XPS). The obtained composite exhibited a high specific surface area of 251.3 m2 g−1. The as-prepared MnO2@RGO composite displayed a more positive onset potential of 0.86 V vs. reversible hydrogen electrode (RHE), higher kinetic current density (11.23 mA cm−2 at 0.2 V), and higher electron transfer number in OH− solution (n ≈ 3.94) for oxygen reduction reaction (ORR) compared to MnO2 NPs scattered on the surface of RGO (MnO2/RGO), bulk MnO2 NPs, and RGO. The enhanced activity was further demonstrated by the lower Tafel slope (72 mV dec−1). Moreover, MnO2@RGO exhibited greater “tolerance to methanol,” “anti-CO poisoning” ability, and catalytic stability compared to commercial Pt/C catalyst. The results indicated that the prepared MnO2@RGO composite can be a potential low-cost and effective electrocatalyst for ORR. MnO2 coated with reduced graphene oxide has been firstly prepared by step galvanostatic process and shows enhanced catalytic activity and stability for oxygen reduction reaction.