MnO2 Nanosheets Research Articles

Nickel nanoparticles modified MnO nanosheet arrays for high-performance supercapacitor with long-lasting and sustainable capacitance increase

Rational design of binder-free electrode materials with good electronic conductivity, high specific capacitance and long cyclic stability is of great interest for high-performance pseudocapacitors. Herein, an etching-induced co-precipitation approach coupled with reduction and dehydration is developed, through which the Ni-modified MnO (Ni/MnO) nanosheet arrays can be successfully grown on Ni foam and directly used as binder-free electrode for pseudocapacitors. During the synthesis, the nickel foam acts as not only conductive substrate but also nickel source for the growth of the composite nanosheet arrays. With the introduction of Ni nanoparticles, the conduction of the electrons is efficiently promoted. Meanwhile, the porous structure of the Ni/MnO nanosheet arrays gives rise to the larger contact area between the active material and the electrolyte. Furthermore, the Ni nanoparticles on the MnO nanosheets and the Ni substrate can both participate in the electrochemical charge storage processes, which exerts extra positive effects on the improvement of the capacitance for the composite material. As a result, the as-prepared Ni/MnO nanosheet arrays electrode demonstrates excellent electrochemical performances with high specific capacitance achieved. More strikingly, a long-lasting and sustainable capacitance increase upon cycling is observed, which is systematically investigated and discussed. Overall, this work provides a facile and effective method to fabricate composite pseudocapacitive material with a hierarchical structure, which may open a promising direction for high-performance pseudocapacitors.

A redox-coupled carbon dots-MnO2 nanosheets based sensory platform for label-free and sensitive detection of E. coli

Abstract An enzymatic redox reaction was exploited in developing a novel carbon dots (CDs)-manganese dioxide (MnO2) nanosheets based fluorescent sensing platform for sensitive, selective, and rapid detection of Escherichia coli (E. coli) in aqueous media. The detection of E. coli is achieved by rationally placing a relay of redox reactions mediated by enzyme and a redox couple of p-benzoquinone (BQ) and hydroquinone (HQ). Initially, CDs-MnO2 forms a FRET conjugate and the inherent fluorescence of CDs remains in the turn-off state. Presumably, the enzymes present in E. coli respiratory pathway (such as NADH-quinone reductase), converts BQ to HQ by two-electron reduction, which in turn reacts with MnO2 nanosheets to reduce it to free Mn2+ ions. As MnO2 nanosheets disintegrate, the CDs are released from electrostatic interaction and go to a disperse phase in the aqueous solution to emit blue fluorescence. Thus, it devises a label-free sensing assay for the detection of live E. coli. The LOD was determined as 50 CFU/mL for E. coli. The utility of this cost-effective sensing tool was demonstrated in real-sample analysis and quantitation of E. coli was done in rainwater and food samples. Further, the fluorescent images of bacterial solutions and agar-polymer based test-strips were captured on a smartphone and analyzed using ImageJ for a practical demonstration of on-site detection of E. coli. The present method with merits like cost-effective synthesis from biomass, rapid detection, low detection limit, high selectivity offers a viable alternative to existing detection tools for on-site detection and quantitation of E. coli.

Atomically Dispersed Y or La on Birnessite-Type MnO2 for the Catalytic Decomposition of Low-Concentration Toluene at Room Temperature.

Room-temperature catalytic decomposition of low-concentration volatile organic compounds (VOCs) in indoor air is an exciting dream to solve their pollution. Herein, two kinds of rare-earth elements (Y and La) were separately doped into birnessite-type MnO2 nanosheets in the form of single atoms by the hydrothermal method. As-synthesized La/MnO2 achieved 100% removal of 10 ppm toluene at 40 °C under the gas hourly space velocity of 60 L g-1 h-1, which was even somewhat better than the single Pt atom-doped MnO2. In addition, La/MnO2 showed the good durability at room temperature for 0.5 ppm toluene removal under the GHSV of 300 L g-1 h-1 and could be effectively regenerated at 105 °C. GC/FID, online-MS and TD-GC/MS analysis demonstrated that only ignorable trace benzene (∼3.4 ppb, < one thousandth of inlet toluene) was generated in the gas phase during catalytic decomposition of 10 ppm toluene at room temperature. This research sheds light on the development of low cost and high activity catalysts for low-concentration VOC oxidation at room temperature.

Thick Electrodes: Alternative‐Ultrathin Assembling of Exfoliated Manganese Dioxide and Nitrogen‐Doped Carbon Layers for High‐Mass‐Loading Supercapacitors with Outstanding Capacitance and Impressive Rate Capability (Adv. Funct. Mater. 17/2021)

In article number 2009632, Bong Gill Choi and co-workers report alternative-ultrathin assembling MnO2 and nitrogen-doped carbon nanosheets to achieve high-performance supercapacitors. The heterostuctured and interlayer-expanded structure of the MnO2/carbon enables fast and efficient electron ion transfer in a thick electrode. The resulting MnO2/carbon electrode shows outstanding electrochemical performance at an ultrahigh mass loading of 19.7 mg cm−2, ultrahigh capacitance, rate capability, and energy density.

Sensitive detection of butyrylcholinesterase activity based on a separation-free photothermal assay

Butyrylcholinesterase (BChE), a regulator for the cholinesterase activity in serum, is an important index for clinical diagnosis of organophosphorus poisoning and liver related disease. However, the assays for BChE activity are highly dependent on expensive and bulk equipment and professional operators, which limits its straightforward and portable detection. In this work, we proposed a straightforward and sensitive photothermal assay for the detection of BChE activity, avoiding the use of expensive instrument, professional operators, and separation process. Polydopamine (PDA) nanoparticles can be produced through the oxidation of dopamine by MnO2 nanosheets, which show a rather strong photothermal features. Hydrolyzation of substrate into thiocholine and butyrate happens after introducing BChE. The generated thiocholine and butyrate inhibit the formation of PDA nanoparticle through reducing MnO2 into Mn2+ and creating an acidic environment, respectively. Those effects lead to the decreasing of photothermal efficiency of the reaction system, resulting in the decreasing on temperature change. Quantitative detection of BChE activity is achieved by recording the temperature change of system, using a common device, with a limit of detection of 40.65 U/L calculated. The presented results provide a clue for developing straightforward and portable photothermal assay for BChE, which shows great potential for their clinical applications.

Two-Photon CQDs-Based Dual-Mode Nanoprobe for Fluorescence Imaging and Magnetic Resonance Imaging of Intracellular Wide pH.

Biological fluorescence imaging technologies have attracted a lot of attention and have been widely used in biomedical fields. Compared with other technologies, fluorescence imaging has a lower cost, higher sensitivity, and easier operation. However, due to the disadvantages of one-photon (OP) fluorescence imaging, such as low spatial and poor temporal resolution and poor tissue permeability depth, the application of OP fluorescence imaging has some limitations. Though two-photon (TP) fluorescence imaging can well overcome these shortcomings of OP, the single-mode imaging remains deficient. Therefore, dual-mode imaging combined with TP imaging and magnetic resonance imaging (MRI) can make up for the deficiency well, which make dual-mode imaging for the early diagnosis of diseases more accurate. Hence, a dual-mode nanoprobe TP-CQDs@MnO2 was designed for probing the fluorescence/MR dual-mode imaging strategy of intracellular H+ by using TP-CQDs (two photon-carbon quantum dots) and MnO2 nanosheets. The MnO2 nanosheets treated as fluorescence quenching agents of TP-CQDs exhibited a supersensitive response to H+, which made the fluorescence signals turn "off" to "on" for TP fluorescence imaging, in the meantime, large amounts of Mn2+ were generated for MRI. A dual-mode nanoprobe TP-CQDs@MnO2 can monitor intracellular wide pH (4.0-8.0), and the fluorescence intensity of TP-CQDs@MnO2 has recovered up to more than six times and the corresponding results of MRI were satisfactory. TP fluorescence imaging of cells and tissues showed higher detection sensitivity and deeper tissue penetration (240.0 μm) than OP. The dual-mode imaging platform hold great promise for pH-related early diagnosis and treatment, which has great potential to improve clinical efficacy.

Oxidase-like Nanozyme-Mediated Altering of the Aspect Ratio of Gold Nanorods for Breaking through H2O2-Supported Multicolor Colorimetric Assay: Application in the Detection of Acetylcholinesterase Activity and Its Inhibitors

A convenient, fast, and colorful colorimetric platform with high resolution for acetylcholinesterase (AChE) activity and its inhibitors detection based on the regulation of oxidase-like nanozyme-mediated etching of gold nanorods (AuNRs) has been proposed in this work. MnO2 nanosheets are selected as the nanozyme. Their excellent oxidase-like activity enables the etching process to proceed smoothly without the usage of unstable H2O2. When AChE is present, it catalytically hydrolyzes acetylthiocholine (ATCh) to thiocholine (TCh). With high reducing ability, TCh induces the decomposition of MnO2 nanosheets, causing them to lose their oxidase-like activity. Thus, the etching of AuNRs is hampered. Consequently, with the increasing concentration of AChE, an apparent change in the AuNRs solution color is observed. The proposed platform achieves high-sensitivity detection of AChE (limit of detection = 0.18 mU/mL). Furthermore, the proposed platform also has been demonstrated its applicability for its inhibitors detection. Benefiting from the advantages of convenient and high resolution of visual readout, the proposed platform holds great potential for the detection of AChE and its inhibitors in clinical diagnosis.

Highly sensitive and selective detection and intracellular imaging of glutathione using MnO2 nanosheets assisted enhanced fluorescence of gold nanoclusters

Glutathione (GSH) plays a critical role in biological defense system and is associated with numerous human pathologies. However, it still remains a challenge for fluorescent detection of GSH over cysteine (Cys) and homocysteine (Hcy) because of their similar structures. In this work, MnO2 nanosheets can efficiently quench the fluorescence of gold nanoclusters (Met-AuNCs) prepared by blending methionine and HAuCl4 owing to their superior absorption capability. However, GSH can reduce MnO2 nanosheets into Mn2+ which leads to the fluorescence recovery of Met-AuNCs. More intriguingly, GSH can dramatically and selectively enhance the fluorescence intensity of Met-AuNCs. Hence, a low background, ultrasensitive fluorescent detection of GSH was obtained with a detection limit of 68 nM. Moreover, the assay has been successfully used for GSH detection in human serum samples and cellular imaging with high selectivity over Cys and Hcy.

Enhanced catalytic ozonation of ibuprofen using a 3D structured catalyst with MnO2 nanosheets on carbon microfibers

Heterogeneous catalytic ozonation is an effective approach to degrade refractory organic pollutants in water. However, ozonation catalysts with combined merits of high activity, good reusability and low cost for practical industrial applications are still rare. This study aims to develop an efficient, stable and economic ozonation catalyst for the degradation of Ibuprofen, a pharmaceutical compound frequently detected as a refractory pollutant in treated wastewaters. The novel three-dimensional network-structured catalyst, comprising of δ-MnO2 nanosheets grown on woven carbon microfibers (MnO2 nanosheets/carbon microfiber), was synthesized via a facile hydrothermal approach. Catalytic ozonation performance of Ibuprofen removal in water using the new catalyst proves a significant enhancement, where Ibuprofen removal efficiency of close to 90% was achieved with a catalyst loading of 1% (w/v). In contrast, conventional ozonation was only able to achieve 65% removal efficiency under the same operating condition. The enhanced performance with the new catalyst could be attributed to its significantly increased available surface active sites and improved mass transfer of reaction media, as a result of the special surface and structure properties of this new three-dimensional network-structured catalyst. Moreover, the new catalyst displays excellent stability and reusability for ibuprofen degradation over successive reaction cycles. The facile synthesis method and low-cost materials render the new catalyst high potential for industrial scaling up. With the combined advantages of high efficiency, high stability, and low cost, this study sheds new light for industrial applications of ozonation catalysts.

Preparation of carbonized sponge/MnO2 composite for energy storage application

The simple and low-cost supercapacitor preparation strategy has received great attention at present. In our work, the MnO2 nanosheets were equably grown on carbon foam by electrodeposition to synthesize electrode. The carbon foam (CF) is a three-dimensional (3D) conductive skeleton that guarantees the rapid transfer of ions and electrons. An appropriate amount of MnO2 nanosheets provide excellent pseudocapacitance properties. The composite material reaches the highest specific capacitance of 365 F g−1 at 1 A g−1 and the cycling test shows capacitance retention of 87.7% over 5000 cycles at a current density of 10 A g−1 in a three-electrode system. Meanwhile, the device revealed a maximum energy density of 22.2 Wh kg−1 at a power density of 1000 W kg−1. Two assembled supercapacitors were enough to light up a timer and the material has a certain practical value.

Tumor Microenvironment-Activatable Cyclic Cascade Reaction to Reinforce Multimodal Combination Therapy by Destroying the Extracellular Matrix.

The optimal therapy effect of tumors is frequently restricted by the dense extracellular matrix (ECM) and anoxia. Herein, an intelligent BPNs-Arg-GOx@MnO2 (BAGM) nanozyme is innovatively designed as a multimodal synergistic therapeutic paradigm that possesses both nitric oxide (NO) self-supplying and ECM degradation properties to reinforce the therapy effect by a tumor microenvironment (TME)-activatable cyclic cascade catalytic reaction. This theranostic nanoplatform is constructed by using polyethyleneimine-modified black phosphorus nanosheets as a "fishnet" to attach l-Arginine (l-Arg) and glucose oxidase (GOx) and then depositing mini-sized MnO2 nanosheets (MNs) on the surface by a facile situ biomineralization method. As an intelligent "switch", the MNs can effectively trigger the cascade reaction by disintegrating intracellular H2O2 to release O2. Then, the conjugated GOx can utilize O2 production to catalyze intracellular glucose to generate H2O2, which not only starves the tumor cells but also promotes oxidation of l-Arg to NO. Thereafter, matrix metalloproteinases will be activated by NO production to degrade the dense ECM and transform matrix collagen into a loose state. In turn, a loose ECM can enhance the accumulation of the BAGM nanozyme and thereby reinforce synergistic photothermal therapy/starvation therapy/NO gas therapy. Both in vitro and in vivo results indicate that the TME-tunable BAGM therapeutic nanoplatform with cascade anticancer property and satisfactory biosecurity shows potential in nanomedicine.

Methylene blue intercalated layered MnO2 nanosheets for high-sensitive non-enzymatic ascorbic acid sensor

Methylene blue intercalated layered MnO2 nanosheets for high-sensitive non-enzymatic ascorbic acid sensor

MOF-derived Fe2O3 decorated with MnO2 nanosheet arrays as anode for high energy density hybrid supercapacitor

The strategy of complementing the optimal energy storage potential range is used to construct core–shell M−Fe 2 O 3 @MnO 2 as an advanced anode material. The M−Fe 2 O 3 @MnO 2 //NiCo 2 O 4 HSC delivers a high energy density of 86.8 Wh kg −1 , and two such devices can light 25 LEDs for more than 210 min. • Strategies for complementary energy storage potential interval. • MnO 2 nanosheet arrays decorate on Fe 2 O 3 driven by MOF. • The M−Fe 2 O 3 @MnO 2 has excellent specific capacitance of 908.5F g −1 . • M−Fe 2 O 3 @MnO 2 //NiCo 2 O 4 delivers a high energy density of 86.8 Wh kg −1 . • Two HSC devices can brighten 25 LEDs for more than 210 min. The development of high-performance anode materials to match the fast-burgeoning cathodes is essential for the fabrication of high-energy–density supercapacitors. Hematite Fe 2 O 3 , with ultra-high theoretical capacitance, has been considered as a promising anode candidate, but the insufficient utilization of the energy storage potential range (mainly in −1.1 V ~ -0.5 V) creates obstacles for further expansion of its electrochemical performance. In this work, a pinecone-like core–shell composite, with vertically grown MnO 2 nanosheet arrays decorated on the M−Fe 2 O 3 prepared via sacrificing the Fe-MOF (MIL-88A) template, was synthesized to achieve the excellent energy storage effect at a wide potential range from −1.1 V to 0.3 V. As adjusting the MnO 2 coating amount to a suitable level, the M−Fe 2 O 3 @MnO 2 composite exhibits a prominent specific capacitance up to 908.5F g −1 as well as excellent cycle stability. Pseudocapacitance analysis interprets the essence of the kinetics process of composite materials in the energy storage process. The hybrid supercapacitor (HSC), assembled with pinecone-like M−Fe 2 O 3 @MnO 2 as the anode and urchin-like NiCo 2 O 4 as the cathode, delivers a high energy density of 86.8 Wh kg −1 at 804.1 W kg −1 . Unsurprisingly, 25 parallel blue LEDs powered by two HSC devices can illuminate for over an astonishing 210 min. This work fabricates a promising anode material for high-energy–density hybrid supercapacitors, and the strategy of complementary energy storage potential provides a novel approach for constructing high-performance energy storage systems.

Fe-Mn Oxides Based Multifunctional Adsorptive/Electrosensing Nanoplatforms: Dynamic Site Rearrangement for Metal Ion Selectivity.

Achieving structural requirements for the exclusive selectivity of adsorbent to a specific metal remains challenging, as certain metal ions show similar adsorptive behaviors and preference toward a given site. We reported the morphology and oxidation state-dependent selectivity manipulating of layered oxides by controlling the dynamic evolution of different adsorptive sites. The computational investigation predicted the site-specific partitioning trends of metal ions at two sites of manganese oxide (MnO2) layers: the lateral edge sites (LESs) and octahedral vacancy sites (OVSs). In contrast to the predominant occupation of the OVSs for other metal ions, the binding of lead (Pb) ions was energetically favored at both the sites. We assembled ultrathin MnO2 nanosheets on the magnetic iron oxides to first enhance the accessibility of the LESs. A sequential ligand-promoted partial reduction of the atomic MnO2 layers induced the edge-to-interlayer migration of Mn atoms to block the nonspecific OVSs and activate the LESs, enabling a superior selectivity to Pb. In addition, the iron oxides helped construct a multifunctional adsorptive/electrosensing platform for Pb regarding their facile magnetic separation and electrochemical activity. Simultaneous selective adsorption and on-site monitoring of Pb(II) were achieved on this nanoplatform, owing to its satisfactory stability and sensitivity without an obvious matrix effect.

Enabling Stable Zn Anode via a Facile Alloying Strategy and 3D Foam Structure

AbstractAqueous zinc‐ion battery (AZIB) has become a promising candidate in grid energy storage due to its low cost, environmental friendliness, and high safety. However, AZIB usually suffers from uncontrollable zinc deposition and dendrite growth as well as hydrogen evolution and passivation on the surface of zinc anode. To address the above issues, a unique 3D Zn alloy foam anode built from Zn–Sn–Pb alloy in 3D Cu foam is constructed by a facile hot dipping method. The proposed 3D Zn alloy anode, through introducing elements Sn and Pb, enhances the hydrogen evolution overpotential, reduces the corrosion current, greatly mitigates the self‐corrosion in the electrolyte, and efficiently inhibits the growth of Zn dendrite during cycling. Importantly, such Zn alloy engineering together with a 3D Cu foam current collector enables highly stable Zn storage properties. The full cell assembled using the proposed 3D Zn alloy anode and MnO2 nanosheet cathode exhibits superior reversible capacity (103.4 mAh g−1) and excellent cycling stability (capacity retention of 87% over 4000 cycles) at 1.8 A g−1.

More from Less but Precise: Industry-relevant Pseudocapacitance by Atomically-precise Mass-loading MnO2 within Multifunctional MXene Aerogel

Ever-increasing mass loading of transition metal oxides (TMOs) yields high pseudocapacitance in laboratory electrochemical capacitors. However, their performance based on whole electrode mass is still far from industry standards. Highly-promising solution based on loading TMOs into 3D porous electrodes causes a yet unresolved challenge to find ways to achieve ultimate energy storage by atomically precisely loading less active material. Inspired by single-atom catalysis, we propose a new “more from less but precise” concept of homogeneously dispersing a common MnO2 TMO via atomic sites to maximize atom redox reaction efficiency for industry-relevant pseudocapacitance. The concept is materialized by multifunctional MXene aerogel with super-hydrophilicity and surface functional groups, which provides 3D atomic nucleation sites to homogeneously load in-situ-formed, covalently-bonded MnO2 nanosheets. The gravimetric capacitance of MnO2 is largely enhanced, yielding superior pseudocapacitance of >400 F/g at > 5 mg/cm2 that is typically achieved at 10 times lower loadings. Outstanding electrode areal capacitance is achieved using 2–3 times less MnO2 mass, demonstrating industry-relevant pseudocapacitance almost twice higher than in state-of-the-art devices. MnO2/MXene//MXene asymmetric supercapacitor shows practically-high energy (~50.1 Wh/kg) and power (~10.0 kW/kg) densities, among the best MnO2 pseudocapacitors. Capacitive-mechanism-controlled redox reactions, rarely achievable in diffusion-controlled porous pseudocapacitive electrodes, are revealed.

Fabrication of 2D/3D hierarchical PBA and derivative electrocatalysts for overall water splitting

Assembling a hierarchical well-defined Prussian blue analogues (PBA) construction is a useful way to take earth-abundant elements into application toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a unique strategy for in-situ grafting three-dimensional (3D) MnFe-PBA cubes on the top of two-dimensional (2D) MnO2 nanosheet arrays (PBA@MnO2) via a facile two-step hydrothermal method with the participation of Ni foam (NF). After experiencing low-temperature pyrolysis in NH3/Ar atmosphere, the above catalysts are transformed into metal-nitride derivatives (N-FeMnNi). Remarkably, when operated in 1.0 M KOH aqueous solution, the as-obtained PBA@MnO2-150/30 (where 150 and 30 represent the hydrothermal temperature (°C) and the concentration of K3Fe(CN)6 (mM) for preparation, respectively) shows the most outstanding OER activity, with an overpotential of 238 mV at 10 mA cm−2. Moreover, N-FeMnNi-130/10 requires an overpotential of 101 mV to reach 10 mA cm−2 for HER. As a result, the two samples are organized to establish a two-electrode cell, with a voltage of only 1.60 V needed to reach 10 mA cm−2. Meanwhile, it can stably work for 30 h without obvious current attenuation. This work provides a brand new perspective for the design of PBA electrocatalysts towards high-efficiency overall water splitting.

A simple signal-on strategy for fluorescent detection of tuberculostatic drug isoniazid based on Ag clusters-MnO2 sheets nanoplatform

As a first-line tuberculostatic drug, isoniazid (INH) plays effective and irreplaceable role in prevention and treatment of tuberculosis. In this work, a rapid and simple signal-on fluorescence approach is established for INH assay by employing a platform composed of silver nanoclusters (AgNCs) and MnO2 nanosheets. In the proposed sensing system, strong red fluorescence of poly (methacrylic acid)-stabilized AgNCs can be greatly quenched after they attach to the surfaces of MnO2 nanosheets. With the addition of INH, MnO2 nanosheets are reduced to Mn2+ and subsequently release the AgNCs, which leads to obvious fluorescence recovery again. Based on this mechanism, highly sensitive detection of INH in the range of 0.8–200 μM is realized (detection limit: 476 nM). The present strategy shows remarkable advantages including simplicity, rapidness, high sensitivity and wide detectable range. This method is also practical and comparable to high-performance liquid chromatography, which can be applied to detect INH in human urine and serum samples as well as pharmaceutical products.

MnO2 nanosheet-mediated target-binding-induced FRET strategy for multiplexed microRNAs detection and imaging in living cells

In the regulatory network, miRNAs play a regulatory role in a cooperative or antagonistic manner. Simultaneous accurate detection and imaging of multiplexed miRNAs in living cells are of great significance for miRNA-associated biological research and disease diagnosis and treatment. Herein, a MnO2 nanosheet-mediated target-binding-induced fluorescence resonance energy transfer (FRET) strategy was developed for detection and imaging of multiplexed miRNAs in living cells. Two pairs of DNA probes (P1-AF 488/P1′-Cy3 and P2-AF 488/P2′-AF 594) contained the complementary sequence to target miRNAs (miRNA-373 and miRNA-96) and labelled with different fluorescence dyes were designed. They were adsorbed onto MnO2 nanosheets by physisorption to form DNA/MnO2 nanocomposite probes. When the DNA/MnO2 nanocomposite probes were taken up by cells, the MnO2 nanosheets were reduced by intracellular glutathione, accompanying the release of DNA probe pairs. Then the DNA probe pairs specifically recognized and combined with miRNA-373 and miRNA-96 to form stable duplexes, respectively, bringing labelled fluorophores into close proximity to occur FRET. Based on this, the simultaneous imaging of miRNA-373 and miRNA-96 in MDA-MB-231 and L02 cells was successfully implemented. The results displayed a higher expression level of target miRNAs in MDA-MB-231 cells compared to L02 cells. The changes in expression levels of miRNA-96 induced by anti-miRNA-96 or mimics in MDA-MB-231 cells could also be monitored. In addition, the ratiometric detections of multiplexed miRNAs were achieved by utilizing the DNA probe pairs. The proposed strategy provides an alternative method for simultaneous accurate detection and imaging of multiplexed miRNAs and has potential application in biomedical applications.

MnO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; nanosheets@Ni-N doped graphene aerogel for Zn-air battery

Zinc-air battery has the advantages of low cost and high theoretical specific capacity (1084 Wh kg−1). The sluggish kinetic of oxygen reduction reaction (ORR) of air cathode limits the reaction rate of zinc-air battery and restricts its practical applications. Moreover, scarce precious metal-based catalysts such as Pt/C are exprensive. Therefore, it is necessary to obtain low-cost ORR catalysts. The conductivity of catalysts affects electron transfer rate in ORR process and consequently affects the catalytic activity. MnO2 has been studied as a promising ORR catalyst for its advantages of low cost, abundant resources and environmental friendliness. However, the poor electronic conductivity of MnO2 limits its applications in ORR related energy storage devices including zinc-air battery. The conductivity can be improved by assembling MnO2 with highly conductive metals and carbon materials. Graphene and its derivatives are often used as substrates of electrochemical materials due to its excellent electronic conductivity and good electrochemical stability. By doping N atoms into graphene skeleton, electronic state can be improved. Doped N atoms make the nearby C atoms become active adsorption sites. Besides, the introduction of oxygen vacancies (OVs) can also improve electronic conductivity of the materials. In this work, a coassembly of MNSs@Ni-NGA showing high ORR catalytic activity was fabricated containing Ni nanoparticles of 10−15 nm in diameter, MnO2 nanosheets (MNSs) of 5−10 nm in sheet thickness at the ratio of exposed surficial to total unit cells of 37.4%, the ratio of OVs to total O atoms of 46.9at% and NGA about 300 nm in wall thickness. Ni nanoparticles, MNSs and NGA all have ORR activity, providing plenty of active sites for ORR. Ni nanoparticles, NGA and OVs improve the conductivity of coassembly and facilitate electron transfer. At the same time, NGA prevents Ni nanoparticles from falling off and aggregating. The big specific surface area (208.0 m2 g−1) of MNSs@Ni-NGA benefits sufficient exposure of active sites. Plenty of mesoporous pores in MNSs@Ni-NGA benefit fast mass transfer during electrochemical process. The basic ORR was characterized by rotating disk electrode (RDE) in electrochemical workstation. Performances of Zn-air battery were studied by electrochemical workstation and LAND battery test system. Through synergistic effects of Ni nanoparticles, MNSs, OVs and NGA, MNSs@Ni-NGA has an onset potential of 0.98 V and a half wave potential of 0.84 V in alkaline electrolyte, close to those of commercial Pt/C (0.98 and 0.85 V). To demonstrate practical application, a Zn-air battery with MNSs@Ni-NGA as air cathode material was assembled, showing an open circuit voltage of 1.53 V, a maximum power density of 114.8 mW cm−2, a specific capacity of 801.9 mAh gZn−1 and a specific energy of 962.3 Wh kgZn−1 (88.8% of the theoretical specific energy), higher than those of commercial Pt/C+IrO2. This work provides a strategy for designing and assembling high performance ORR catalysts with non precious metallic nanoparticles and OVs-containing MnO2 nanostructures for energy storage devices.