Mn-based Prussian blue analogues: Multifunctional nanozymes for hydrogen peroxide detection and photothermal therapy of tumors.

Nanozymes have the advantages of simple synthesis, high stability, low cost and easy recycling, and can be applied in many fields including molecular detection, disease diagnosis and cancer therapy. However, most of the current nanozymes suffer from the defects of low catalytic activity and single function, which limits their sensing sensitivity and multifunctional applications. The development of highly active and multifunctional nanozymes is an important way to realize multidisciplinary applications. In this work, Mn-based Prussian blue analogues (Mn-PBA) and their derived double-shelled nanoboxes (DSNBs) are synthesized by co-precipitation method. The nanobox structure of DSNBs formed by etching Mn-PBA with tannic acid endows Mn-PBA DSNBs with better peroxidase-like activity than Mn-PBA. A colorimetric method for the rapid and sensitive determination of H2O2 is developed using Mn-PBA DSNBs-1.5 as a sensor with a detection limit as low as 0.62 µM. Moreover, Mn-PBA DSNBs-2 has excellent photothermal conversion ability, which can be applied to the photothermal therapy of tumors to inhibit the proliferation of tumor cells without damaging other tissues and organs. This study provides a new idea for the rational design of nanozymes and the expansion of their multi-functional applications in various fields.

Multiresponsive Fluorescence "Turn ON-OFF" Switch on PB@EuW10/SiO2 Composite for Dual Spectral Detection of N2H4 and H2O2.

Herein, a fluorescence "turn ON-OFF" switch model PB@EuW10/SiO2 core@shell composite is designed and fabricated by coating EuW10-containing silica layer on Prussian blue (PB) nanoparticles via a facile method. It is found that the presence of PB can quench the photoluminescence of the composite which arises from EuW10. When hydrazine is mixed with the composite dispersion, PB can be reduced to Prussian white (PW), resulting in the decrease of UV absorption and the appearance of photoluminescence (turn ON). In addition, PW can also be converted back to PB, which is achieved by adding hydrogen peroxide, and the photoluminescence of the composite is quenched again (turn OFF). Thus, the composite is applied for N2H4 and H2O2 detection by fluorescence spectroscopy and UV-vis absorption spectroscopy. Wide linear ranges for N2H4 and H2O2 detection with low detection limits are found for both detection methods on the PB@EuW10/SiO2 core@shell composite. Besides, the color from light blue to colorless of the detection dispersion can also indicate the turn ON-OFF switch for fluorescence. Furthermore, the proposed model can also be extended to other composites.

A nanostructured MoO2/MoS2/MoP heterojunction electrocatalyst for the hydrogen evolution reaction.

Electrocatalytic production of hydrogen from water is considered to be a promising and sustainable strategy. In this work, the low-cost nanostructured MoO2/MoS2/MoP heterojunction is successfully synthesized by phosphorization of the pre-prepared urchin-like MoO2/MoS2 nanospheres as the stable, highly efficient electrocatalysis for the hydrogen evolution reaction (HER). The MoO2/MoS2/MoP-800 (MoO2/MoS2 nanospheres are phosphated at 800 °C) displays a catalytic ability for the HER with an overpotential of 135 mV to achieve 10 mA cm-2 and a Tafel slope of 67 mV dec-1 in 0.5 M H2SO4, which is superior to MoO2/MoS2 nanospheres (200 °C; 24 h), MoO2/MoS2/MoP-700 (MoO2/MoS2 nanospheres are phosphated at 700 °C) and MoO2/MoS2/MoP-900 (MoO2/MoS2 nanospheres are phosphated at 900 °C). Meanwhile, the catalyst exhibits superior properties for HER with an overpotential of 145 mV to achieve 10 mA cm-2 and a Tafel slope of 71 mV dec-1 in 1 M KOH solution. Detailed characterizations reveal that the improved HER performances are significantly related to P-doping and the spherical nanostructure. This work not only provides a low-cost selective for electrocatalytic production of hydrogen, but also serves as a guide to optimize the composition and structure of nanocomposites.

Raspberry-like Pd3Pb alloy nanoparticles: superior electrocatalytic activity for ethylene glycol and glycerol oxidation.

Pd3Pb catalysts are one of the state-of-the-art catalysts for the electrooxidation of alcohols. Herein, raspberry-like Pd3Pb catalysts are synthesized via a simple method. The materials are characterized using various physical techniques. The electrocatalytic behaviors of the products towards the oxidation of ethylene glycol and glycerol are investigated. Electrochemical results show that the raspberry-like Pd3Pb nanostructure produces excellent electrocatalytic activity and stability towards the electrooxidation of ethylene glycol and glycerol in alkaline media, which endows the prepared nanostructure with promising potential in applications like fuel cells.

Incorporating Ni-MOF structure with polypyrrole: enhanced capacitive behavior as electrode material for supercapacitor.

Herein, Ni-MOF sheet incorporated with polypyrrole is fabricated via a simple wet-chemical approach, and the obtained PPy-MOF composite is investigated as an electrode material for supercapacitors. The composite is systematically investigated by a series of characterization studies including X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Besides that, the electrochemical capacitive behaviors of the products are examined by electrochemical measurements. Electrochemical results show varying the ingredient ratio can lead to different electrocapacitive behavior, and PPy-MOF-0.2 is proved to possess the best performance in the investigated recipes. Furthermore, an asymmetric supercapacitor employing PPy-MOF and activated carbon as positive and negative electrodes is also assembled, which exhibits high energy density.

Highly Active PdNi/RGO/Polyoxometalate Nanocomposite Electrocatalyst for Alcohol Oxidation.

A PdNi/RGO/polyoxometalate nanocomposite has been successfully synthesized by a simple wet-chemical method. Characterizations such as transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy are employed to verify the morphology, structure, and elemental composition of the as-prepared nanocomposite. Inspired by the fast-developing fuel cells, the electrochemical catalytic performance of the nanocomposite toward methanol and ethanol oxidation in alkaline media is further tested. Notably, the nanocomposite exhibits excellent catalytic activity and long-term stability toward alcohol electrooxidation compared with the PdNi/RGO and commercial Pd/C catalyst. Furthermore, the electrochemical results reveal that the prepared nanocomposite is attractive as a promising electrocatalyst for direct alcohol fuel cells, in which the phosphotungstic acid plays a crucial role in enhancing the electrocatalytic activities of the catalyst.

Reduced graphene oxide-mediated synthesis of Mn3O4 nanomaterials for an asymmetric supercapacitor cell.

Herein, Mn3O4/reduced graphene oxide composites are prepared via a facile solution-phase method for supercapacitor application. Transmission electron microscopy results reveal the uniform distribution of Mn3O4 nanoparticles on graphene layers. The morphology of the Mn3O4 nanomaterial is changed by introducing the reduced graphene oxide during the preparation process. An asymmetric supercapacitor cell based on the Mn3O4/reduced graphene oxide composite with the weight ratio of 1 : 1 exhibits relatively superior charge storage properties with higher specific capacitance and larger energy density compared with those of pure reduced graphene oxide or Mn3O4. More importantly, the long-term stability of the composite with more than 90.3% capacitance retention after 10 000 cycles can ensure that the product is widely applied in energy storage devices.

Interaction between DNA and microcystin-LR studied by spectra analysis and atomic force microscopy.

Microcystin-LR (MC-LR) is one of the hepatotoxins produced by cyanobacteria in the eutrophicated fresh water. In this work, the minor groove binding mode of MC-LR to plasmid DNA was explored by using UV and fluorescence spectra, and the binding characteristics of MC-LR for plasmid DNA were calculated via the fluorescence quenching of ethidium bromide (EB) and mole ratio method. Furthermore, atomic force microscopy (AFM) was used to observe DNA morphology change in the presence of MC-LR. With the increasing concentration of MC-LR, circle DNA strands twined gradually to rod condensates. The possible reason for the condensation might be the masking of the electrostatic repulsion between DNA double strands by MC-LR. The present study might provide useful information for the pathopoiesis mechanism of MC-LR. More, because the condensation of DNA could affect the progresses of gene expression and protein transcription, it may implicate another trend to explore the nosogenesis of MC-LR.

Facile synthesis of urchin-like gold submicrostructures for nonenzymatic glucose sensing.

Urchin-like gold submicrostructures (UGS) were successfully synthesized by a seed-mediated method which is quite facile and does not need any template or surfactant agent. The effect of the added silver seeds on the morphology and size of final products were investigated, and a possible growth mechanism of crystals was proposed. Electrochemical characterization indicated that these UGS have better catalytic activity for the glucose oxidation compared with flower-like gold submicrostructures (FGS), which could be ascribed to its higher surface to volume ratio. An electrochemical nonenzymatic glucose sensor was fabricated simply by casting the UGS and Nafion solution onto glass carbon electrode. This sensor displays a wide linear range from 0.2 to 13.2mM with a high sensitivity of 16.8 µA mM(-1)cm(-2), and a detection limit of 10 µM. The unique properties of this sensor, such as fast response and well stability reveal the potential application of the UGS based materials in nonenzymatic detection of glucose.

Carbon nanotube/raspberry hollow Pd nanosphere hybrids for methanol, ethanol, and formic acid electro-oxidation in alkaline media.

In this paper, raspberry hollow Pd nanospheres (HPNs)-decorated carbon nanotube (CNT) was developed for electro-oxidation of methanol, ethanol, and formic acid in alkaline media. The electrocatalyst was fabricated simply by attaching HPNs onto the surface of CNT which had been functionalized by polymer wrapping. The as-prepared HPN-CNTs (CHPNs) were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The increasing interest and intensive research on fuel cell inspire us to investigate the electrocatalytic properties of the prepared nanostructures. Besides that, previous reports about alkaline other than acidic media could supply a more active environment guide us to examine the electrocatalytic properties in alkaline electrolyte. It is found that this novel hybrid electrocatalyst exhibits excellent electrocatalytic properties and can be further applied in fuel cells, catalysts, and sensors.

Novel nonenzymatic hydrogen peroxide sensor based on iron oxide-silver hybrid submicrospheres.

Fe(3)O(4)-Ag hybrid submicrosphere was synthesized and developed as hydrogen peroxide sensor in this study. The hybrid sphere was fabricated via a two-step route, and proved by characterizations such as TEM, SEM, EDX, and XPS. Recent studies of hydrogen peroxide sensor based on silver nanoparticles inspired us to study the electrocatalytic property of the as-prepared submicrosphere. Though the Ag amount is quite little in the hybrid spheres, the electrochemical sensor constructed by the hybrid spheres exhibited fast, stable and well-defined electrocatalytic activity towards H(2)O(2) reduction, which should be the contribution of the combination of Fe(3)O(4) and Ag. The detection limit of H(2)O(2) was also found to be 1.2microM, which was lower than some enzyme-based biosensors.

Type I collagen-mediated synthesis of noble metallic nanoparticles networks and the applications in Surface-Enhanced Raman Scattering and electrochemistry.

In this paper, we demonstrated an effective environmentally friendly synthesis route to prepare noble metallic (Au, Ag, Pt and Pd) nanoparticles (NPs) networks mediated by type I collagen in the absence of any seeds or surfactants. In the reactions, type I collagen served as stabilizing agent and assembly template for the synthesized metallic NPs. The hydrophobic interaction between collagen and mica interface as well as the hydrogen bonds between inter- and intra-collagen molecules play important roles in the formation of collagen-metallic NPs networks. The noble metallic NPs networks have many advantages in the applications of Surface-Enhanced Raman Scattering (SERS) and electrochemistry detection. Typically, the as-prepared Ag NPs networks reveal great Raman enhancement activity for 4-ATP, and can even be used to detect low concentration of DNA base, adenine, without any label step. Furthermore, the cyclic voltammograms showed Pt NPs networks have good electrocatalytic ability for the reduction of O(2).

Influence of polyelectrolyte on DNA-RecA nucleoprotein filaments: poly-L-lysine used as a model.

RecA of Escherichia coli and its active nucleoprotein filaments with DNA are important for the genomic integrity and the genetic diversity. The formation of the DNA-RecA nucleoprotein filaments is a complex multiple-step process and can be affected by many factors. In this work, the effects of poly-L-lysine (PLL) on the DNA-RecA nucleoprotein filaments are investigated in vitro by agarose gel electrophoresis and atomic force microscopy (AFM). The observed morphologies vary with the concentration, the length, and the addition order of PLL. These distinctions provide information for the conformation change of DNA and the binding sites of RecA protein in the formation process of nucleoprotein filaments. Besides that, the comparison displays the effect of cationic polyelectrolyte on both inhibition and destabilization of the DNA-RecA nucleoprotein filaments. The current study provides valuable insights for pharmacologic studies and gene delivery.

Atomic force microscopy and surface-enhanced Raman scattering detection of DNA based on DNA-nanoparticle complexes.

We report a simple method for the label-free detection of double-stranded DNA using surface-enhanced Raman scattering (SERS). We prepared cetyltrimethylammonium bromide (CTAB)-capped silver nanoparticles and a DNA-nanoparticle complex by adding silver nanoparticles to lambda-DNA solutions. In the present study, the utilization of CTAB-capped silver nanoparticles facilitates the electrostatic interaction between DNA molecules and silver nanoparticles; at the same time, the introduction of DNA avoids adding aggregating agent for the formation of nanoparticle aggregates to obtain large enhancement of DNA, because the DNA acts as both the probe molecules and aggregating agent of Ag nanoparticles. Atomic force microscopy (AFM) studies show that the morphology of DNA-Ag nanoparticle complexes seems to be determined by the concentrations of the DNA and the nanoparticles. Surface-enhanced Raman scattering (SERS) studies show that the morphology of the complexes plays a significant role in the intensity of SERS signals of DNA, and the best signal enhancement of DNA can be obtained by fine-tuning the experimental parameters. The SERS spectrum affords important structural information about the bases, phosphate backbone, and the conformation of DNA after mixing the DNA solutions with the Ag sol.

Surface-relevant regulable DNA toroids induced by dopamine.

Dopamine (2-(3,4-dihydroxyphenyl)ethylamine) is known as a natural chemical neurotransmitter and is also a cytotoxic and genotoxic molecule for cell apoptosis. In this work, the interaction of DNA with dopamine was investigated. Though the electrostatic interaction of DNA and dopamine was weak in aqueous solution, dopamine condensed circular pBR322 DNA into toroids on the mica surface cooperatively with ethanol. The formed DNA toroids came from the shrinking of DNA that was driven by ethanol-enhanced DNA-dopamine electrostatic interaction. The size of the DNA toroids could be modulated by varying the concentration of dopamine. This study offers useful information about the DNA condensation induced by monovalent cations and the sample preparation for AFM measurement and application. On the other hand, this work provides the potential strategies to prepare morphology and size controllable DNA condensates, which have valuable applications in gene transfection and nanotechnology.

DNA-templated gold nanoparticles formation.

The interaction between HAuCl4 and DNA has enabled creation of DNA-templated gold nanoparticles without formation of large nanoparticles. It was found that spheral DNA-HAuCl4 hybrid of 8.7 nm in diameter, flower-like DNA-HAuCl4 hybrid, nanoparticles chains and nanoparticles network of DNA-HAuCl4 hybrid could be obtained by varying the reaction conditions, including DNA concentration and reaction temperature. The intermediate product was investigated by shortening the reaction time of DNA and HAuCl4, and the obtained nanoparticles preserved a small DNA segment, which indicated that the reaction between DNA and HAuCl4 had a process. The addition of reduction reagent resulted in DNA-templated gold nanoparticles and nanoflowers, respectively. UV-vis absorption spectra were used to characterize the DNA-HAuCl4 hybrid and the gold nanostructures templated on DNA, and XPS spectra were used to compare the composition of DNA-Au(III) complex and gold nanoparticles. AFM and TEM results revealed that the spheral gold nanoparticles of about 11 nm in size and flower-like gold nanoparticles were formed after the addition of NaBH4.

Fabrication, characterization, and application in surface-enhanced Raman spectrum of assembled type-I collagen-silver nanoparticle multilayered films.

In this paper, we report a facile method for the fabrication of type-I collagen-silver nanoparticles (Ag NPs) multilayered films by utilizing type-I collagen as a medium. These samples were characterized by UV-vis spectra photometer, atomic force microscopy, scanning electron microscopy, and Fourier transform IR spectrum. Experimental results show that collagen molecules serve as effective templates to assemble Ag NPs into multilayer films. These samples exhibit high surface-enhanced Raman scattering (SERS) enhancement abilities. For example, EF(nu(cc)) (EF means enhancement factor) at 1592 cm(-1) in the SERS spectrum of 4-aminothiophenol on seven-layered substrates was calculated to be 1.81 x 10(5), which is larger than that reported in several literatures. The EFs increased as the layer number of multilayer films increases.

Atomic force microscopic study of low temperature induced disassembly of RecA-dsDNA filaments.

The assembly and disassembly of RecA-DNA nucleoprotein filaments on double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA) are important steps for homologous recombination and DNA repair. The assembly and disassembly of the nucleoprotein filaments are sensitive to the reaction conditions. In this work, we investigated different morphologies of the formed nucleoprotein filaments at low temperature under different solution conditions by atomic force microscopy (AFM). We found that low temperature and long keeping time could induce the incomplete disassembly of the formed nucleoprotein filaments. In addition, when the formed filaments were kept at -20 degrees C for 20 h with 1,4-dithiothreitol (DTT), the integrated filaments disassembled. It was similar to the case under the same condition without anything added. However, when glycerol was used as a substitute for DTT, there was no obvious disassembly at the same condition. Oppositely, when the formed filaments were kept at 4 degrees C for 20 h, the disassembly with additional DTT was not as obvious as the case at -20 degrees C for 20 h, whereas the case with additional glycerol disassembled. The experiments indicated the effect of cold denaturation on the interaction of DNA and RecA. Meanwhile, the study of these phenomena can supply guidelines for the property and stability of RecA as well as the relevant roles of influencing factors to RecA and DNA in further theoretical studies.