A cobalt oxyhydroxide nanoflake-based nanoprobe for the sensitive fluorescence detection of T4 polynucleotide kinase activity and inhibition

Phosphorylation of nucleic acids with 5'-OH termini catalyzed by polynucleotide kinase (PNK) is an inevitable process and has been implicated in many important cellular events. Here, we found for the first time that there was a significant difference in the adsorbent ability of cobalt oxyhydroxide (CoOOH) nanoflakes between single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), which resulted in the fluorescent dye-labeled dsDNA still retaining strong fluorescence emission, while the fluorescence signal of ssDNA was significantly quenched by CoOOH nanoflakes. Based on this discovery, we developed a CoOOH nanoflake-based nanoprobe for the fluorescence sensing of T4 PNK activity and its inhibition by combining it with λ exonuclease cleavage reaction. In the presence of T4 PNK, dye-labeled dsDNA was phosphorylated and then cleaved by λ exonuclease to generate ssDNA, which could adsorb on the CoOOH nanoflakes and whose fluorescence was quenched by CoOOH nanoflakes. Due to the high quenching property of CoOOH nanoflakes as an efficient energy acceptor, a sensitive and selective sensing approach with satisfactory performance for T4 PNK sensing in a complex biological matrix has been successfully constructed and applied to the screening of inhibitors. The developed approach may potentially provide a new platform for further research, clinical diagnosis, and drug discovery of nucleotide kinase related diseases.

A completely controlled sphere-to-bilayer micellar transition: the molecular mechanism and application on the growth of nanosheets

The combination of a simple modification of the sample addition method to generate a sort of continuously accumulated external stimulation with only minute increments in amplitude and the introduction of probe molecules (herein aniline) within the micelle allow the direct continuous in situ spectroscopic monitoring of possible micellar transitions. In this way, a sphere-to-ellipsoid and further an ellipsoid-to-bilayer micellar transition of sodium dodecyl sulfate (SDS) induced by camphor sulfuric acid (CSA) is observed to experience four stages in the time sequence: (i) the accumulated protons released from CSA in the hydration layer of the micelle stimulate the rearrangement of SDS micelles; (ii) the micelles transform into ellipsoidal shapes as evidenced by the characteristic chemical shift anisotropy and the corresponding molecular dynamic properties from probe molecules; (iii) further protonation of aniline induces the micelle to turn into lamellar structures; (iv) aniline is freed from the micelle while leaving the SDS bilayers undistorted. Moreover, polyaniline nanosheets incorporating SDS bilayers in sandwich structures, which can display excellent capacitive behavior at relatively high current densities for the fabricated supercapacitors, are prepared from the aniline oriented by the bending energy of the SDS bilayers.

Biocompatible multilayer capsules engineered with a graphene oxide derivative: synthesis, characterization and cellular uptake

Graphene-based capsules have strong potential for a number of applications, including drug/gene delivery, tissue engineering, sensors, catalysis and reactors. The ability to integrate graphene into carrier systems with three-dimensional (3D) geometry may open new perspectives both for fundamental tests of graphene mechanics and for novel (bio)technological applications. However, the assembly of 3D complexes from graphene or its derivatives is challenging because of its poor stability under biological conditions. In this work, we attempted to integrate a layer of graphene oxide derivative into the shell of biodegradable capsules by exploiting a facile layer-by-layer (LbL) protocol. As a first step we optimized the LbL protocol to obtain colloidal suspensions of isolated capsules embedding the graphene oxide derivative. As a following step, we investigated in detail the morphological properties of the hybrid capsules, and how the graphene oxide derivative layer influences the porosity and the robustness of the multilayer composite shells. Finally, we verified the uptake of the capsules modified with the GO derivative by two cell lines and studied their intracellular localization and biocompatibility. As compared to pristine capsules, the graphene-modified capsules possess reduced porosity, reduced shell thickness and a higher stability against osmotic pressure. They show remarkable biocompatibility towards the tested cells and long-term colloidal stability and dispersion. By combining the excellent mechanical properties of a graphene oxide derivative with the high versatility of the LbL method, robust and flexible biocompatible polymeric capsules with novel characteristics have been fabricated.

Prospects of Supercritical Fluids in Realizing Graphene-Based Functional Materials

Supercritical-fluids science and technology predate all the approaches that are currently established for graphene production by several decades in advanced materials design. However, it has only recently been proposed as a plausible approach for graphene processing. Since then, supercritical fluids have emerged into contention as an alternative to existing technologies because of their scalability and versatility in processing graphene materials, which include composites, aerogels, and foams. Here, an overview is presented of such materials prepared through supercritical fluids from an advanced materials science standpoint, with a discussion on their fundamental properties and technological applications. The benefits of supercritical-fluid processing over conventional liquid-phase processing are presented. The benefits include not only better performances for advanced applications but also environmental issues associated with the synthesis process. Nevertheless, the limitations of supercritical-fluid processing are also stressed, along with challenges that are still faced toward the achievement of the great expectations from graphene materials.

Mesoporous Hybrid Shells of Carbonized Polyaniline/Mn2O3 as Non-Precious Efficient Oxygen Reduction Reaction Catalyst

Mesoporous hybrid shells of carbonized polyaniline (CPANI)/Mn2O3 with well-controlled diameter and high surface area have been synthesized through surface protected calcination processes. Originating from polystyrene template, PANI, MnO2, and SiO2 were sequentially loaded, followed by template removal and calcination, resulting in the desired CPANI/Mn2O3 hybrid shells. The introduction of SiO2 shell was established to play the determining role in maintaining the configuration during calcination process under high temperature. The CPANI/Mn2O3 hybrid shells showed outstanding electrocatalytic activity toward oxygen reduction reaction (ORR), with the onset potential at +0.974 V (versus RHE), the specific current at 60.8 mA/mg, and an overall quasi 4-electron transfer, which are comparable to those of the benchmark Pt/C. The remarkable ORR performance was attributed to the high specific surface area, the surface oxidation state of Mn, and composition-codependent behavior.

A sensitive impedimetric DNA biosensor for the determination of the HIV gene based on graphene-Nafion composite film

An impedimetric HIV-1 gene biosensor has been developed based on graphene-Nafion composite film. The biosensor was fabricated by adsorbing the single-stranded DNA (ssDNA) on graphene-Nafion modified on the surface of glassy carbon electrode via the π-π* stacking interactions. As the negative ssDNA and the steric hindrance, the electron transfer resistance of the electrodes toward the [Fe(CN)₆]^3-/4 redox couple was difficult, the electron transfer resistance value increased. In the measurement of HIV gene, ssDNA probe with the target DNA to form double-stranded DNA (dsDNA), the formation of helix induced dsDNA to release from the surface of the biosensor. The decrease in the electron transfer resistance was in logarithmically direct proportion to the concentration of HIV-1 gene over a range from 1.0×10^-13 to 1.0×10^-10M. The detection limit of this sensor was 2.3×10^-14M. It was found that Nafion could not only stabilize graphene but also increase the dispersion of graphene. The results demonstrate that this graphene-Nafion biosensor possesses good selectivity, acceptable stability and reproducibility for HIV-1 gene detection.

Nanostructured Materials for Room-Temperature Gas Sensors

Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

Preparation of Three-Dimensional Graphene Foams Using Powder Metallurgy Templates

A simple and scalable method which combines traditional powder metallurgy and chemical vapor deposition is developed for the synthesis of mesoporous free-standing 3D graphene foams. The powder metallurgy templates for 3D graphene foams (PMT-GFs) consist of particle-like carbon shells which are connected by multilayered graphene that shows high specific surface area (1080 m(2) g(-1)), good crystallization, good electrical conductivity (13.8 S cm(-1)), and a mechanically robust structure. The PMT-GFs did not break under direct flushing with DI water, and they were able to recover after being compressed. These properties indicate promising applications of PMT-GFs for fields requiring 3D carbon frameworks such as in energy-based electrodes and mechanical dampening.

Are vacuum-filtrated reduced graphene oxide membranes symmetric?

Graphene or reduced graphene oxide (rGO) membrane-based materials are promising for many advanced applications due to their exceptional properties. One of the most widely used synthesis methods for rGO membranes is vacuum filtration of graphene oxide (GO) on a filter membrane, followed by reduction, which shows great advantages such as operational convenience and good controllability. Despite vacuum-filtrated rGO membranes being widely used in many applications, a fundamental question is overlooked: are the top and bottom surfaces of the membranes formed at the interfaces with air and with the filter membrane respectively symmetric or asymmetric? This work, for the first time, reports the asymmetry of the vacuum-filtrated rGO membranes and discloses the filter membranes' physical imprint on the bottom surface of the rGO membrane, which takes place when the filter membrane surface pores have similar dimension to GO sheets. This result points out that the asymmetric surface properties should be cautiously taken into consideration while designing the surface-related applications for GO and rGO membranes.

N-Doped Ordered Mesoporous Carbon Originated from a Green Biological Dye for Electrochemical Sensing and High-Pressure CO2 Storage

Herein, a series of nitrogen-doped ordered mesoporous carbons (NOMCs) with tunable porous structure were synthesized via a hard-template method with a green biological dye as precursor, under various carbonization temperatures (700-1100 °C). Compared with the ordered mesoporous silica-modified and unmodified electrodes, the use of electrodes coated by NOMCs (NOMC-700-NOMC-1100) resulted in enhanced signals and well-resolved oxidation peaks in electrocatalytic sensing of catechol and hydroquinone isomers, attributable to NOMCs' open porous structures and increased edge-plane defect sites on the N-doped carbon skeleton. Electrochemical sensors using NOMC-1000-modified electrode were fabricated and proved feasible in tap water sample analyses. The NOMCs were also used as sorbents for high-pressure CO2 storage. The NOMC with the highest N content exhibits the best CO2 absorption capacities of 800.8 and 387.6 mg/g at 273 and 298 K (30 bar), respectively, which is better than those of other NOMC materials and some recently reported CO2 sorbents with well-ordered 3D porous structures. Moreover, this NOMC shows higher affinity for CO2 than for N2, a benefit of its higher nitrogen content in the porous carbon framework.

Nano-Bioelectronics

Nano-bioelectronics represents a rapidly expanding interdisciplinary field that combines nanomaterials with biology and electronics and, in so doing, offers the potential to overcome existing challenges in bioelectronics. In particular, shrinking electronic transducer dimensions to the nanoscale and making their properties appear more biological can yield significant improvements in the sensitivity and biocompatibility and thereby open up opportunities in fundamental biology and healthcare. This review emphasizes recent advances in nano-bioelectronics enabled with semiconductor nanostructures, including silicon nanowires, carbon nanotubes, and graphene. First, the synthesis and electrical properties of these nanomaterials are discussed in the context of bioelectronics. Second, affinity-based nano-bioelectronic sensors for highly sensitive analysis of biomolecules are reviewed. In these studies, semiconductor nanostructures as transistor-based biosensors are discussed from fundamental device behavior through sensing applications and future challenges. Third, the complex interface between nanoelectronics and living biological systems, from single cells to live animals, is reviewed. This discussion focuses on representative advances in electrophysiology enabled using semiconductor nanostructures and their nanoelectronic devices for cellular measurements through emerging work where arrays of nanoelectronic devices are incorporated within three-dimensional cell networks that define synthetic and natural tissues. Last, some challenges and exciting future opportunities are discussed.

Controlled graphene oxide assembly on silver nanocube monolayers for SERS detection: dependence on nanocube packing procedure

Hybrid graphene oxide/silver nanocubes (GO/AgNCs) arrays for surface-enhanced Raman spectroscopy (SERS) applications were prepared by means of two procedures differing for the method used in the assembly of the silver nanocubes onto the surface: Langmuir-Blodgett (LB) transfer and direct sequential physisorption of silver nanocubes (AgNCs). Adsorption of graphene oxide (GO) flakes on the AgNC assemblies obtained with both procedures was monitored by quartz crystal microbalance (QCM) technique as a function of GO bulk concentration. The experiment provided values of the adsorbed GO mass on the AgNC array and the GO saturation limit as well as the thickness and the viscoelastic properties of the GO film. Atomic force microscopy (AFM) measurements of the resulting samples revealed that a similar surface coverage was achieved with both procedures but with a different distribution of silver nanoparticles. In the GO covered LB film, the AgNC distribution is characterized by densely packed regions alternating with empty surface areas. On the other hand, AgNCs are more homogeneously dispersed over the entire sensor surface when the nanocubes spontaneously adsorb from solution. In this case, the assembly results in less-packed silver nanostructures with higher inter-cube distance. For the two assembled substrates, AFM of silver nanocubes layers fully covered with GO revealed the presence of a homogeneous, flexible and smooth GO sheet folding over the silver nanocubes and extending onto the bare surface. Preliminary SERS experiments on adenine showed a higher SERS enhancement factor for GO on Langmuir-Blodgett films of AgNCs with respect to bare AgNC systems. Conversely, poor SERS enhancement for adenine resulted for GO-covered AgNCs obtained by spontaneous adsorption. This indicated that the assembly and packing of AgNCs obtained in this way, although more homogeneous over the substrate surface, is not as effective for SERS analysis.

Hierarchical core–shell structure of ZnO nanotube/MnO2 nanosheet arrays on a 3D graphene network as a high performance biosensing platform

A hierarchical core–shell structure composed of ZnO nanotubes/MnO₂ nanosheets was fabricated via a two-step electrochemical deposition procedure on the surface of a 3D graphene network (3DGN) as a free-standing monolithic electrode.

Facile synthesis of gold–platinum dendritic nanostructures with enhanced electrocatalytic performance for the methanol oxidation reaction

Gold–platinum dendritic nanoparticles prepared through a surfactant-free wet-chemical route exhibited good catalytic performance for the methanol oxidation reaction.

Recent development of carbon electrode materials and their bioanalytical and environmental applications

New synthetic approaches, materials, properties, electroanalytical applications and perspectives of carbon materials are presented.

Engineered nanomembranes for smart energy storage devices

This review presents recent progress in engineered tubular and planar nanomembranes for smart energy storage applications, especially related to the investigation of fundamental electrochemical kinetics.

Constructing nitrogen-doped nanoporous carbon/graphene networks as promising electrode materials for supercapacitive energy storage

Nitrogen-doped nanoporous carbon/graphene networks have been constructed and show a larger specific capacitance than that of NPCs and rGO.

Hybrid SnO2–Co3O4 nanocubes prepared via a CoSn(OH)6 intermediate through a sonochemical route for energy storage applications

A cubic-like nanostructured SnO₂–Co₃O₄ hybrid was sonochemically synthesized via CoSn(OH)₆ nanocubes as an intermediate for supercapacitor application.

Synergistic effect of graphene and multi-walled carbon nanotubes composite supported Pd nanocubes on enhancing catalytic activity for electro-oxidation of formic acid

Synergistic effect of rGO/MWCNTs composite supported Pd nanocubes enhanced the performance of direct formic acid fuel cells.

Towards high-efficiency nanoelectrocatalysts for oxygen reduction through engineering advanced carbon nanomaterials

We summarize and discuss recent developments of different-dimensional advanced carbon nanomaterial-based noble-metal-free high-efficiency oxygen reduction electrocatalysts, including heteroatom-doped, transition metal-based nanoparticle-based, and especially iron carbide (Fe₃C)-based carbon nanomaterial composites.

Direct delamination of graphite ore into defect-free graphene using a biphasic solvent system under pressurized ultrasound

The study reported herein describes for the first time a method for producing defect-free graphene directly from its mineral ore.

Half-cell and full-cell applications of horizontally aligned reduced oxide graphene/V2O5 sheets as cathodes for high stability lithium-ion batteries

2D hybrid sheets of V₂O₅ and reduced graphene oxide (rGO/V₂O₅) have been synthesized using a hydrothermal method.

Characterization of a graphene oxide/poly(acrylic acid) nanocomposite by means of molecular dynamics simulations

Graphene oxide/poly(acrylic acid) nanocomposite: static, dynamic, thermal properties and hydrogen bonding, as studied by molecular dynamics simulations.

Preparation of three-dimensional free-standing nano-LiFePO4/graphene composite for high performance lithium ion battery

We synthesized a 3D nano-LiFePO₄/graphene composite by a facile in situ hydrothermal method and it shows excellent performance in LIBs.

Graphene oxide: strategies for synthesis, reduction and frontier applications

In this review article, we describe a general introduction to GO, its synthesis, reduction and some selected frontier applications. Its low cost and potential for mass production make GO a promising building block for functional hybrid materials.

Preparation of porous graphene oxide/hydrogel nanocomposites and their ability for efficient adsorption of methylene blue

Porous nanocomposite hydrogels were prepared using CaCO₃ particles as solid porogens.

Emergence of fluorescence in boron nitride nanoflakes and its application in bioimaging

Hexagonal boron nitride (h-BN) nanoflakes show fluorescence and can be used for bio-imaging.

In situ synthesis of pristine-graphene/Ag nanocomposites as highly sensitive SERS substrates

In this paper, we proposed a simple in situ method for the synthesis of pristine-graphene/Ag nanocomposites by chemical reduction of Ag ions in a N-methyl pyrrolidone solution in which pristine-graphene had been homogeneously dispersed.

Ultrafine CoP Nanoparticles Supported on Carbon Nanotubes as Highly Active Electrocatalyst for Both Oxygen and Hydrogen Evolution in Basic Media

The development of low-cost and highly active electrocatalysts for two half reactions: H2 and O2 evolution reactions (HER and OER), is still a huge challenge to realize water splitting. Herein, we report that CoP nanoparticles (NPs) can act as a bifunctional catalyst for both HER and OER. Particularly, ultrafine CoP NPs decorated on N-doped multiwalled carbon nanotube (MWCNT) exhibit remarkable catalytic performance for OER in 0.1 M NaOH aqueous solution, with a low onset overpotential of 290 mV, a Tafel slope of 50 mV dec(-1), an overpotential (η) of 330 mV at 10 mA cm(-2), and approximately 100% Faradaic efficiency, paralleling the performance of state-of-the-art Co-based OER catalysts including Co3O4, CoSe2, and Co-Pi. The hybrid catalyst is capable of maintaining a high catalytic current density for at least 10 h without any loss of catalytic activity. Meanwhile, the noble-metal-free catalyst also shows good activity and duarability for HER under the same basic condition.

Recent advance in fabricating monolithic 3D porous graphene and their applications in biosensing and biofuel cells

Graphene shows great potential in biosensing and bioelectronics. To facilitate graphene's applications and enhance its performance, recently, three-dimensional (3D) graphene-based materials especially free-standing porous graphene with tunable pore size and void space, have attracted increasing attention for bio-related applications owing to their special features. 3D graphene usually shows the following merits such as an interconnected porous network, a high electronic conductivity, a large active surface area, good chemical/thermal stability and can be more easily handled compared with dispersed graphene sheets. With modified surface properties, graphene can also be bio-friendly. These properties make 3D graphene a perfect candidate as high-performance electrode materials in bioelectronics devices. In this review, we discuss recent advance in fabricating monolithic 3D graphene and their applications in biosensing and biofuel cells.

Observation of the retarded transportation of a photogenerated hole on epitaxial graphene

Graphene is usually adopted as an assistant additive for catalysts in photocatalytic processes, because of its ability to accelerate the separation of photogenerated charge carriers. To elucidate the mechanism, hydrogen peroxide is adopted to convert the O2(-)˙ active species into OH˙ for degradation of an organic dye. If the pH value is less than 7, the concentration of the OH˙ species can be reduced more quickly with the addition of graphene than without, because negatively charged electrons can be transported quickly on graphene. If the pH value is larger than 7, the concentration of OH˙ can be promoted by the catalyst SiC with photogenerated h(+) release and reaction with OH(-), however the concentration is reduced if the SiC catalyst is covered by a graphene sheet, as it retards h(+) release from the SiC substrate. Our findings have provided a certification for the role of graphene in photo-catalytic processes.