Electrochemical hydrogen sulfide biosensors.

The measurement of sulfide, especially hydrogen sulfide, has held the attention of the analytical community due to its unique physiological and pathophysiological roles in biological systems. Electrochemical detection offers a rapid, highly sensitive, affordable, simple, and real-time technique to measure hydrogen sulfide concentration, which has been a well-documented and reliable method. This review details up-to-date research on the electrochemical detection of hydrogen sulfide (ion selective electrodes, polarographic hydrogen sulfide sensors, etc.) in biological samples for potential therapeutic use.

Tunable Fabrication of Molybdenum Disulfide Quantum Dots for Intracellular MicroRNA Detection and Multiphoton Bioimaging.

Molybdenum disulfide (MoS2 ) quantum dots (QDs) (size <10 nm) possess attractive new properties due to the quantum confinement and edge effects as graphene QDs. However, the synthesis and application of MoS2 QDs has not been investigated in great detail. Here, a facile and efficient approach for synthesis of controllable-size MoS2 QDs with excellent photoluminescence (PL) by using a sulfuric acid-assisted ultrasonic route is developed for this investigation. Various MoS2 structures including monolayer MoS2 flake, nanoporous MoS2 , and MoS2 QDs can be yielded by simply controlling the ultrasonic durations. Comprehensive microscopic and spectroscopic tools demonstrate that the MoS2 QDs have uniform lateral size and possess excellent excitation-independent blue PL. The as-generated MoS2 QDs show high quantum yield of 9.65%, long fluorescence lifetime of 4.66 ns, and good fluorescent stability over broad pH values from 4 to 10. Given the good intrinsic optical properties and large surface area combined with excellent physiological stability and biocompatibility, a MoS2 QDs-based intracellular microRNA imaging analysis system is successfully constructed. Importantly, the MoS2 QDs show good performance as multiphoton bioimaging labeling. The proposed synthesis strategy paves a new way for facile and efficient preparing MoS2 QDs with tunable-size for biomedical imaging and optoelectronic devices application.

Filtration-wet transferred transparent conducting films of mm long carbon nanotubes grown using water-assisted chemical vapor deposition.

Transparent conducting films (TCF) made up from carbon nanotubes (CNTs) have a tremendous potential in replacing the indium tin oxide films. Compare to single wall CNTs multiwall CNTs are more metallic and are more suitable candidate for the TCF. In this letter we report the use of selectively grown mm-scale, few-wall, vertically aligned CNTs for the fabrication of TCF. Water-assisted chemical vapor deposition was used to grow the mm-scale CNTs within short growth time. A special post-growth water-vapor treatment allowed us to remove the catalyst-free CNT forest very easily from the substrate and use it for the further process. A filtration-wet transfer process was used to form the TCF. The TCF shows sheet resistance of 228 omega/sq. at 72% transparency (at 550 nm). The ratio of optical conductivity to dc conductivity was observed in between 0.21 to 0.25 for below 80% transmission.

Revealing the Role of Hydrogen in Electron-Doping Mottronics for Strongly Correlated Vanadium Dioxide.

Hydrogen-associated electron-doping Mottronics for d-band correlated oxides (e.g., VO2) opens up a new paradigm to regulate the electronic functionality via directly manipulating the orbital configuration and occupancy. Nevertheless, the role of hydrogen in the Mottronic transition of VO2 is yet unclear because opposite orbital reconfigurations toward either the metallic or highly insulating states were both reported. Herein, we demonstrate the root cause for such hydrogen-induced multiple electronic phase transitions by 1H quantification using nuclear reaction analysis. A low hydrogenation temperature is demonstrated to be vital in achieving a large hydrogen concentration (nH ≈ 1022 cm-3) that further enhances the t2g orbital occupancy to trigger electron localizations. In contrast, elevating the hydrogenation temperatures surprisingly reduces nH to ∼1021 cm-3 but forms more stable metallic H0.06VO2. This leads to the recognition of a weaker hydrogen interaction that triggers electron localization within VO2 via Mottronically enhancing the orbital occupancies.

Aerogels from copper (II)-cellulose nanofibers and carbon nanotubes as absorbents for the elimination of toxic gases from air.

A novel deodorizer that is capable of selectively eliminating the odorous chemicals, such as ammonia, trimethylamine, hydrogen sulfide and methyl mercaptan, is described. The deodorizer is a nanostructured aerogel by nature, consisting of 2,2-6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofibrils (CNF), transition metal divalent cations (M2+), and multi-walled carbon nanotubes (CNT) as the constitutive elements. CNF are firstly mixed with M2+ (M2+, in this paper, typifies Ni2+, Co2+ and Cu2+) to form CNF-M2+ complexes, monodispersed CNT is then mixed to prepare CNT/CNF-M2+ waterborne slurries; CNT/CNF-M2+ hybridized aerogels are finally obtained via freezing-drying of the CNT/CNF-M2+ waterborne slurries. The CNT/CNF-M2+ aerogels are a foam-like structure consisting of CNF and CNT as backbones and M2+ as linkers. The aerogels show higher capabilities (in comparison with activated carbon) for selectively adsorbing ammonia, trimethylamine, hydrogen sulfide and methyl mercaptan. Computing simulations suggest a theoretical conclusion that the odorous chemicals are absorbed in a preferring manner of bimolecular absorptions via the M2+ moieties. The CNT/CNF-M2+ hybridized aerogels are lightweight, eco-friendly, and easy to produce in industrial scales. Our new finding, as is described in this paper, demonstrates potential applications of the TEMPO-oxidized CNF to the field of deodorizations.

A finger-jointing model for describing ultrastructures of cellulose microfibrils.

In this paper, we propose a finger-jointing model to describe the possible ultrastructures of cellulose microfibrils based on new observations obtained through heating of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanofibrils (CNFs) in saturated water vapor. We heated the micrometers-long TEMPO-CNFs in saturated water vapor (≥ 120 °C, ≥ 0.2 MPa) and observed a surprising fact that the long TEMPO-CNFs unzipped into short (100 s of nanometers long) fibers. We characterized the heated TEMPO-CNFs using X-ray diffraction (XRD) and observed the XRD patterns were in consistent with Iß. We observed also jointed ultrastructures on the heated TEMPO-CNFs via high-resolution transmission electron microscopy (HR-TEM). Thus we concluded that cellulose microfibrils are not seamlessly long structures, but serial jointed structures of shorter blocks. Polysaccharide chains of the short blocks organized in Iß. The jointed region can be either Iα or amorphous, depending on positions and distances among the chains jointed in proximity. Under heating, Iα was not converted into Iß but was simply destroyed. The jointed structure implies a "working and resting rhythm" in the biosynthesis of cellulose.

Graphene nanosheets homogeneously incorporated in polyurethane sponge for the elimination of water-soluble organic dyes.

Highly dispersed graphene nanosheets (GNS) are directly integrated into polyurethane sponge for the very first time. Individual GNS with an average thickness of 5 nm were uniformly encapsulated in polyurethane sponge (PUF). Highly durable, flexible, hydrophilic GNS/PUF demonstrated excellent organic dye absorption properties. For a detailed study, we selected typical water-soluble organic dyes such as methylene blue (MB), ethidium bromide (EtBr), eosin Y (EY). The adsorption behavior follows the Langmuir isotherm model indicating strong monolayer chemisorption. Adsorption capacity (µmol/g) of GNS while using in GNS/PUF is 586.8 (MB), 843.1 (EtBr), and 813.3 (EY). Thermodynamic study on the adsorption with three organic dyes using GNS/PUF revealed that the process was spontaneous and exothermic in nature. Additionally, the rate of adsorption is higher and follow the pseudo-second-order kinetic model. The detailed pH-dependent study showed that cationic dyes' adsorption increases with an increase in pH, and anionic dyes follow the opposite trend. The overall results show that the new adsorbent has highly suitable for practical application.

Uranium In Situ Electrolytic Deposition with a Reusable Functional Graphene-Foam Electrode.

Nuclear fission produces 400 GWe which represents 11% of the global electricity output. Uranium is the essential element as both fission fuel and radioactive waste. Therefore, the recovery of uranium is of great importance. Here, an in situ electrolytic deposition method to extract uranium from aqueous solution is reported. A functionalized reduced graphene oxide foam (3D-FrGOF) is used as the working electrode, which acts as both a hydrogen evolution reaction catalyst and a uranium deposition substrate. The specific electrolytic deposition capacity for U(VI) ions with the 3D-FrGOF is 4560 mg g-1 without reaching saturation, and the Coulombic efficiency can reach 54%. Moreover, reduction of the uranium concentration in spiked seawater from 3 ppm to 19.9 ppb is achieved, which is lower than the US Environmental Protection Agency uranium limits for drinking water (30 ppb). Furthermore, the collection electrode can be efficiently regenerated and recycled at least nine times without much efficiency fading, by ejecting into 2000 ppm concentrated uranium solution in a second bath with reverse voltage bias. All these findings open new opportunities in using free-standing 3D-FrGOF electrode as an advanced separation technique for water treatment.

Monolayered Platinum Nanoparticles as Efficient Electrocatalysts for the Mass Production of Electrolyzed Hydrogen Water.

High-performance/low-cost platinum (Pt)-based electrocatalysts have been established by top-coating both sides of a titanium plate with Pt nanoparticles. The average diameter of the Pt nanoparticles used in this study is approximately 100 nm. Three types of Pt top-coated Pt/Ti electrocatalysts, each having different top-coated Pt layer thicknesses, are prepared. Type I is a monolayered Pt top-coated type, in which the thickness of the top-coated Pt layer is approximately 100 nm; Type II is a few-layered type with a top-coated Pt layer thickness of approximately 200 nm, and Type III is a multilayered type with a top-coated Pt layer thickness of approximately 750 nm. The mass loading of Pt is 0.0215 mg cm-2 for Type I, 0.043 mg cm-2 for Type II, and 0.161 mg cm-2 for Type III. The electrocatalytic activities of each type of Pt/Ti electrocatalyst are evaluated through the electrolysis of acidic water and tap water. Type I gives the highest electrocatalytic efficiencies, which are comparable or even better than the electrocatalytic efficiencies of the state-of-the-art commercially available Pt/C electrode and other metal-/carbon-based HER catalysts. For example, in the case of the electrolysis of acidic water at an overpotential of 0.15 V, Type I shows a Tafel slope of 29 mV dec-1 and a current density of 27.5 mA cm-2. Even in the case of the electrolysis of tap water, Type I gives an HER Faradaic efficiency of 92%. A model of water (H2O), hydronium ions (H3O+), and hydroxyl ions (OH-) properly adsorbing on the Pt (111) facet is proposed to explain the electrocatalytic mechanism. New insights into the distinguishing properties of the resultant electrolyzed hydrogen water (EHW), namely, the healthy beneficial effects of EHW, are also described, and a new concept of storing and carrying reductive hydrogen (H*) by free Pt nanoparticles is proposed.

Stabilization of Prussian blue using copper sulfate for eliminating radioactive cesium from a high pH solution and seawater.

Prussian blue (PB), an adsorbent for the selective elimination of radioactive cesium from water, is highly versatile due to its unique crystal structure. However, PB crystals quickly decompose in an alkaline solution, generating hazardous cyanide contamination. In this research, the alkaline susceptibility of PB was remedied by incorporating copper sulfate as a protector. A stability assessment was conducted at several environmental conditions, such as high pH and temperatures from 10 °C to 50 °C, in seawater, artificial seawater, and river water. The crystalline and chemical stability of PB in the new class of composite was extremely high, even at a pH value of 11.2, as confirmed using XRD and total cyanide analysis. A comprehensive mechanism study revealed that, at high pH, the copper ions that cover the PB react with hydroxide ions to form copper hydroxide and shielding inner crystals. To decontaminate radioactive cesium, the first step was to immobilize nano PB on a cellulose nanofiber, followed by copper sulfate stabilization. Then, a spongiform adsorbent was made using polyurethane as the precursor. The new stabilized PB showed promising adsorption efficiency. Thus, this research will open a new range of applications for all existing and emerging PB-based adsorbents.

Selective elimination of lead(II) ions by alginate/polyurethane composite foams.

A new type of adsorbent which is capable of selectively adsorbing lead(II) ions (Pb(2+)) was developed. The adsorbent was generated by reaction of sodium alginate with NB-9000B, a polyisocyanate type of prepolymer of polyurethane. The adsorbent was a hydrophilic and flexible alginate/polyurethane composite foam (ALG/PUCF) with the alginate chemically immobilized in the cell walls of the foam. Acid-base titration was used to quantify the concentration of carboxyl groups, which are present on the alginate molecules of the ALG/PUCF, functioning as the essential sites for binding Pb(2+). For the optimized ALG/PUCF, the carboxyl was found to be 38.2+/-1.2mumol/g of dry weight. The capacity for adsorbing Pb(2+) ions in 1.0g of dry weight of the optimized ALG/PUCF was found to be 16.0+/-2.1mumol, indicating that ion exchange was the essential mechanism for adsorbing Pb(2+) ions. The adsorption capacity was found to be highly sensitive to the pH of the sample solution; lower pH (<3) significantly decreased the adsorption. Competing ions such as Mg(2+), Ca(2+), and Cd(2+) also caused a decrease in selectivity and capacity for Pb(2+) adsorption, although the effect was less pronounced than the effect of pH. The ALG/PUCF is highly stable, flexible and easy to use. ALG/PUCF is also reusable after regeneration with ethylenediamine-N,N,N',N'-tetraacetic acid, disodium salt (EDTA-2Na). Due to these features, this adsorbent may be highly useful for elimination of Pb(2+) ions from contaminated water.

Electrochemically reduced water exerts superior reactive oxygen species scavenging activity in HT1080 cells than the equivalent level of hydrogen-dissolved water.

Electrochemically reduced water (ERW) is produced near a cathode during electrolysis and exhibits an alkaline pH, contains richly dissolved hydrogen, and contains a small amount of platinum nanoparticles. ERW has reactive oxygen species (ROS)-scavenging activity and recent studies demonstrated that hydrogen-dissolved water exhibits ROS-scavenging activity. Thus, the antioxidative capacity of ERW is postulated to be dependent on the presence of hydrogen levels; however, there is no report verifying the role of dissolved hydrogen in ERW. In this report, we clarify whether the responsive factor for antioxidative activity in ERW is dissolved hydrogen. The intracellular ROS scavenging activity of ERW and hydrogen-dissolved water was tested by both fluorescent stain method and immuno spin trapping assay. We confirm that ERW possessed electrolysis intensity-dependent intracellular ROS-scavenging activity, and ERW exerts significantly superior ROS-scavenging activity in HT1080 cells than the equivalent level of hydrogen-dissolved water. ERW retained its ROS-scavenging activity after removal of dissolved hydrogen, but lost its activity when autoclaved. An oxygen radical absorbance capacity assay, the 2,2-diphenyl-1-picrylhydrazyl assay and chemiluminescence assay could not detect radical-scavenging activity in both ERW and hydrogen-dissolved water. These results indicate that ERW contains electrolysis-dependent hydrogen and an additional antioxidative factor predicted to be platinum nanoparticles.

Corrigendum: Nitrogen-doped porous carbon monoliths from polyacrylonitrile (PAN) and carbon nanotubes as electrodes for supercapacitors.

This corrects the article DOI: 10.1038/srep40259.

Dose effects of beta-tricalcium phosphate nanoparticles on biocompatibility and bone conductive ability of three-dimensional collagen scaffolds.

Three-dimensional collagen scaffolds coated with beta-tricalcium phosphate (ß-TCP) nanoparticles reportedly exhibit good bioactivity and biodegradability. Dose effects of ß-TCP nanoparticles on biocompatibility and bone forming ability were then examined. Collagen scaffold was applied with 1, 5, 10, and 25 wt% ß-TCP nanoparticle dispersion and designated TCP1, TCP5, TCP10, and TCP25, respectively. Compressive strength, calcium ion release and enzyme resistance of scaffolds with ß-TCP nanoparticles applied increased with ß-TCP dose. TCP5 showed excellent cell-ingrowth behavior in rat subcutaneous tissue. When TCP10 was applied, osteoblastic cell proliferation and rat cranial bone augmentation were greater than for any other scaffold. The bone area of TCP10 was 7.7-fold greater than that of non-treated scaffold. In contrast, TCP25 consistently exhibited adverse biological effects. These results suggest that the application dose of ß-TCP nanoparticles affects the scaffold bioproperties; consequently, the bone conductive ability of TCP10 was remarkable.

Nitrogen-doped porous carbon monoliths from polyacrylonitrile (PAN) and carbon nanotubes as electrodes for supercapacitors.

Nitrogen-doped porous activated carbon monoliths (NDP-ACMs) have long been the most desirable materials for supercapacitors. Unique to the conventional template based Lewis acid/base activation methods, herein, we report on a simple yet practicable novel approach to production of the three-dimensional NDP-ACMs (3D-NDP-ACMs). Polyacrylonitrile (PAN) contained carbon nanotubes (CNTs), being pre-dispersed into a tubular level of dispersions, were used as the starting material and the 3D-NDP-ACMs were obtained via a template-free process. First, a continuous mesoporous PAN/CNT based 3D monolith was established by using a template-free temperature-induced phase separation (TTPS). Second, a nitrogen-doped 3D-ACM with a surface area of 613.8 m2/g and a pore volume 0.366 cm3/g was obtained. A typical supercapacitor with our 3D-NDP-ACMs as the functioning electrodes gave a specific capacitance stabilized at 216 F/g even after 3000 cycles, demonstrating the advantageous performance of the PAN/CNT based 3D-NDP-ACMs.

Voltammetric behavior and determination of 17 beta-estradiol at multi-wall carbon nanotube-Nafion modified glassy carbon electrode.

For the purpose of low cost and sensitive electrochemical detection of 17 beta-estradiol (E2), a multi-wall carbon nanotube (MWNT)-Nafion modified electrode was fabricated. The MWNT modified electrode shows enhancement for the anodic peak current of E2 compared with the value obtained using a bare electrode. The anodic peak current measured by square wave voltammetry after 5 min open-circuit accumulation was proportional to the concentration of E2 over the range of 2.5 x 10(-7) to 10 10(-6) M, and a detection limit of 1 x 10(-8) M was obtained.

Cellulose nanofiber backboned Prussian blue nanoparticles as powerful adsorbents for the selective elimination of radioactive cesium.

On 11 March 2011, the day of the unforgettable disaster of the 9 magnitude Tohoku earthquake and quickly followed by the devastating Tsunami, a damageable amount of radionuclides had dispersed from the Fukushima Daiichi's damaged nuclear reactors. Decontamination of the dispersed radionuclides from seawater and soil, due to the huge amounts of coexisting ions with competitive functionalities, has been the topmost difficulty. Ferric hexacyanoferrate, also known as Prussian blue (PB), has been the most powerful material for selectively trapping the radioactive cesium ions; its high tendency to form stable colloids in water, however, has made PB to be impossible for the open-field radioactive cesium decontamination applications. A nano/nano combinatorial approach, as is described in this study, has provided an ultimate solution to this intrinsic colloid formation difficulty of PB. Cellulose nanofibers (CNF) were used to immobilize PB via the creation of CNF-backboned PB. The CNF-backboned PB (CNF/PB) was found to be highly tolerant to water and moreover, it gave a 139 mg/g capability and a million (106) order of magnitude distribution coefficient (Kd) for absorbing of the radioactive cesium ion. Field studies on soil and seawater decontaminations in Fukushima gave satisfactory results, demonstrating high capabilities of CNF/PB for practical applications.

Removal of organic compounds by alginate gel beads with entrapped activated carbon.

The adsorption of alginate gel (AG) beads and AG with activated carbon entrapped (AG-AC) beads prepared using different types of metal ions were investigated by measuring the removal of several organic compounds with different charges and size. AG-AC beads prepared in a CaCl2 solution adsorbed strongly positively charged compounds as well as electrically neutral and low molecular weight compounds such as p-chlorophenol. However, a high molecular weight humic acid was not adsorbed by AG-AC. The AG-AC selectively adsorbed p-chlorophenol from a humic acid solution. The adsorption capacity obtained from the adsorption isotherm of AC entrapped in AG was compared with that of AC. The AG-AC beads prepared in a solution of FeCl3 were able to specifically adsorb negatively charged gallic acid. Thus, entrapping AC into AG resulted in the selective adsorption.

DNA/Ag Nanoparticles as Antibacterial Agents against Gram-Negative Bacteria.

Silver (Ag) nanoparticles were produced using DNA extracted from salmon milt as templates. Particles spherical in shape with an average diameter smaller than 10 nm were obtained. The nanoparticles consisted of Ag as the core with an outermost thin layer of DNA. The DNA/Ag hybrid nanoparticles were immobilized over the surface of cotton based fabrics and their antibacterial efficiency was evaluated using E. coli as the typical Gram-negative bacteria. The antibacterial experiments were performed according to the Antibacterial Standard of Japanese Association for the Functional Evaluation of Textiles. The fabrics modified with DNA/Ag nanoparticles showed a high enough inhibitory and killing efficiency against E. coli at a concentration of Ag ≥ 10 ppm.

Three-dimensional Nitrogen-Doped Graphene Supported Molybdenum Disulfide Nanoparticles as an Advanced Catalyst for Hydrogen Evolution Reaction.

An efficient three-dimensional (3D) hybrid material of nitrogen-doped graphene sheets (N-RGO) supporting molybdenum disulfide (MoS(2)) nanoparticles with high-performance electrocatalytic activity for hydrogen evolution reaction (HER) is fabricated by using a facile hydrothermal route. Comprehensive microscopic and spectroscopic characterizations confirm the resulting hybrid material possesses a 3D crumpled few-layered graphene network structure decorated with MoS(2) nanoparticles. Electrochemical characterization analysis reveals that the resulting hybrid material exhibits efficient electrocatalytic activity toward HER under acidic conditions with a low onset potential of 112 mV and a small Tafel slope of 44 mV per decade. The enhanced mechanism of electrocatalytic activity has been investigated in detail by controlling the elemental composition, electrical conductance and surface morphology of the 3D hybrid as well as Density Functional Theory (DFT) calculations. This demonstrates that the abundance of exposed active sulfur edge sites in the MoS(2) and nitrogen active functional moieties in N-RGO are synergistically responsible for the catalytic activity, whilst the distinguished and coherent interface in MoS(2)/N-RGO facilitates the electron transfer during electrocatalysis. Our study gives insights into the physical/chemical mechanism of enhanced HER performance in MoS(2)/N-RGO hybrids and illustrates how to design and construct a 3D hybrid to maximize the catalytic efficiency.