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Highlights: [•] Electrical percolation is based on electrical connectivity in randomly oriented systems of discrete elements. [•] Biological semiconductor is a multi-layer 3-D carbon nanotube-antibody network with a biological ligand. [•] Molecular interactions disrupt the network continuity causing increased resistance of the network. [•] We demonstrated real time continuous detection of staphylococcal enterotoxin B at concentrations of 1ng/ml. [•] This new direct measurement biosensor has potential for multi-target real time detection. [ABSTRACT FROM AUTHOR]

Let q be a power of an odd prime, and be the trace mapping. A mapping is called planar (or perfect nonlinear) on if for any non-zero , the difference mapping is a permutation where for , . Kyureghyan and Özbudak (2012) [8] considered the planarity of mappings on for and proved that there is no planar for . For the case and , they raised three conjectures. In this paper we prove the third conjecture which says that there is no planar for , by using Kloosterman sums. Our proof also works for case , so we present a new proof of the Kyureghyan–Özbudak result. For case , we present an elementary proof of the first conjecture which says that there is no planar for . [ABSTRACT FROM AUTHOR]

Transition metal nitrides (TMN) have many desirable characteristics such as high hardness and good thermal stability under reducing conditions. This work reports an initial survey of the chemical stability of mesoporous TMNs (TM=Nb, V, Cr and Ti) in water at 80°C at neutral, acidic and alkaline pH. The mesoporous TMNs had specific surface areas of 25–60m2/g with average pore sizes ranging from 10 to 50nm. The high surface areas of these materials enhance the rate of corrosion per unit mass over that of a bulk material, making detection of corrosion much easier. The products were characterized by Rietveld refinement of powder X-ray diffraction (PXRD) patterns and by scanning electron microscopy (SEM). Several nitrides have corrosion rates that are, within error, not distinguishable from zero (±1Å/day). Of the nitrides examined, CrN appears to be the most corrosion resistant under acidic conditions. None of the nitrides studied are corrosion resistant under alkaline conditions. [ABSTRACT FROM AUTHOR]

Abstract: We recently reported a simple route to prepare mesoporous, conducting nitrides from Zn containing ternary transition metal oxides. Those materials result from the condensation of atomic scale voids created by the loss of Zn by evaporation, the replacement of 3 oxygen anions by 2 nitrogen anions, and in most cases the loss of oxygen to form water on the reduction of the transition metal. In this report, we present a different route to prepare mesoporous VN from K containing vanadium oxides. In this case, ammonolysis results in a multiphase solid product that contains VN, and other water soluble compounds such as KOH or KNH2. On removing the K containing products by washing with degassed water, only mesoporous VN remains. VN materials with different pore sizes (10nm–20nm) were synthesized at 600°C by varying the reaction time, while larger pores are obtained at higher temperatures (50nm at 800°C). [Copyright &y& Elsevier]

Abstract: An automated point-of-care (POC) immunodetection system for immunological detection of staphylococcal enterotoxin B (SEB) was designed, fabricated, and tested. The system combines several elements: (i) enzyme-linked immunosorbent assay–lab-on-a-chip (ELISA–LOC) with fluidics, (ii) a charge-coupled device (CCD) camera detector, (iii) pumps and valves for fluid delivery to the ELISA–LOC, (iv) a computer interface board, and (v) a computer for controlling the fluidics, logging, and data analysis of the CCD data. The ELISA–LOC integrates a simple microfluidic system into a miniature 96-well sample plate, allowing the user to carry out immunological assays without a laboratory. The analyte is measured in a sandwich ELISA assay format combined with a sensitive electrochemiluminescence (ECL) detection method. Using the POC system, SEB, a major foodborne toxin, was detected at concentrations as low as 0.1ng/ml. This is similar to the reported sensitivity of conventional ELISA. The open platform with simple modular fluid delivery automation design described here is interchangeable between detection systems, and because of its versatility it can also be used to automate many other LOC systems, simplifying LOC development. This new POC system is useful for carrying out various immunological and other complex medical assays without a laboratory and can easily be adapted for high-throughput biological screening in remote and resource-poor areas. [Copyright &y& Elsevier]

Abstract: A label-free immunosensor for the sensitive detection of human immunoglobulin G (IgG) was prepared based on gold nanoparticle–silver enhancement detection with a simple charge-coupled device (CCD) detector. The gold nanoparticles, which were used as nuclei for the deposit of metallic silver and also for the adsorption of antibodies, were immobilized into wells of a 9-well chip. With the addition of silver enhancement buffer, metallic silver will deposit onto gold nanoparticles, causing darkness that can be optically measured by the CCD camera and quantified using ImageJ software. When antibody was immobilized onto the gold nanoparticles and antigen was captured, the formed immunocomplex resulted in a decrease of the darkness and the intensity of the darkness was in line with IgG concentrations from 0.05 to 10ng/ml. The CCD detector is simple and portable, and the reported method has many desirable merits such as sensitivity and accuracy, making it a promising technique for protein detection. [Copyright &y& Elsevier]

Abstract: Conducting polymer film was prepared by electrochemical polymerization of aniline. Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. By using the layer-by-layer method, homogeneous and stable MWNTs and polyaniline (PANI) multilayer films were alternately assembled on glassy carbon (GC) electrodes. Conducting polymer of PANI had three main functions: (i) excellent antiinterference ability, (ii) protection ability in favor of increasing the amount of the MWNTs immobilized on GC electrodes, and (iii) superior transducing ability. The protection effect of PANI film and the electrostatic interaction between positively charged PANI and negatively charged MWNTs both attributed to immobilizing abundant MWNTs stably, thereby enhancing the catalytic activity. The layer-by-layer assembled MWNTs and PANI-modified GC electrodes offered a significant decrease in the overvoltage for the H2O2 and were shown to be excellent amperometric sensors for H2O2 from +0.2V over a wide range of concentrations. As an application example, by linking choline oxidase (CHOD), an amplified biosensor toward choline was prepared. The choline biosensor exhibited a linear response range of 1×10−6 to 2×10−3 M with a correlation coefficient of 0.997, and the response time and detection limit (S/N =3) were determined to be 3s and 0.3μM, respectively. The antiinterference biosensor displays a rapid response and an expanded linear response range as well as excellent reproducibility and stability. [Copyright &y& Elsevier]

An amperometric enzyme biosensor for the determination of choline utilizing two enzymes, choline oxidase (CHOD) and horseradish peroxidase (HRP), is described. The biosensor consisted of CHOD cross-linked onto a HRP-immobilized carbon paste electrode. The biosensor was prepared by in situ electropolymerization of poly(thionine) within a carbon paste containing the enzyme HRP and thionine monomer and then CHOD was immobilized by using chitosan film through cross-linking with glutaraldehyde. The in situ electrogenerated poly(thionine) displays excellent electron transform efficiency between the enzyme HRP and the electrode surface, and the polymer enables improvement in enzyme immobilization within the paste. Several parameters such as the amount of thionine and enzyme, the applied potential, the pH, etc. have been studied. Amperometric detection of choline was realized at an applied potential of −0.2V vs saturated calomel electrode in 1/15M phosphate buffer solution (pH 7.4) with a linear response range between 5.0×10−6 and 6.0×10−4M choline and a response time of 15s. When applied to the analysis of phosphatidylcholine in serum samples, a 0.997 correlation was obtained between the biosensor results and those obtained by a hospital method. [Copyright &y& Elsevier]

Graphical abstract Additional iron doping of N-doped graphene-like carbon sheets results in the formation of highly efficient Fe, N-codoped carbon sheets towards the electrocatalytic oxygen reduction, which also shows better long-term stability and resistance to methanol crossover than commercial Pt/C. Abstract Rational design and synthesis of Fe-N-codoped carbon materials are promising for replacing commercial Pt/C for oxygen reduction reaction (ORR). Herein, we develop a simple two-step pyrolysis approach to synthesize highly active Fe-N-codoped graphene-like carbon sheets (FeNGC) with active Fe-N-based species for ORR. In this strategy, two-dimensional nitrogen-doped graphene-like carbon sheets (NGC) with a high N-doping level (8.1 at%) and abundant mesoporosity (3.8 nm) are firstly synthesized by co-pyrolysis of biomass carbon source and dicyandiamide, in which dicyandiamide simultaneously serves as a trifunctional role of in situ reaction template, nitrogen source and porogen. Secondly, FeNGCs are prepared by additional iron doping of NGC at high temperatures, in which sheet-like structure is in favor of increased accessibility of N-functional groups to more Fe atoms, thus giving rise to formation of high-density Fe-N-based active sites. The optimized catalyst synthesized at 950 °C (FeNGC-950) demonstrates significantly increased ORR activity with a dominant 4e− reduction process compared to pure NGC in alkaline and acidic solutions, which evidently shows the comparable activity to Pt/C due to the synergy of simultaneously optimized structures and multi-active sites. Moreover, FeNGC-950 has better long-term stability and methanol tolerance than Pt/C both in alkaline and acidic electrolytes. The present strategy paves a new venue to design and prepare various metal-doped carbon materials with great potentials in energy applications. [ABSTRACT FROM AUTHOR]

In this paper, a series of nitrogen-doped mesoporous carbons (NMCs) with three-dimensional (3D) interconnected mesopores have been prepared using flour as carbon source, dicyanamide as nitrogen source and colloidal silica as hard template. The optimized material (NMC-4) prepared with the colloidal silica/flour mass ratio of 4 has a high nitrogen doping level of 5.69 at.% and large specific surface area of 995 m 2  g −1 as well as 3D interconnected mesopores (12.9 nm). As the oxygen reduction reaction (ORR) electrocatalyst among various NMCs, NMC-4 exhibits the superior performance and much better stability and methanol crossover with a four-electron dominant reaction pathway compared to commercial 20 wt% Pt/C. Furthermore, as a supercapacitor (SC) electrode material, NMC-4 exhibits a high specific capacitance of 178.5 F g −1 at a current density of 0.5 A g −1 and long cycle life (94.5% capacity retention after 5000 cycles). It also shows a good rate capacity as 76.1% of original specific capacitance remains when the current density increases from 0.5 to 20 A g −1 . The high-performance of NMCs results from the synergetic effects of 3D interconnected mesopores, large surface area, and high N-doping level, enabling fast mass transport and electron transfer during the electrochemical process. This work provides a facile and efficient strategy to heteroatom-doped carbons from extensively available biomass, showing great potentials in electrocatalysis, energy storage, and other applications. [ABSTRACT FROM AUTHOR]