Highly sensitive and selective solid-contact calcium sensor based on Schiff base of benzil with 3-aminosalycilic acid covalently attached to polyacrylic acid amide for health care

Solid-state potentiometric calcium sensors based on newly synthesized Schiff’s base of 3-aminosalycilic acid with benzil [2-hydroxy-3-(2-oxo-1,2-diphenylethylidene)amino) benzoic acid] ionophore I and with isatin [2-hydroxy-3-(2-oxoindolin-3-ylidene amino)benzoic acid] ionophore II ionophores and their covalently attached to polyacrylamide ionophores III and IV, respectively, were developed. The all-solid-state sensors were constructed by the application of a thin film of polymeric membrane cocktail onto gold electrodes that were pre-coated with the conducting polymer poly (3,4-ethylenedioxy-thiophen) as an ion and electron transducer. More than 40 sensors with membranes containing plasticized PVC or poly(butyl methacrylate-co-dodecyl methacrylate as a plasticizer-free membrane matrix were investigated. The constructed sensors contained various amounts of the different ionophores with and without anionic lipophilic additive. The sensor containing 10% of ionophore III and 3% tetra (p-chlorophenyl) borate in acrylate copolymer exhibited a stable potentiometric response over a wide pH range of 4–9. It possessed a linear concentration range of 6 10^?10 to 1 10^?2 mol L^?1 with a Nernstian slope of 28.5 mV/decade and a limit of detection (LOD) of 2 10^?10 mol L^?1. It exhibited a good selectivity for calcium to other cations. The selectivity coefficients towards different mono-, di- and trivalent cations were determined with the fixed interference method (FIM) and separate solution method (SSM). The sensor’s life time is more than 3 months, without significant deterioration in the slope. The proposed sensors were utilized for the determination of calcium concentration in serum. The results were compared with those obtained from routine clinical laboratory electrolyte analyser. The results reveal that the all-solid-state calcium sensor is promising for the point of care testing.     

Phylogenetic Analysis and Biological Evaluation of Marine Endophytic Fungi Derived from Red Sea Sponge <Emphasis Type="Italic">Hyrtios erectus</Emphasis>

Forty-four endophytic fungal isolates obtained from marine sponge, Hyrtios erectus, were evaluated and screened for their hydrolase activities. Most of the isolates were found to be prolific producers of hydrolytic enzymes. Only 11 isolates exhibited maximum cellular contents of lipids, rhamnolipids, and protein in the fungal isolates under the isolation numbers MERVA5, MERVA22, MERVA25, MERVA29, MERVA32, MERVA34, MERV36, MERVA39, MERVA42, MERVA43, and MERVA44. These isolate extracts exhibit the highest reducing activities against carbohydrate-metabolizing enzymes including α-amylase, α-glucosidase, β-glucosidase, β-glucuronidase, and tyrosinase. Consequently, based on morphological and cultural criteria, as well as sequence information and phylogenetic analysis, these isolates could be identified and designated as Penicillium brevicombactum MERVA5, Arthrinium arundinis MERVA22, Diaporthe rudis MERVA25, Aspergillus versicolor MERVA29, Auxarthron alboluteum MERVA32, Dothiorella sarmentorum MERVA34, Lophiostoma sp. MERVA36, Fusarium oxysporum MERVA39, Penicillium chrysogenum MERVA42, Penicillium polonicum MERVA43, and Trichoderma harzianum MERVA44. The endophytic fungal species, D. rudis MERVA25, P. polonicum MERVA43, Lophiostoma sp. MERVA36, A. alboluteum MERVA32, T. harzianum MERVA44, F. oxysporum MERVA39, A. versicolor MERVA29, and P. chrysogenum MERVA42 extracts, showed significant hepatitis C virus (HCV) inhibition. Moreover, D. sarmentorum MERVA34, P. polonicum MERVA43, and T. harzianum MERVA44 extracts have the highest antitumor activity against human hepatocellular carcinoma cells (HepG2).     

Preparation of a novel stir bar coating based on montmorillonite doped polypyrrole/nylon-6 nanocomposite for sorptive extraction of organophosphorous pesticides in aqueous samples

In the present work, a novel nanocomposite (NC) was prepared by reinforcing montmorillonite (MMT) into polypyrrole-nylon-6 (PPy-N6) hybrid through in situ oxidative polymerisation of PPy in the MMT-N6 mixture. The prepared novel NC was deposited as a thin layer coating on the stir bar substrate by solvent exchange method. Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy were applied to characterise the prepared NCs. The prepared stir bar based on MMT/PPy/N6 NC was applied for sorptive extraction of some organophosphorous pesticides (OPPs) in river water samples with detection by gas chromatography-mass spectrometry (GC-MS). The effect of MMT doping level in the NC and also the effect of PPy hybridation with N6 on the coating extraction capability were studied. Central composite design was used to optimise and study the effects of influencing factors on the stir bar sorptive extraction efficiency such as salt content, pH, extraction time, desorption time, desorption solvent and its volume. The method optimisation step was performed using gas chromatography-flame ionisation detector, while the method validation was conducted using GC-MS. Limits of detection of the developed method are in the range of 0.05–0.3 μg L^?1 and the linear dynamic ranges are in the range of 0.3–1000 and 1–1000 μg L^?1, respectively. The intra-day precision (RSD %) of developed method with four replicates varied between 5.4 and 8.2% for distilled water spiked at 100 μg L^?1. The applicability of the developed method was examined by extraction and determination of OPP compounds in river water samples, indicating the relative recoveries in the range of 80.3–95.3%.     

Voltammetric determination of 4-nitrophenol using a glassy carbon electrode modified with a gold-ZnO-SiO<Subscript>2</Subscript> nanostructure

A nanostructured material of the type Au-ZnO-SiO₂ is described that consists of ZnO and gold nanoparticles (NPs) dispersed into a silica matrix and used to construct a voltammetric sensor for 4-nitrophenol. The AuNPs and ZnO NPs are anchored onto the silica network which warrants the nanostructures to be stable in various environments. It also facilitates the electron transfer between the electrolyte and the glassy carbon electrode (GCE). The properties of the nanostructure as a modifier for the GCE were investigated by energy dispersive spectrometry, X-ray diffraction spectroscopy, and transmission electron microscopy. It is shown that the nanostructure increases the surface area. Hence, the cathodic and anodic current in differential pulse voltammetry of 4-nitrophenol are considerably enhanced in comparison to a bare GCE. Under optimum conditions, the currents for oxidation and reduction are proportional to the concentration of 4-nitrophenol in the 0.05–3.5 μM and 0.01–1.2 μM concentration ranges, with 13.7 and 2.8 nM detection limits, respectively. The sensor has excellent sensitivity, fast response, long-term stability, and good reproducibility. It is perceived to be a valuable tool for monitoring 4-nitrophenol in real water samples.

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Graphical abstract Schematic of voltammetric sensor for 4-nitrophenol. It is based on GCE modified with gold-ZnO-SiO₂ nanostructure. It exhibited the improvement in performance for both oxidation and reduction peaks in terms of linearity, concentration range, detection limit, and sensitivity.

     

Citronellal cyclisation over heteropoly acid supported on modified montmorillonite catalyst: effects of acidity and pore structure on catalytic activity

Citronellal cyclisation to isopulegol is an important intermediate step in the production of menthol. Several heteropoly acids (PTA) supported on modified montmorillonite (MM) catalysts were synthesized and then tested in cyclisation reactions. The prepared samples were characterized by XRD, ICP-OES, FTIR, N₂ sorption, NH₃-TPD, pyridine adsorption, amine titration and FE-SEM techniques. Effects of post-treatment were studied on montmorillonite pore structure, acidity and catalytic activity. The catalytic activity and isopulegol selectivity improved with acid-treatment and PTA loading. The amount of Lewis acidity of montmorillonite was enhanced with acid-treatment and PTA impregnation. In cyclisation, highest catalytic activity (31.87 mmol cat g^?1 min^?1) was achieved with 96% isopulegol yield in the use of 20% PTA-MM catalyst. The highest catalytic activity and selectivity were obtained in the presence of higher acidity and strong Lewis acidic sites, whereas effects of pore structure blockage seemed minor. The catalytic activity further decreased with the loss of active acidic sites (L and B) due to PTA decomposition with calcination at a higher temperature.     

Periodic orbits in magnetic fields and Ricci curvature of Lagrangian systems

A Lagrangian system describing a motion of a charged particle on a Riemannian manifold is studied. For this flow an analog of a Ricci curvature is introduced, and for Ricci positively curved flows the existence of periodic orbits is proved.

     

Current transport mechanism of Mg/Au ohmic contacts to lightly doped n-type β-Ga2O3

The carrier transport mechanism of Mg/Au ohmic contact for lightly doped β-Ga_2O_3 is investigated. An excellent ohmic contact has been achieved when the sample was annealed at 400 °C and the specific contact resistance is 4.3 × 10-4 Ω·cm2. For the annealed sample, the temperature dependence of specific contact resistance is studied in the range from 300 to 375 K. The specific contact resistance is decreased from 4.3 × 10-4 to 1.59 × 10-4 Ω·cm2 with an increase of test temperature. As combination with the judge of E00, the basic mechanism of current transport is dominant by thermionic emission theory. The effective barrier height between Mg/Au and β-Ga_2O_3 is evaluated to be 0.1 eV for annealed sample by fitting experimental data with thermionic emission model.     

Pushing PbS/Metal‐Halide‐Perovskite Core/Epitaxial‐Ligand‐Shell Nanocrystal Photodetectors beyond 3 µm Wavelength

PbS nanocrystals have been proven to be highly suitable for photodetector fabrication by facile solution processing, and have been successfully tested as photosensitive material in imaging devices. So far, their spectral response has been blue‐shifted with respect to that of commercial bulk PbS detectors, due to quantum confinement in nanostructures smaller than the exciton Bohr radius. Here, a PbS nanocrystal synthesis approach is introduced, allowing to surpass this limit, and thus to push the cut‐off wavelength to the value of the bulk material. To avoid self‐absorbance from ligands within the spectral range of the photoconducting signal, an all inorganic metal‐halide‐perovskite is applied to form a semiconducting ligand shell. The photoconductors, which are provided from a single drop, do not only show a record in long wavelength operation for PbS nanocrystal detectors but also a room temperature detectivity > 10¹⁰ Jones, which is on par with that of commercial bulk PbS detectors. Combining these properties might find application in future low‐cost infrared imagers, which are currently still elusive due to their high prices.     

Silver‐Adapted Diffusive Memristor Based on Organic Nitrogen‐Doped Graphene Oxide Quantum Dots (N‐GOQDs) for Artificial Biosynapse Applications

Carbon‐based electronic devices are suitable candidates for bioinspired electronics due to their low cost, eco‐friendliness, mechanical flexibility, and compatibility with complementary metal‐oxide‐semiconductor technology. New types of materials such as graphene quantum dots (GQDs) have attracted attention in the search for new applications beyond solar cells and energy harvesting due to their superior properties such as elevated photoluminescence, high chemical inertness, and excellent biocompatibility. In this paper, a biocompatible/organic electronic synapse based on nitrogen‐doped graphene oxide quantum dots (N‐GOQDs) is reported, which exhibits threshold resistive switching via silver cation (Ag⁺) migration dynamics. In analogy to the calcium (Ca²⁺) ion dynamics of biological synapses, important biological synapse functions such as short‐term potentiation (STP), paired‐pulse facilitation, and transition from STP to long‐term plasticity behaviors are replicated. Long‐term depression behavior is also evaluated and specific spike‐timing dependent plasticity is assessed. In addition, elaborated switching mechanism of biosimilar Ag⁺ migration dynamics provides the potential for using N‐GOQD‐based artificial synapse in future biocompatible neuromorphic systems.     

3D Graphene Network with Covalently Grafted Aniline Tetramer for Ultralong-Life Supercapacitors

The conducting polymer polyaniline (PANI) has been considered to be a promising pseudocapacitive electrode material for supercapacitors due to its high specific capacitance, low cost, and environmental friendliness. However, the poor cycling stability of PANI during the charge–discharge processes limits its widespread practical application. Herein, a facile synthetic method is demonstrated for covalently grafting an aniline tetramer (TANI), the basic building block of PANI, onto 3D graphene networks via perfluorophenylazide coupling chemistry to create a hybrid electrode material for ultralong-life supercapacitors. The design, which substitutes long-chain PANI with short-chain TANI and introduces covalent linkages between TANI and 3D graphene, greatly enhances the charge–discharge cycling stability of PANI-based supercapacitors. The electrode material, as well as the fabricated symmetric all-solid-state supercapacitors, exhibit extraordinary long cycle life (>85% capacitance retention after 30 000 charge–discharge cycles). The capacitance can be further boosted through fast and reversible redox reactions on the electrode surface using a redox-active electrolyte while maintaining outstanding cycling stability (82% capacitance retention after 100 000 cycles for a symmetric all-solid-state device). While conducting polymers are known to be limited by their poor cycling stability, this work provides an effective strategy to achieve enhanced cycle life for conducting polymer-based energy storage devices.