Mediatorless Hydrogen Peroxide Biosensor Based on Horseradish Peroxidase Immobilized on 4‐Carboxyphenyl Film Electrografted on Gold Electrode

A novel method to fabricate a third‐generation hydrogen peroxide biosensor was reported. The electrode was first derivatized by electrochemical reduction of in situ generated 4‐carboxyphenyl diazonium salt (4‐CPDS) in acidic aqueous solution yielded stable 4‐carboxyphenyl (4‐CP) layer. The horseradish peroxidase (HRP) enzyme was then covalently immobilized by amidation between NH₂ terminus of enzyme and COOH terminus of 4‐CP film making use of the carbodiimide chemistry. Electrodeposition conditions used to control electrode functionalization density and film electron transfer kinetics were assessed by chronoamperometry and electrochemical impedance spectroscopy. The immobilized HRP displayed excellent electrocatalytic activity towards the reduction of hydrogen peroxide (H₂O₂) without any mediators. The effect of various operational parameters was explored for optimum analytical performance. The reported biosensor exhibited fast amperometric response (within 5 s) to H₂O₂. The detection limit of the biosensor was 5 μM, and linear range was from 20 μM to 20 mM. Furthermore, the biosensor exhibited high sensitivity, good reproducibility, and long‐term stability.     

Characterization of self-assembled monolayers (SAMs) on silicon substrate comparative with polymer substrate for Escherichia coli O157:H7 detection

This article presents the characterization of two substrates, silicon and polymer coated with gold, that are functionalized by mixed self-assembled monolayers (SAMs) in order to efficiently immobilize the anti-Escherichia coli O157:H7 polyclonal purified antibody.A biosurface functionalized by SAMs (self-assembled monolayers) technique has been developed. Immobilization of goat anti-E. coli O157:H7 antibody was performed by covalently bonding of thiolate mixed self-assembled monolayers (SAMs) realized on two substrates: polymer coated with gold and silicon coated with gold. The F(ab′)₂ fragments of the antibodies have been used for eliminating nonspecific bindings between the Fc portions of antibodies and the Fc receptor on cells. The properties of the monolayers and the biofilm formatted with attached antibody molecules were analyzed at each step using infrared spectroscopy (FTIR-ATR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV). In our study the gold-coated silicon substrates approach yielded the best results.These experimental results revealed the necessity to investigate each stage of the immobilization process taking into account in the same time the factors that influence the chemistry of the surface and the further interactions as well and also provide a solid basis for further studies aiming at elaborating sensitive and specific immunosensor or a microarray for the detection of E. coli O157:H7.     

Thermal atomic vibrations in Cu-Ni alloys

Copper radiation has been used in an x-ray study of the temperature dependence of the effective characteristic x-ray temperature _p(T) for the alloys of the Cu-Ni system over the temperature range 293–1073 °K and in a determination of the concentration dependence of d ln_p/dT for the alloys. It is shown that _p(c) is additive. The concentration dependence of d ln_p/dT is linear. The agreement between the experimental results and data in the literature is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 75–80, September, 1970.     

Electroactivity of Superoxide Anion in Aqueous Phosphate Buffers Analyzed with Platinized Microelectrodes

The reactivity of platinized ultramicroelectrodes (Pt-black UMEs) towards superoxide anion O₂^.−, an unstable Reactive Oxygen Species (ROS), and its relatives, H₂O₂ and O₂, was studied. Voltammetric studies in PBS demonstrate that Pt-black UMEs provide: i) a well-resolved reversible redox signature for O₂^.− detected in both alkaline and physiological buffers (pH 12 and 7.4); ii) irreversible oxidation and reduction waves for H₂O₂ at pH 7.4. The oxygen reduction reaction (ORR) at Pt-black surfaces solely yields H₂O₂ (2 electrons/2 H⁺) at physiological pH. Consequently, Pt-black UMEs allow to sense different ROS including superoxide anion for future biomedical or physico-chemical investigations.     

Determination of Antioxidant Capacity by Using Xanthine Oxidase Bioreactor Coupled with Flow‐through H2O2 Amperometric Biosensor

A new flow system for antioxidant capacity (AOC) estimation, consisting of a bioreactor, containing immobilized xanthine oxidase (XOD), coupled with a H₂O₂ amperometric biosensor, based on Os‐wired horseradish peroxidase, was developed. The H₂O₂, resulting from the enzymatic reaction between xanthine (XA) and XOD, was amperometrically monitored at ?0.1 V vs. Ag/AgCl/KCl_sat, in order to avoid the electrochemical interferences. Two protocols were used to perform the AOC evaluation: “steady‐state”, when the antioxidant (AOX) was injected in the XA flow, and “transient state”, when XA and AOX were simultaneously injected in the carrier flow. The AOC of some commercial beverages were evaluated and compared with those obtained with 2,2‐diphenyl‐1‐picrylhydrazyl radical and Folin–Ciocalteu methods.     

Preparation and characterization of PbTiO3–epoxy resin compositionally graded thick films

The preparation and properties of compositionally graded PbTiO₃ (PT)–epoxy resin (EPR) composite thick films are reported in this study. Various graded specimens were prepared using gravity casting method by embedding PT powders into the EPR matrix. The existence of a graded structure with two distinct phases, a good intermixing, some air pores, and different morphologies, was confirmed by scanning electron microscopy micrographs. The dielectric constants of these composites have values in the range 5–12 at the frequency of ～10⁴?Hz and about 3–13 at ～5?×?10^8?Hz. The composites with permittivity gradient act as a natural impedance match system in the frequency range 2–4?GHz, resulting in very low reflections. Therefore, the compositionally graded PT–EPR composite thick films are suitable as adapting impedance materials for microwave applications.     

The Effect of Sodium Total Substitution on the Quality Characteristics of Green Pickled Tomatoes (Solanum lycopersicum L.)

Green pickled tomatoes are a traditional fermented product in Romania. This study was focused on the effect of total substitution of NaCl with KCl and MgCl₂ on physicochemical and microbiological quality; bioactive compounds; and microstructural, textural, and sensorial properties of fresh and pickled green tomatoes during 28 days of fermentation. By the means of physicochemical composition, the NaCl addition induced the most stable characteristics for the pickles compared to the other two types of salts. The content of total flavonoids in green pickled tomatoes with NaCl (34.72 ± 0.43 mg CE/g DW) was significantly lower compared with the control sample (63.80 ± 0.55 mg CE/g DW). The total number of lactic acid bacteria (LAB) at the final stage of fermentation varied between 4.11 and 4.63 log CFU for all variants. The textural analysis revealed that the NaCl has the lowest influence on the textural parameters. Finally, the overall acceptance of green pickled tomatoes containing KCl and MgCl₂ was found to be proper to be consumed as a substitute for pickles with NaCl.     

Stimuli-Responsive Thiomorpholine Oxide-Derived Polymers with Tailored Hydrophilicity and Hemocompatible Properties

Thermo-responsive hydrophilic polymers, including those showing tuneable lower critical solution temperature (LCST), represent a continuous subject of exploration for a variety of applications, but particularly in nanomedicine. Since biological pH changes can inform the organism about the presence of disequilibrium or diseases, the development of dual LCST/pH-responsive hydrophilic polymers with biological potential is an attractive subject in polymer science. Here, we present a novel polymer featuring LCST/pH double responsiveness. The monomer ethylthiomorpholine oxide methacrylate (THOXMA) can be polymerised via the RAFT process to obtain well-defined polymers. Copolymers with hydroxyethyl methacrylate (HEMA) were prepared, which allowed the tuning of the LCST behaviour of the polymers. Both, the LCST behaviour and pH responsiveness of hydrophilic PTHOXMA were tested by following the evolution of particle size by dynamic light scattering (DLS). In weak and strong alkaline conditions, cloud points ranged between 40–60 °C, while in acidic medium no LCST was found due to the protonation of the amine of the THOX moieties. Additional cytotoxicity assays confirmed a high biocompatibility of PTHOXMA and haemolysis and aggregation assays proved that the thiomorpholine oxide-derived polymers did not cause aggregation or lysis of red blood cells. These preliminary results bode well for the use of PTHOXMA as smart material in biological applications.