New potentiometric microbial biosensor for ethanol determination in alcoholic beverages

A potentiometric oxygen electrode was successfully used to produce a microbial biosensors with an extended response range, based on immobilised yeast cells (Saccharomyces ellipsoideus). The response for ethanol takes ca. 7 min for the steady-state method and 2 min for kinetic measurements. A linear calibration achieved over more than two decades of ethanol concentration. Selective determination of ethanol in the presence of non-volatile compounds was achieved using a second PTFE membrane to cover the biocatalytic layer.     

Mechanism of pyridine protonation in water clusters of increasing size

This work presents a theoretical mechanistic study of the protonation of pyridine in water clusters, at the B3LYP/cc-pVDZ theory level. Clusters from one to five water molecules were used. Starting from previously determined structures, the reaction paths for the protonation process were identified. For complexes of pyridine with water clusters of up to three water molecules just one transition state (TS) links the solvated and protonated forms. It is found that the activation energy decreases with the number of water molecules. For complexes of four and five water molecules two transition states are found. For four water molecules, the first TS links the starting solvated structure with a new, less stable, solvated form through a concerted proton transfer between a ring of water molecules. The second TS links the new solvated structure to the protonated form. Thus, protonation is a two-step process. For the five water molecules cluster, the new solvated structure is more stable than the starting one. This structure exhibits two double hydrogen bonds involving the pyridinic nitrogen and several water molecules. The second TS links the new structure with the protonated form. Now the process occurs in one step. In all cases considered, the proton transfers involve an interconversion between covalent and hydrogen bonds. For four and five water molecules, the second TS is structurally and energetically very close to the protonated form. As evidenced by the vibration frequencies, this is due to a flat potential energy hypersurface in the direction of the reaction coordinate. Determination of DeltaG at 298.15 K and 1 atm shows that the protonation of pyridine needs at least four water molecules to be spontaneous. The complex with five water molecules exhibits a large DeltaG. This value yields a pKa of 2.35, relatively close to the reported 5.21 for pyridine in water.     

Magnetic beads-based immunoassay as a sensitive alternative for atrazine analysis

A new immunoassay strategy for sensitive atrazine determination based on magnetic beads is reported. The immuno-method is a competitive solid-phase immunoassay where the anti-atrazine antibody is immobilized on the magnetic beads surface and fixed at the reaction cell bottom using a simple magnet, which generates a magnetic field. Analyte and HRP (horseradish peroxidase) tracer compete for active sites of antibody. After the immunointeractions antibody-analyte and antibody-tracer, atrazine quantification from the sample is performed by injection of the chemiluminescence substrate (luminol, hydrogen peroxide and p-iodophenol). Different antibodies (polyIgG anti-atrazine Ab I and affinity purified polyIgG anti-atrazine AbI) were tested in this configuration. Also, optimum concentration of antibody-covered magnetic beads was set up (8 mg/l Ab II). Finally, the performance of magnetic beads-based immunoassay for atrazine determination was evaluated demonstrating that the magnetic beads-based immunoassay is one of the most sensitive method for atrazine determination (LoD = 3 pg/l, IC₅₀ = 37 pg/l, DR = 10-1000 pg/l).     

Building switchable peptide-architectures on gold/composite surfaces: New perspectives in electrochemical bioassays

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Paper-based diagnostic platforms and devices

Paper-based analytical devices have become lately “must have” components in equipment and instrumental designed for point-of-care applications, especially when they are used in tandem with microfluidic platforms. Nowadays, paper-based electrochemical devices (PEDs) represent the first choice in the development of lab-on-a-chip biosensors because of their benefits in biomedical diagnosis in terms of simplicity, affordability, portability, and disposability. Moreover, cellulose is a biodegradable and biocompatible substrate, ideal for building disposable devices for use in remote locations or low-resource settings. Despite their low costs and simplicity, PEDs must face a tough challenge—meeting the affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverable to end users criteria. The latest achievements in microfluidic PEDs for clinical diagnosis will be critically discussed, putting emphasis on innovative assay formats and methods for surface modification.     

Plasma generation in liquid as a new efficient synthesis approach of titania–zinc ferrite nano(photo)catalyst

In the past years, an important problem that requires solutions at the global scale is the environmental pollution. This work describes a possible approach toward finding such solutions based on nanophotocatalysts with improved activity. Thus, the present study reports a new and efficient synthesis procedure for titania–zinc ferrite nanocomposite with enhanced photodegradation activity. The method is based on the liquid phase plasma technique and follows a bottom-up scheme. The resulted materials have been compared with those synthesized by the ultrasound-assisted method. Using the plasma-assisted procedures in the fabrication of an efficient nano(photo)catalyst decreases considerably the reaction time. The liquid phase plasma generates nanoparticles with enhanced structural, textural, and morphological properties as demonstrated by X-ray diffraction, nitrogen sorption, transmission electron microscopy, and small-angle X-ray scattering.     

Conductometric determination of ammonium by a multisyringe flow injection system applying gas diffusion

A multisyringe flow injection system (MSFIA) coupled to a gas-diffusion cell has been developed for the conductometric determination of ammonium in different water samples. Operation strategies, membrane, reagent concentrations, and flow rates have been studied to optimize the sensitivity of detection and to fit the required working range. The proposed MSFIA system has been compared with former FIA and SIA systems using gas diffusion. The system was applied to the determination of ammonium in water samples of different matrices in order to evaluate its performance. These samples were coastal waters, pond waters, and compost aqueous extracts. Good recoveries of 102?±?13% were obtained and no significant differences with the reference methods were found. The system can be used for a wide concentration range of ammonia, from 0.075 to 360?mg?L^?1, without sample dilution and with a precision better than 2% of RSD. The throughput of the method was 32 injections per hour.     

Synthesis and characterization of the inclusion complex between repaglinide and sulfobutylether-β-cyclodextrin (Captisol®)

An inclusion complex between repaglinide and a cyclodextrin derivative, 7-sulfobutylether-β-cyclodextrin (Captisol^®) was synthesized and characterized taking into account its possible benefits regarding the solubility, thus the bioavailability of repaglinide (an oral antidiabetic, carbamoyl methyl benzoic acid, practically insoluble in water, used for the treatment of type II diabetes mellitus). In order to establish the optimal conditions for the synthesis, phase-solubility studies were performed. Their results (A_L type phase-solubility diagram), as well as the chromatographic retention behavior of repaglinide in the presence of Captisol^® indicated that an 1:1 inclusion complex is formed. The estimated apparent stability constant, according to the Higuchi-Connors method is 530 M^?1. These data were confirmed by ¹H-NMR, IR, DTA of the inclusion complex prepared through lyophilization.     

Experimental thermal characterization of timber frame exterior wall using reed straws as heat insulation materials

Journal of Thermal Analysis and Calorimetry - The research presented in this paper proposes structures of timber frame exterior walls using reed straws as insulation materials. Having thicknesses...