Electrochemical signatures of multivitamin mixtures

The ability of cyclic square wave voltammetry to identify distinct fingerprints of multiple vitamins, in a single voltammetric run, is demonstrated. This method represents an efficient alternative to more common techniques for fast screening of complex vitamin mixtures or commercial tablets due to its low cost, high speed and sensitivity

Electrospun Nanofibers as Selective Barrier to the Electrochemical Polyphenol Oxidation

A tissue made of nylon-6 electrospun nanofibers has been fabricated and placed over a glassy carbon electrode. The resulting coating eliminates the passivation effect of the electrode surface caused by polyphenols oxidation, while the characteristic waves of small biological antioxidants are not affected

Interfacial rheology study of espresso coffee foam structure and properties

The espresso coffee beverage is a polyphasic colloidal system, in which the liquid phase is topped by a wet foam of tiny sphere-shaped gas bubbles. Each sphere is surrounded by a liquid film (lamellae) that isolates it from its neighbours and that hosts biopolymers and natural surfactants. Foaming biopolymers of coffee (total fraction and its sub-fractions: proteins/melanoidins fraction and polysaccharides fraction) were extracted from defatted and raw, commercially roasted ground coffee. In order to study the viscoelastic behaviour of the surface-adsorbed layer, all the extracted fractions were analyzed using a commercial interfacial rheometer CIR 100 operating in time sweep mode. The growth of the interfacial elasticity of the lamella implicitly contains all the information about the molecular interaction at the foam air/liquid interface. These interactions are described to be responsible for the foam stabilization. Results indicate that the kinetics of the film formation is mediated by the polysaccharide component and that the protein/melanoidin component of the coffee foaming fraction exhibits the highest viscoelastic interfacial properties. Lipids play a major role in the interfacial film formation due to their interaction with protein-like macromolecules, the melanoidins. A correlation was established between air/water interface properties of the foaming systems and the respective foam volumes evaluated by means of the image analysis. A new mathematical description of surface viscoelastic phenomena, covering the terms of transport of surfactant biopolymers to the interface and describing the coagulation of particles here taking place, is proposed. The suggested equation overcomes the Warburton model, taking into account the complexity of real food systems as in the case of the espresso coffee beverage

Rheological interfacial properties of espresso coffee foaming fractions

La stabilit\ue0 e la velocit\ue0 di formazione della schiuma del caff\ue8 espresso sono legate alla cinetica di formazione e alla viscoelasticit\ue0 di tale film biopolimerico che si forma all\u2019interfaccia delle bolle. Le principali macromolecole responsabili della schiuma del caff\ue8 espresso, complessi melanoidine/proteine e polisaccaridi, sono state estratte dalla polvere di caff\ue8 ed analizzate sia per la loro attitudine alla formazione della schiuma (analisi della morfologia della schiuma) , sia per le propriet\ue0 di strutturazione all\u2019interfaccia liquido/aria, valutate tramite reologia interfacciale

Adaptive nanowire\u2013nanotube bioelectronic system for on-demand bioelectrocatalytic transformations

An integrated nanobioelectronic system, exploiting the distinct properties of nanowires and carbon-nanotubes, has been designed for triggering reversibly and on-demand bioelectrocatalytic transformations of alcohols

Estrazione e caratterizzazione strutturale della frazione polisaccaridica estratta dall\u2019essudato di Launaea Acanthodes

Mediante analisi di light scattering, tecniche mono e bidimensionali di spettroscopia NMR e viscosimetria capillare la \ue8 stata caratterizzata la frazione polisaccaridica dell\u2019essudato di Launaea Acanthodes. Le analisi strumentali hanno permesso di definire che il polisaccaride \ue8 costituito da unit\ue0 di galattosio, ramnosio, arabinosio e residui di acido galatturonico. E\u2019 stata dimostrata la presenza di strutture aggregate che vengono escluse nel calcolo della distribuzione del peso molecolare. I valori bassi dei raggi idrodinamico e di girazione indicano una compattezza strutturale delle macromolecole nelle condizioni di analisi. Il polimero possiede una conformazione random-coil ad elevata densit\ue0 strutturale. Una via utile per investigare le capacit\ue0 di strutturazione dell\u2019arabinogalattano allo studio \ue8 stata la produzione di sottili pellicole di polimero ottenute per evaporazione dl solvente. I film ottenuti si presentano opachi e con scarse propriet\ue0 meccaniche: elevata fragilit\ue0, elasticit\ue0 e resistenza alla trazione scarse. L\u2019indagine morfologica tramite SEM indicano una struttura non uniforme, priva di una precisa orientazione dei polimeri

Nylon Nanofibrous Biosensors for Glucose Determination

Nanofibrous membranes have been produced by electrospinning to develop first generation glucose biosensors. The direct immobilization of glucose oxidase onto the polyamide nanofibrous surfaces by drop coating revealed a simple and efficient method for the development of sensitive, stable, and reproducible electrochemical biosensors. The biosensor showed a linear response over the range 1 – 9X10-3 glucose (R-2=0.9997) with a sensitivity of 1.11 muA/mM and a limit of detection of 2.5X10-6 M (S/N=3). The uncertainty of repeatability was 2% (RSD%, n=30). After one month of storage, the signal decreased of 35%. The recovery of glucose, evaluated in real samples of honey, was 98% (RSD%=1%, n=3)

On-demand protection of electrochemical sensors based on adaptive nanowires

We report here on the use of adaptive nanowires for addressing the key surface fouling problem of electrochemical sensors. Effective resistance against surfactant fouling is obtained by switching magnetically the surface orientation of alkanethiol-coated gold nanowires (containing a short nickel segment) between horizontal and vertical positions to allow the transducer to perform the measurement and reset it to the protection mode between successive measurements. This leads to "opening" and "closing" of the surface and hence switching between active (sensing) and passive (protection) modes. Such on-demand protection and minimization of surface-fouling are indicated from prolonged series of stripping-voltammetric measurements of cadmium in the presence of gelatin, albumin, or Tween80. Factors influencing the protective action of the adaptive nanowires, including the length of the alkanethiol layer or of the gold/nickel segments were examined and optimized. Such on-demand protection capability should facilitate practical sensing applications of electrochemical devices

Electrospun nonwoven nanofibrous membranes for sensors and biosensors

This review will focus on the recent advances on nanofibrous membranes (NFM) prepared by electrospinning (ES) applied to modify electrochemical sensors and biosensors. Most relevant applications of NFM include their used as selective barrier toward diffusion, protective coatings against fouling, conductive substrates for sensing applications, catalytic and biocatalytic membranes. The main advantages and drawbacks of these applications are critically assessed

Striped Alloy Nanowire Optical Reflectance Barcodes Prepared from a Single Plating Solution

The preparation of multisegment alloy nanowire barcodes with optical-reflectance striping patterns and large coding capacity using a template-assisted electro-deposition from a single gold-silver plating solution, was presented. A template-assisted electro-deposition method can be applied in a predetermined order for different duration for producing alloy segment of controlled length. The nanowire was prepared from an 85/15 (v/v) Au/Ag plating solution by applying different potentials. Barcodes were prepared by varying the deposition conditions, while using the same plating solution. The multipotential templated deposition from plating solution resulted in distinct stepwise variation of the alloy composition along the length of the nanowires. The reflectance intensity of barcodes was determined using the highest intensity value corresponding to a prevalently silver segment deposited at -0.50 V