Abstract

Abstract

The electrochemical behaviour of the flavonoid naringenin (NGN) was investigated for the first time by cyclic voltammetry (CV), using a disposable electroactivated pencil graphite electrode (PGE*). In this electrochemical sensor, NGN is irreversibly oxidized, giving rise to two pH-dependent peaks due to mixed (diffusion- and adsorption-controlled) electrode processes involving the same number of electrons and protons, namely two and one, respectively. Exploiting these peaks, differential pulse voltammetry (DPV) and square wave voltammetry (SWV) at PGE* in 0.05 mol L-1 potassium hydrogen phthalate were applied for quantitative determination of NGN. The new proposed methods presented linear ranges covering more than three orders of magnitude (7.86 x 10(-8) to 1.82 x 10(-4) mol L-1 NGN for DPV and 7.50 x 10(-8) to 1.00 x 10(-4) mol L-1 NGN for SWV) and low limits of detection (LoD) and quantification (LoQ) (LoD = 3.06 x 10(-8) mol L-1, LoQ = 1.02 x 10(-7) mol L-1 NGN for DPV and LoD = 4.40 x 10(-8) mol L-1, LoQ = 1.11 x 10(-7) mol L-1 NGN for SWV), similar to or better than those reported in the literature. The developed voltammetric methods were applied with good results to determine the intermediate antioxidant power polyphenolics content expressed as mg naringenin equivalent per L grapefruit juice.

Abstract

The goal of the present work was to study the influence of winemaking procedures and the effect of bottle-aging on the antioxidant activity and on the variation of low molecular weight phenolics of Feteasca Neagra and Negru Aromat red wine from the Valea Calugareasca vineyard, Romania. The free radical-scavenging activity was measured using the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical from bottles sampled every 3 months up to the 9th month. The results indicated that Negru Aromat obtained by classical maceration had the highest activity at 6th month. The highperformance liquid chromatography results showed that the most abundant low molecular weight phenolic compounds were catechin, (-)-epicatechin, gallic acid, malvidin, and peonidin 3-O-glucoside. For the phenolics, Feteasca Neagra prepared by classical maceration and Negru Aromat by run-off juice were the richest. For anthocyanidins, the Feteasca Neagra and Negru Aromat wine by classical maceration had the highest concentrations. These results suggest that classical maceration is the winemaking procedure of choice to obtain the highest quality wine from the Valea Calugareasca vineyard.

Abstract

Abstract

Abstract

An optimized electrochemical sensor was developed to assess the antioxidant capacity of carotenoids, accumulating during the life cycle of Haematococcus pluvialis cell cultures. The sensor was improved with a composite renewable surface made of immobilised phosphatidylcholine (PC) on magnetic nanobeads of iron oxide (Fe3O4) and PC/Fe3O4, and it was used to monitor the antioxidant properties of the ketocarotenoid astaxanthin against in situ generated phosphatidylcholine lipoperoxides. The surface configuration was able to mimic the natural position and orientation of astaxanthin in the cellular membrane, conferring to the whole experimental set-up good sensitivity for reactive oxygen species (limit of detection for peroxyl radicals 9.1 x 10(-10) mol L-1) with a linear response ranging between 10(-8) and 1.6 x 10(-6) mol L-1. The sensor has been proved suitable for both batch and flow measurements. The accuracy of the flow measurements was unaffected by the magnetic field intensity. Electrochemical measurements confirmed that natural astaxanthin is a more effective antioxidant than synthetic astaxanthin, vitamin E and lutein and the protective effect of astaxanthin correlates with its concentration inside the cell. The newly developed sensor is hence useable for in-line monitoring of whole-cell based industrial bioprocesses for the production of astaxanthin.

Abstract

In this work a novel sensor array platform based on a dual carbon screen-printed electrode was developed for the simultaneous determination of chlorogenic acid and caffeine. One of the carbon working electrodes was modified with platinum nanoparticles, reduced graphene oxide and laccase (C-SPE/Pt-NPs/RGO/lacc-biosensor) for chlorogenic acid determination and the second carbon working electrodes was modified with reduced graphene oxide and Nafion (C-SPE/RGO/Nafion-sensor) for caffeine determination. Cyclic voltammetry was used to characterise and optimise the dual sensor array while chronoamperometry was used to investigate the bioelectrocatalytic response. The C-SPE/Pt-NPs/RGO/lacc for biosensing chlorogenic acid exhibited a sensitivity of 0.02 mu A mu M (1) and a detection limit of 2.67 mu M whereas the C-SPE/RGO/Nafion used for sensing caffeine has showed a sensitivity of 1.38 mu A mu M-1 and a detection limit of 0.22 mu M. The developed sensor array was used to determine these two major coffee bean compounds from real coffee samples. Due to its simplicity, feasibility and accessibility, the developed dual sensor array could represent the basis of a valuable analytical tool able to screen both chlorogenic acid and caffeine content from coffee samples offering important information about the phytochemical composition of the samples.

Abstract

The goal of this paper aimed the development of an inexpensive, reliable and easy-to-use biodevice for detection and monitoring of phenol and phenolic endocrine disruptors in water samples. X-Ray (XRD) diffraction technique was employed for physical characterization of the modified electrode surface, results revealing nanostructured layers assemblies of polycrystalline gold with (200) growth preferred orientation and gold crystallite size of 33.19 nm. Investigation of the modified surface charge transfer properties was performed using cyclic voltammetry technique highlighting a significant enhancement of the electron transfer rate. Dual signal amplification offered by synergistic effect of gold nanoparticle and reduced graphene oxide layers and tyrosinase led to competitive detection limits (7.2 x 10(-8) mol L-1 for phenol and 4.8 x 10(-7) mol L-1 for octylphenol) and sensitivities (416 nA/mu mol for phenol and 155 nA/mu mol for octylphenol). The obtained values of the K-m(app) and I-max/K-m(app) ratio confirmed a strongly dependence of the immobilized tyrosinase catalytic efficiency on the steric and electronic properties of the bulky side chain in the para position of the phenolic compound. The biodevice showed a percent recovery between 87 +/- 8% and 94 +/- 11% demonstrating a suitable degree of accuracy and confirming the application potential to the detection and monitoring of phenol and several endocrine disruptors in water samples. (C) 2015 Elsevier B.V. All rights reserved.

Abstract

The present work describes the development of a nanocomposite system and its application in construction of a new amperometric biosensor applied in the determination of total polyphenolic content from propolis extracts. The nanocomposite system was based on covalent immobilization of laccase on functionalized indium tin oxide nanoparticles and it was morphologically and structural characterized. The casting of the developed nanocomposite system on the surface of a screen-printed electrode was used for biosensor fabrication. The analytical performance characteristics of the settled biosensor were determined for rosmarinic acid, caffeic acid and catechol (as laccase specific substrate). The linearity was obtained in the range of 1.06x10(-6) - 1.50x10(-5) mol L-1 for rosmarinic acid, 1.90x10(-7) - 2.80x10(-6) mol L-1 for caffeic acid and 1.66x10(-6) - 7.00x10(-6) mol L-1 for catechol. A good sensitivity of amperometric biosensor 141.15 nA A mu mol(-1) L-1 and fair detection limit 7.08x10(-8) mol L-1 were obtained for caffeic acid. The results obtained for polyphenolic content of propolis extracts were compared with the chromatographic data obtained by liquid-chromatography with diode array detection.

Abstract

A fluorimetric method for the determination of cysteine (CSH) and cystine (CSSC) at nanomolar concentrations is reported. The detection limit was 2.46x10(-11) M for CSH when derivatisation is performed by 5-iodoacetamidofluorescein (5-IAF) and respectively 7.2x10(-10) M when monobromobimane was used as fluorescent reagent. The dynamic range of analytical response was 3x10(-10) - 3x10(-8) M ( in the case of CSH-5-IAF). The method was further applied to determine the [CSH]/[CSSC] ratio at nanomolar concentration levels as potential marker of aminoacids oxidative status. An original algorithm to calculate the exact concentrations for each form was established, being provided even the experimental data to support it. Zinc influence on avoiding CSH oxidation was studied. Data were confirmed by high-performance liquid chromatography with fluorescence detection.