Bioelectrochemical evaluation of plant extracts and gold nanozyme-based sensors for total antioxidant capacity determination.

The antioxidant properties of different plant extracts are usually claimed and used by food, medicine and cosmetic industry due to their health promoting capacities. In this study the presence of antioxidant compounds and the total antioxidant capacity of water-soluble extracts, prepared using two extraction methods and a variety of solvents, have been determined and a rapid screening method has been developed. Plant extracts characterisation, composition and antioxidant properties were confirmed by FTIR and Raman spectroscopies. Voltammetry, amperometry and electrochemical impedance were used to highlight the total antioxidant capacity of each extract using an electrochemical gold nanozyme-sensor based on the enzyme-like catalytic activity of gold nanoparticles. Both anodic area of cyclic voltammograms (10.31 µA V) and electrochemical index (153) calculated using differential potential voltammetry show the total content of antioxidant compounds, allowing to discriminate between different extracts. Amperometric total antioxidant capacity measurements were associated with those from classical chemiluminescence and good correlation has been found (Pearson's correlation coefficient of 0.958).

Binary logistic regression-Instrument for assessing museum indoor air impact on exhibits.

This paper presents a new way to assess the environmental impact on historical artifacts using binary logistic regression. The prediction of the impact on the exhibits during certain pollution scenarios (environmental impact) was calculated by a mathematical model based on the binary logistic regression; it allows the identification of those environmental parameters from a multitude of possible parameters with a significant impact on exhibitions and ranks them according to their severity effect. Air quality (NO2, SO2, O3 and PM2.5) and microclimate parameters (temperature, humidity) monitoring data from a case study conducted within exhibition and storage spaces of the Romanian National Aviation Museum Bucharest have been used for developing and validating the binary logistic regression method and the mathematical model. The logistic regression analysis was used on 794 data combinations (715 to develop of the model and 79 to validate it) by a Statistical Package for Social Sciences (SPSS 20.0). The results from the binary logistic regression analysis demonstrated that from six parameters taken into consideration, four of them present a significant effect upon exhibits in the following order: O3>PM2.5>NO2>humidity followed at a significant distance by the effects of SO2 and temperature. The mathematical model, developed in this study, correctly predicted 95.1 % of the cumulated effect of the environmental parameters upon the exhibits. Moreover, this model could also be used in the decisional process regarding the preventive preservation measures that should be implemented within the exhibition space. IMPLICATIONS: The paper presents a new way to assess the environmental impact on historical artifacts using binary logistic regression. The mathematical model developed on the environmental parameters analyzed by the binary logistic regression method could be useful in a decision-making process establishing the best measures for pollution reduction and preventive preservation of exhibits.

Recent Applications for in Vitro Antioxidant Activity Assay.

This review presents some of the most recent aspects related to antioxidants and the basic kinetic models of inhibited autoxidation and analyzes the chemical principles of antioxidant capacity assays. Taking into account the reactions involved, in the antioxidant activity determinations, the assays can be classified into two main types: hydrogen atom transfer reactions and electron transfer. This review focuses on analytical methods used for antioxidant activity assay, published in the period 2009-2014.

Enantioselective stable isotope analysis (ESIA) - a new concept to evaluate the environmental fate of chiral organic contaminants.

Since 2011, the enantiospecific stable carbon isotope analysis (ESIA) has emerged as an innovative technique to assess the environmental fate of chiral emerging compounds by combining in one experimental technique both compound specific isotope analysis (CSIA) and enantioselective analysis. To date, the ESIA was applied for four classes of compounds: α-hexachlorocyclohexane (α-HCH), polar herbicides (phenoxy acids), synthetic polycyclic musk galaxolide (HHCB), and phenoxyalkanoic methyl herbicides. From an analytical point of view there are factors that are hindering the application of ESIA methods for the field samples: (i.e. amounts of target analyte, matrix effects, GC resolution) and overcoming these factors is challenging. While ESIA was shown as a mature technique for the first three abovementioned class of compounds, no isotope analysis of individual enantiomers could be performed for phenoxyalkanoic methyl herbicides. With respect to field studies, one study showed that ESIA might be a promising tool to distinguish between biotic and abiotic transformation pathways of chiral organic contaminants and even to differentiate between their aerobic and anaerobic biotransformation pathways. The development of ESIA methods for new chiral emerging contaminants in combination with development of multi-element isotope analysis will contribute to a better characterization of transformation pathways of chiral organic contaminants.

Heat shock, visible light or high calcium augment the cytotoxic effects of Ailanthus altissima (Swingle) leaf extracts against Saccharomyces cerevisiae cells.

To gain new insight into the antimicrobial potential of Ailanthus altissima Swingle, ethanol leaf extracts were evaluated for the antifungal effects against the model yeast Saccharomyces cerevisae. The extracts inhibited the yeast growth in a dose-dependent manner, and this effect could be augmented by heat shock, exposure to visible light or exposure to high concentrations of Ca(2+). Using transgenic yeast cells expressing the Ca(2+)-dependent photoprotein, aequorin, it was found that the leaf extracts induced cytosolic Ca(2+) elevation. Experiments on yeast mutants with defects in Ca(2+) transport demonstrated that the cytotoxicity of the A. altissima leaf extracts (AaLEs) was mediated by transient pulses of Ca(2+) ions which were released into the cytosol predominantly from the vacuole. The investigation of the antifungal synergies involving AaLEs may contribute to the development of optimal and safe combination therapies for the treatment of drug-resistant fungal infections.

Development of an enantiomer-specific stable carbon isotope analysis (ESIA) method for assessing the fate of α-hexachlorocyclo-hexane in the environment.

α-Hexachlorocyclohexane (α-HCH) is the only chiral isomer of the eight 1,2,3,4,5,6-HCHs and we have developed an enantiomer-specific stable carbon isotope analysis (ESIA) method for the evaluation of its fate in the environment. The carbon isotope ratios of the α-HCH enantiomers were determined for a commercially available α-HCH sample using a gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) system equipped with a chiral column. The GC-C-IRMS measurements revealed δ-values of -32.5 ± 0.8‰ and -32.3 ± 0.5‰ for (-) α-HCH and (+) α-HCH, respectively. The isotope ratio of bulk α-HCH was estimated to be -32.4 ± 0.6‰ which was in accordance with the δ-values obtained by GC-C-IRMS (-32.7 ± 0.2‰) and elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) of the bulk α-HCH (-32.1 ± 0.1‰). The similarity of the isotope ratio measurements of bulk α-HCH by EA-IRMS and GC-C-IRMS indicates the accuracy of the chiral GC-C-IRMS method. The linearity of the α-HCH ESIA method shows that carbon isotope ratios can be obtained for a signal size above 100 mV. The ESIA measurements exhibited standard deviations (2σ) that were mostly < ± 0.5‰. In order to test the chiral GC-C-IRMS method, the isotope compositions of individual enantiomers in biodegradation experiments of α-HCH with Clostridium pasteurianum and samples from a contaminated field site were determined. The isotopic compositions of the α-HCH enantiomers show a range of enantiomeric and isotope patterns, suggesting that enantiomeric and isotope fractionation can serve as an indicator for biodegradation and source characterization of α-HCH in the environment.

Stable isotope fractionation of gamma-hexachlorocyclohexane (lindane) during reductive dechlorination by two strains of sulfate-reducing bacteria.

Carbon isotope fractionation factors were determined with the dichloro elimination of gamma-hexachlorocyclohexane (gamma-HCH) by the sulfate-reducing bacteria Desulfococcus multivorans DSM 2059 and Desulfovibrio gigas DSM 1382. Both strains are known for cometabolic HCH dechlorination. Degradation experiments with gamma-HCH in concentrations of 22-25 gammaM were carried out using benzoate (for D. multivorans) and lactate (for D. gigas) as electron donors, respectively. Gamma-HCH was dechlorinated by both bacterial strains within four weeks, and the metabolites gamma-3,4,5,6-tetrachlorocyclohexene (gamma-TCCH), chlorobenzene (CB), and benzene were formed. The carbon isotope fractionation of gamma-HCH dechlorination was quantified by the Rayleigh model, using a bulk enrichment factor (epsilon C) of -3.9 +/- 0.6 for D. gigas and -3.4 +/- 0.5 for D. multivorans, which correspond to apparent kinetic isotope effect (AKIEc) values of 1.023 +/- 0.004 or 1.02 +/- 0.003 for stepwise Cl-C bond cleavage. The extent and range of isotope fractionation suggest that gamma-HCH dechlorination can be monitored in anoxic environments by compound-specific isotope analysis (CSIA).

Total antioxidant capacity of some commercial fruit juices: electrochemical and spectrophotometrical approaches.

The aim of this paper was to assess the total antioxidant capacity of some commercial fruit juices (namely citrus), spectrophotometrically and by the biamperometric method, using the redox couple DPPH. (2,2-diphenyl-1-picrylhydrazyl)/DPPH (2,2-diphenyl-1-picrylhydrazine). Trolox was chosen as a standard antioxidant. In the case of the spectrophometric method, the absorbance decrease of the DPPH. solution was followed. For the biamperometric method, the influence of some parameters like the potential difference, DeltaE, DPPH. concentration, and Trolox concentration was investigated. The calibration graph obtained for Trolox presents linearity between 5 and 30 microM, (y=0.059 x + 0.0564, where y represents the value of current intensity, expressed as microA and x the value of Trolox concentration, expressed as muM; r(2)=0.9944). The R.S.D. value for the biamperometric method was 1.29% (n=10, c=15 microM Trolox). In the case of the spectrophotometric method, the calibration graph obtained for Trolox presents linearity between 0.01 and 0.125 mM (y= -9.5789 x+1.4533, where y represents the value of absorbance and x, the value of Trolox concentration, expressed as mM; r(2)=0.9963). The R.S.D. value for the spectrophotometric method was 2.05%. Both methods were applied to total antioxidant activity determination in real samples (natural juices and soft drinks) and the results were in good agreement.

Ascorbic Acid determination in commercial fruit juice samples by cyclic voltammetry.

A method was developed for assessing ascorbic acid concentration in commercial fruit juice by cyclic voltammetry. The anodic oxidation peak for ascorbic acid occurs at about 490 mV on a Pt disc working electrode (versus SCE). The influence of the potential sweep speed on the peak height was studied. The obtained calibration graph shows a linear dependence between peak height and ascorbic acid concentration in the domain (0.1-10 mmol.L(-1)). The equation of the calibration graph was y = 6.391x + 0.1903 (where y represents the value of intensity measured for the anodic peak height, expressed as muA and x the analyte concentration, as mmol.L(-1), r(2) = 0.9995, r.s.d. = 1.14%, n = 10, C(ascorbic acid) = 2 mmol.L(-1)). The developed method was applied to ascorbic acid assessment in fruit juice. The ascorbic acid content determined ranged from 0.83 to 1.67 mmol.L(-1) for orange juice, from 0.58 to 1.93 mmol.L(-1) for lemon juice, and from 0.46 to 1.84 mmol.L(-1) for grapefruit juice. Different ascorbic acid concentrations (from standard solutions) were added to the analysed samples, the degree of recovery being comprised between 94.35% and 104%. Ascorbic acid determination results obtained by cyclic voltammetry were compared with those obtained by the volumetric method with dichlorophenol indophenol. The results obtained by the two methods were in good agreement.

Mercury Determination in Fish Samples by Chronopotentiometric Stripping Analysis Using Gold Electrodes Prepared from Recordable CDs.

A simple method for manufacturing gold working electrodes for chronopotentiometric stripping measurements from recordable CD-R's is described. These gold electrodes are much cheaper than commercially available ones. The electrochemical behavior of such an electrode and the working parameters for mercury determination by chronopotentiometric stripping analysis were studied. Detection limit was 0.30 µg Hg/L and determination limit was 1.0 µg Hg/L for a deposition time of 600 s. Using the developed working electrodes it was possible to determine the total mercury in fish samples. A method for fish sample digestion was developed by using a mixture of fuming nitric acid and both concentrated sulfuric and hydrochloric acids. The recovery degree for a known amount of mercury introduced in the sample before digestion was 95.3% (n=4).

Determination of mercury in fish tissue using a minianalyzer based on cold vapor atomic absorption spectrometry at the 184.9 nm line.

A sensitive method was proposed and optimized for the determination of total mercury in fish tissue by using wet digestion, followed by cold vapor atomic absorption spectrometry (CVAAS) at the main resonance line of mercury (184.9 nm). The measurements were made using a new type of a non-dispersive mercury minianalyzer. This instrument was initially designed and built for atmospheric mercury-vapor detection. For determining mercury in aqueous samples, the minianalyzer was linked with a mercury/hydride system, Perkin Elmer Model MHS-10. To check the method, the analyzed samples were spiked with a standard solution of mercury. The recoveries of mercury spiked to wet fish tissue were >90% for 0.5 - 0.8 g samples. The results showed a better sensitivity (about 2.5 times higher) when using the mercury absorption line at 184.9 nm compared with the sensitivity obtained by conventional CVAAS at 253.7 nm.

Organophosphorus insecticides extraction and heterogeneous oxidation on column for analysis with an acetylcholinesterase (AChE) biosensor.

This paper presents an analysis method for organophosphorus insecticides based on AChE biosensors coupled with a preconcentration and oxidation on a solid phase column. Three organic solvents, acetonitrile (ACN), ethanol and methanol were tested for their influence on AChE activity, insecticide inhibition and their ability to elute the adsorbed insecticides. Our results showed that ACN in a concentration of 5% (v/v) had the less negative effect on biosensor analysis and was the most appropriate organic solvent for the column elution. The presence of the organic solvent in the incubation media of the biosensor was found to induce a reduction of the inhibition percentages. The inhibition of the biosensors was performed in phosphate buffer with 5% (v/v) ACN, while the initial and remaining response of the biosensors were measured in PBS. In these conditions, the LODs of paraoxon and dichlorvos were measured with or without a preconcentration step. The LODs of the AChE biosensor without sample preconcentration were 8 x 10(-8) M for paraoxon and 1 x 10(-7) M dichlorvos and the LOD obtained after the preconcentration step were 2.5 x 10(-8) M for paraoxon and 2.5 x 10(-8) M for dichlorvos. Moreover, the use of the column allowed the heterogeneous oxidation of organophosphorus insecticides for improved LOD.

Versatile method of cholinesterase immobilisation via affinity bonds using Concanavalin A applied to the construction of a screen-printed biosensor.

Development of new and more reliable methods to immobilise biomolecules has emerged rapidly due to a continuous need for more stable, sensitive and reliable biosensors. This paper reports a new method of acetylcholine-esterase (AChE) immobilisation based on the high affinity interaction between the glycoproteic enzyme and Concanavalin A (Con A). In order to establish the nature of the link formed between the glycoenzyme, lectin and support, three different configurations are presented. The optimum immobilisation procedure was further used for biosensor manufacturing. The non-specific adsorption is around 3% and the chemical cross-linking of the proteins is avoided. The optimised method allows loading of the working electrode surface with different amounts of enzyme ranging from 0.3 to 3.3 mIU with a good operational stability. The sensor showed a linear response range to acetylthiocholine substrate between 10 and 110 micromol l(-1) with a sensitivity of 3.6 mA l mol(-1). The applicability of the method to the detection of organophosphorus insecticides resulted in a detection limit of 10(-8) mol l(-1) for chlorpyriphos.