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Sterigmatocystin is a carcinogenic compound that affects several species of crops and several species of experimental animals. The sterigmatocystin biosynthetic pathway is the best known and most studied. The International Agency for Research on Cancer classifies sterigmatocystin in the Group 2B. Three groups of analytical methods to determine sterigmatocystin in food can be found: chromatographic, ELISA immunoassays and chemical sensors. In addition, sterigmatocystin is a precursor of aflatoxin B 1 in those cases where cereals and/or food are contaminated with fungi capable of producing aflatoxins. Chemical structures of sterigmatocystin and aflatoxin B 1 are similar. These mycotoxins are pathogens of animals and cereals, producing a major economic impact on biotechnology and agricultural and food industries. This review summarizes different aspects related to sterigmatocystin such as its biosynthesis, toxicological studies and analytical methods for its determination., (Copyright © 2018. Published by Elsevier Ltd.)

The goal of achieving food safety and quality has become increasingly important in relevant areas. The achievement of this objective includes a significant effort in different areas related to the production of raw materials, storage, transportation, etc. One of the central areas in the verification of food safety and food quality control is related to the analysis of food components and, in particular, possible toxic substances that they may contain. Therefore, the demand for appropriate methods for the determination of these substances is increasingly demanding. Thus, not only is accuracy and precision sought in the results of the analysis, but also the speed, simplicity and lowering of costs. In this way, electrochemical techniques and, particularly, electrochemical biosensors have emerged in recent times as good candidates to satisfy such requirements. This review summarizes the advances made in research and development centers located in South American countries related to the development of electrochemical biosensors for the determination of toxic substances present in foods, particularly mycotoxins and herbicides. [ABSTRACT FROM AUTHOR]

Electrochemical sensors and biosensors are analytical tools, which are in continuous development with the aim of generating new analytical devices which are more reliable, cheaper, faster, sensitive, selective, and robust than others. In matrices related to agroalimentary, environmental, or health systems, natural or synthetic compounds occur which fulfil specific roles; some of them (such as mycotoxins or herbicides) may possess harmful properties, and others (such as antioxidants) beneficial ones. This imposes a challenge to develop new tools and analytical methodologies for their detection and quantification. This review summarises different aspects related to the development of electrochemical sensors and biosensors carried out in Argentina in the last ten years for application in agroalimentary, environmental, and health fields. The discussion focuses on the construction and development of electroanalytical methodologies for the determination of mycotoxins, herbicides, and natural and synthetic antioxidants. Studies based on the use of different electrode materials modified with micro/nanostructures, functional groups, and biomolecules, complemented by the use of chemometric tools, are explored. Results of the latest reports from research groups in Argentina are presented. The main goals are highlighted. [ABSTRACT FROM AUTHOR]

Abstract: The development of an electrochemical immunosensor incorporated in a micro fluidic cell for quantification of citrinin (CIT) mycotoxin in rice samples is described for the first time. Both CIT present in rice samples and immobilized on a gold surface electrodeposited on a glassy carbon (GC) electrode modified with a cysteamine self-assembled monolayer were allowed to compete for the monoclonal mouse anti-CIT IgG antibody (mAb-CIT) present in solution. Then, an excess of rabbit anti mouse IgG (H+L) labelled with the horseradish peroxidase (secAb-HRP) was added, which reacts with the mAb-CIT which is in the immuno-complex formed with the immobilized CIT on the electrode surface. The HPR, in the presence of hydrogen peroxide (H2O2) catalyzes the oxidation of catechol (H2Q) whose back electrochemical reduction was detected on a GC electrode at −0.15V vs Ag/AgCl by amperometric measurements. The current measured is proportional to the enzymatic activity and inversely proportional to the amount of CIT present in the rice samples. This immunosensor for CIT showed a range of work between 0.5 and 50ngmL−1. The detection (LOD) and the quantification (LOQ) limits were 0.1 and 0.5ngmL−1, respectively. The coefficients of variation intra- and inter-assays were less than 6%. The electrochemical detection could be done within 2min and the assay total time was 45min. The immunosensor was provided to undertake at least 80 determinations for different samples with a minimum previous pre-treatment. Our electrochemical immunosensor showed a higher sensitivity and reduced analysis time compared to other analytical methods such as chromatographic methods. This methodology is fast, selective and very sensitive. Thus, the immunosensor showed to be a very useful tool to determine CIT in samples of cereals, mainly rice samples. [ABSTRACT FROM AUTHOR]

• A label free electrochemical immunosensor is developed to determine mycotoxin patulin for the first time. • A glassy carbon electrode modified with graphene oxide was used to immobilize the anti-patulin antibody. • The patulin determination in apple juice was performed by electrochemical impedance spectroscopy. • Results obtained with the electrochemical immunosensor were compared with those obtained by HPLC measurements. In this work, an electrochemical immunosensor to determine patulin mycotoxin in apple juice is developed. It consists of a glassy carbon electrode modified with a dispersion of graphene oxide and polyclonal anti-patulin antibodies bound to their oxygenated groups. Patulin determination was performed by electrochemical impedance spectroscopy. The calibration curve is linear for a concentration range from 1 × 10−2 to 10 ng mL−1. The limit of detection and the concentration of patulin to obtain 50% inhibition (IC 50) were 9.8 pg mL−1 and 360 pg mL−1, respectively. In addition, an acceptable accuracy, with a percentage coefficient of variation (%CV) close to 20%, and recovery percentage (%R) of 86% were found. The electrochemical immunosensor has the advantage of allowing the determination of patulin without any pre-treatment of the samples. The results obtained from the electroanalytical technique were compared with those obtained by HPLC. [ABSTRACT FROM AUTHOR]

A highly sensitive electrochemical sensor based on self-assembled monolayers (SAMs) of cysteamine on gold electrodes (Au-CA) in pH 4 citrate buffer solutions was developed to quantify the moniliformin (MON) mycotoxin by cyclic voltammetry in contaminated maize samples. Parameters of SAMs modified gold electrodes such as concentration of thiol, modification time and MON accumulation time were adjusted to obtain the best performance of the sensor. The calibration curve was linear in the MON concentration range from 1 × 10 −9 to 1 × 10 −7 mol L −1 . A limit of detection of 8.3 × 10 −10 mol L −1 (0.1 ppb) was obtained. The standard addition method was used to minimize matrix effects. The concentration of MON determined with the electrochemical sensor was in very good agreement with results found by HPLC UV–vis. The sensor showed a good analytical performance with a relative standard deviation (RDS%) of about 3%. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of sterigmatocystin in acetonitrile + 0.1 M tetrabutylammonium perchlorate at glassy carbon electrodes is studied for the first time using cyclic and square wave voltammetries, and controlled-potential electrolysis. Two reduction peaks centered at − 1.77 and − 2.33 V vs. Ag/AgCl were found, which correspond to the formation of the radical anion and dianion, respectively. The overall electrode process was diffusion controlled. The initially formed radical anion undergoes an irreversible dimerization reaction with a rate constant of 2.06 × 10 4 M − 1 s − 1 , producing a basic dimeric dianion, which is protonated by the starting molecule. An unstable dimeric reaction product was detected by UHPLC-MS/MS measurements. A value of (3.1 ± 0.9) × 10 − 5 cm 2 s − 1 was calculated for sterigmatocystin diffusion coefficient from convoluted cyclic voltammograms. Thermodynamic and kinetics parameters were determined from digital simulation of cyclic voltammograms. Probable chemical structures for the dimer are proposed based on the results of theoretical calculations. The effect of the addition of tetrabutylammonium hydroxide, trifluoroacetic acid and water on the voltammetric signals was also investigated. The quantitative determination of sterigmatocystin was carried out by square wave voltammetry using the commercial reagent. The calibration curve was linear in the concentration range from 0.050 to 11.2 ppm, and the limits of detection and quantification were 10 and 33 ppb for signal to noise ratios of 3:1 and 10:1, respectively. [ABSTRACT FROM AUTHOR]

The electrochemical oxidation of moniliformin (MON) mycotoxin in acetonitrile (ACN) + 0.1 mol dm −3 (C 4 H 9 ) 4 NPF 6 at electrochemically pretreated glassy carbon electrodes (EPGCE) and fiber disk carbon ultramicroelectrodes (FCUME) is studied for the first time. Electrochemical techniques used were cyclic (CV), convolution and square wave (SWV) voltammetries as well as controlled potential electrolysis. Experimental results allowed inferring a complex electro-oxidation mechanism with adsorption of reactant and homogeneous chemical steps coupled to the electron transfer reaction. The UV–Vis spectroscopy was used as a non-electrochemical technique in order to follow the disappearance/appearance of the reactant/reaction product/s during controlled potential electrolysis. The most probable electro-oxidation mechanism proposed on the base of digital simulation results of cyclic voltammograms is one of the CEC type. Thermodynamic and kinetics parameters were calculated from the fitting of experimental cyclic voltammograms, while the diffusion parameter was calculated from convoluted cyclic voltammograms. We propose that reaction products obtained are produced through the decomposition of the MON radical generated from the electrochemical oxidation of MON anion. On the other hand, the MON quantitative determination was performed using adsorptive SWV at EPGCE. An extremely low detection limit of 1 × 10 −11 mol dm −3 (1.2 ppt) for a signal to noise ratio of 3:1 was calculated. [ABSTRACT FROM AUTHOR]

Abstract: An amperometric biosensor based on horseradish peroxidase (EC1.11.1.7,H2O2-oxide-reductases) to determine the content of citrinin mycotoxin in rice samples is proposed by the first time. The method uses carbon paste electrodes filled up with multi-walled carbon nanotubes embedded in a mineral oil, horseradish peroxidase, and ferrocene as a redox mediator. The biosensor is covered externally with a dialysis membrane, which is fixed to the body side of the electrode with a Teflon laboratory film, and an O-ring. The reproducibility and the repeatability were of 7.0% and 3.0%, respectively, showing a very good biosensor performance. The calibration curve was linear in a concentration range from 1 to 11.6nM. The limits of detection and quantification were 0.25nM and 0.75nM, respectively. For comparison, the citrinin content in rice samples was also determined by fluorimetric measurements. A very good correlation was obtained between the electrochemical and spectrophotometric methods. [Copyright &y& Elsevier]

Abstract: We study the thermodynamics and kinetics of the adsorption of a redox couple having quinone nature on glassy carbon electrodes. This couple is produced by the anodic oxidation of mycotoxin ochratoxin A in 10% acetonitrile+90% 1M HClO4 aqueous solution. The quasi-reversible redox couple was studied by both cyclic (CV) and square wave (SWV) voltammetric techniques. The Frumkin adsorption isotherm best described the specific interaction of the redox couple with carbon electrodes. By fitting the experimental data, we obtained values of −28.4kJmol−1 and 0.70±0.02 for the Gibbs free energy of adsorption and the interaction parameter, respectively. SWV fully characterized the thermodynamics and kinetics of the adsorbed redox couple, using a combination of the “quasi-reversible maximum” and the “splitting of SW peaks” methods. Average values of 0.609±0.003V and 0.45±0.06 were obtained for the formal potential and the anodic transfer coefficient, respectively. Moreover, a formal rate constant of 10.7s−1 was obtained. SWV was also employed to generate calibration curves. The lowest concentration of mycotoxin was 1.24×10−8 M (5ppb), measured indirectly with a signal to noise ratio of 3:1. [Copyright &y& Elsevier]

The electro-oxidation of alternariol monomethyl ether (AME), one of the main metabolites of the Alternaria genus mycotoxins, is studied at 1-dodecanethiol (DDT)-modified gold electrodes, in acetonitrile (ACN) – aqueous phosphate buffer solutions of different pH values, by using cyclic (CV) and square-wave (SWV) voltammetries. The AME voltammetric response at the bare electrode suffers from two drawbacks: it appears at potentials close to the onset of gold oxide formation, and it is hampered by a fouling of the electrode surface due to the accumulation of oxidized products. These shortcomings are circumvented by the use of DDT-coated electrodes, since the intervening monolayer inhibits gold oxide formation and surface passivation by the electrochemical products, without affecting the oxidation kinetics of AME significantly. Diagnostic criteria based on the voltammetric peak parameters show that the electrochemical behavior of AME at the modified electrode is mainly controlled by reactant diffusion from solution, with a weak adsorption of both the mycotoxin and its oxidation products at monolayer defects. Calibration curves were constructed from the AME square-wave voltammetric response and a detection limit of 9.1 × 10-8 mol dm-3 was determined, which is about three times smaller than a previous estimate at platinum and glassy carbon electrodes, and about fifty times smaller than the limit derived from measurements carried out at a polyphenol oxidase-modified carbon paste electrode. [Copyright &y& Elsevier]