Electrochemical determination of Saccharomyces cerevisiae sp using glassy carbon electrodes modified with oxidized multi-walled carbon nanotubes dispersed in water -Nafion®.

The electrochemical behavior of Saccharomyces cerevisiae sp was studied using a glassy carbon electrode (GCE) modified with Nafion-dispersed oxidized multi-walled carbon nanotubes (OMWCNT). The morphology was studied using scanning electron microscopy (SEM), showing that the yeast sticks to the carbon nanotube surface instead of the glassy carbon surface. The redox couple Fe(CN)6 4-/Fe(CN)6 3- was used to determine the electroactive area and the heterogeneous transfer constant, which increased 80.5% and 108% respectively by the presence of nanotubes. The studies of the pH effect showed that the anodic potential decreases at alkaline pH and that the highest current intensity occurs at a pH value of 7.00. Studies of the scan rate effect have shown that yeast oxidation is an irreversible mixed control process in which two electrons participate. The relationship between yeast concentration and the anodic current density was studied using different electrochemical techniques obtaining the best analytical parameters through chronoamperometry. The linear range was between 3.36 and 6.52 g L-1, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.98 g L-1 and 3.36 g L-1 respectively, and the sensibility obtained was 0.086 µA L g-1 mm-2. These results show that the multi-walled carbon nanotubes in water and Nafion® allow obtaining an anodic signal corresponding to the yeast, which facilitates its quantification through electrochemical methodologies, favoring the reduction of analysis times and costs compared with other techniques.

Thermoplastic electrodes as a new electrochemical platform coupled to microfluidic devices for tryptamine determination.

This study reports a new electrochemical method for tryptamine determination using a paper-based microfluidic device and a thermoplastic electrode (TPE) as an amperometric detector. Tryptamine (Tryp) is a biogenic amine present in drinks and foods. Even though this compound has some beneficial effects on human health, the ingestion of foods with high concentrations of Tryp may be detrimental, which justifies the need for monitoring the Tryp levels. The TPEs were made from 50% carbon black and 50% polycaprolactone and characterized by cyclic voltammetry, demonstrating enhancement in the analytical response compared to other carbon composites. TPEs also showed a better antifouling effect for Tryp compared to conventional glassy carbon electrodes. Once characterized, the electrodes were incorporated into the microfluidic device to determine Tryp in water and cheese samples using amperometry. A linear range was achieved from 10 to 75 µmol L-1 with limits of detection and quantification of 3.2 and 10.5 µmol L-1, respectively. Therefore, this work shows promising findings of the electrochemical determination of Tryp, bringing valuable results regarding the electrochemical properties of thermoplastic composites.

Evaluation of the Cadmium Accumulation in Tamarillo Cells (Solanum betaceum) by Indirect Electrochemical Detection of Cysteine-Rich Peptides.

Long-term cadmium intake can be very dangerous to human health due to its toxic effects. Although people can be contaminated with this element from different sources, contaminated food is probably the most important one. Foods such as vegetables and fruits can become contaminated with cadmium existing in soils, irrigation water, or chemical fertilizers. Some plants produce an excess of cysteine-rich peptides (CRp) when affected by high concentrations of heavy metals such as cadmium, thus indicating the presence of this type of contamination. Among these plants is tamarillo (Solanum betaceum), which is locally known as "tree tomato". This is a native plant widely consumed in the Ecuadorian Andes because of its abundance, low cost, and high content of vitamin C and fiber. The fact that Solanum betaceum produces CRp upon contamination with heavy metals means that this plant may be able to accumulate heavy metals. If this is the case, the plant can possibly be used as an indicator of metal pollution. The main goals of the present work were to evaluate the possibility of using Solanum betaceum as an indicator of metal contamination in plants and to examine its capability to accumulate metals. Both goals were met by determination of the amounts of CRp produced by Solanum betaceum cells cultivated in vitro in the laboratory under controlled conditions in the presence of different concentrations of cadmium. The CRp determination was carried out by means of electrogeneration of iodine in an iodide solution containing reduced glutathione as a biological thiol model. Solanum betaceum cells were grown in a Murashige and Skoog solution enriched with a 30 g L-1 sugar aqueous solution and 1 mg L-1 2,4-dichlorophenoxyacetic acid. The results of these experiments confirmed the following: (1) CRp production is a function of the amount of cadmium present as a contaminant up to a limiting value after which cell apoptosis occurs; (2) Solanum betaceum accumulates cadmium; (3) the analytical method used is appropriate for CRp determination; and (4) CRp determination is a valid alternative to detect contamination by heavy metals in plants.

Amperometric determination of myo-inositol by using a glassy carbon electrode modified with molecularly imprinted polypyrrole, reduced graphene oxide and nickel nanoparticles.

This paper reports on the development of an amperometric method for the determination of myo-inositol. The method involves coating of a glassy carbon electrode (GCE) with a molecularly imprinted polymer (MIP) and reduced graphene oxide (RGO) that was modified with nickel nanoparticles (NiNPs). The MIP was prepared by electropolymerization of pyrrole on the surface of the GCE in the presence of myo-inositol molecules. The construction steps of the modified electrode were monitored via cyclic voltammetry, atomic force microscopy, scanning electron microscopy and X-ray Photoelectron Spectroscopy. The results were evaluated using differential pulse voltammetry, in which hexacyanoferrate was used as an electrochemically active probe. Under optimized experimental conditions, the imprint-modified GCE has a linear response in the 1.0 × 10-10 mol L-1 to 1.0 × 10-8 mol L-1 concentration range, with a 7.6 × 10-11 mol L-1 detection limit and an electrochemical sensitivity of 4.5 µA·cm-2 µmol-1. The method showed improved selectivity even in the presence of molecules with similar chemical structure. The GCE modified was successfully applied to the determination of myo-inositol in sugarcane vinasse where it yielded recoveries that ranged from 95 to 102%. Graphical abstract Schematic presentation of molecularly imprinted polymer (MIP) on a glassy carbon electrode (GCE) modified with nickel nanoparticles (NiNP) anchored in reduced graphene oxide (RGO). The resulting MIP/NiNP/RGO-GCE was used for indirect determination of myo-inositol.