Antioxidants are synthetic or natural compounds capable of preventing or delaying oxidative damage caused by chemical species that can oxidize cell biomolecules, such as proteins, membranes, and DNA, leading to the development of various pathologies, such as cancer, atherosclerosis, Parkinson, Alzheimer, and other diseases serious. In this study, an amperometric biosensor was used to determine the antioxidant activity of teas and effervescent products based on vitamin C, available on the market. A sensor composed of three electrodes was used. The performance of the following electrochemical mediators was evaluated: meldola blue combined with Reineck salt (MBRS), Prussian blue (PB), and cobalt phthalocyanine (CoPC), as well as the time of polymerization in the enzymatic immobilization process and the agitation process during chronoamperometric measurements. Prussian blue proved to be more efficient as a mediator for the desired purposes. After optimizing the construction stages of the biosensor, as well as the operational parameters, it presented stability for a period of 7 months. The results clearly indicate that the biosensor can be successfully used to detect fraud in products called “antioxidants” or even in drugs containing less ascorbic acid than indicated on the labels. The detection limit was set at 4.93 µmol·L−1.

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In this work, we have proposed an electrochemical sensor for the detection of pesticides by using a ceramic composite with a SiO2 surface modified with Sm2O3 nanoparticles and C‐graphite (SSMG), obtained by the sol‐gel process and immobilized by adsorption in Meldola Blue cationic dye (MB). The composite was called (SSMG/MB), which was characterized by spectroscopic, electrochemical techniques, Fourier‐transform infrared spectroscopy, and Cyclic Voltammetry. The proposed sensor was applied for the glyphosate electrochemical detection, using Differential Pulse Voltammetry, and, under optimized parameters has presented the linear response for the pesticide in the concentration range from 0.99 to 7.94 (μmol L−1; R2=0.9963; n=8). The calculated values for the detection limit and the quantification limit were 0.15 and 0.49 μmol L−1, respectively. Therefore, the new electrochemical sensor based on SiO2, NPsSm2O3, C‐graphite, and MB hybrid material was developed for the first time for glyphosate determination, which has demonstrated high potential for the development of new hybrid devices for environmental control.

The objective of this study was to conduct chemical analyses of bioactive compounds found in the bark and leaves of Humiria balsamifera (Aubl.) A. St. Hil. and Hymenaea courbaril L. These species are found in the transitional zones between the Amazon and Cerrado Maranhense. Chemical screening was performed to detect the presence of phenols, tannins, anthocyanins, anthocyanidins, leucoanthocyanidins and other secondary metabolites. Quantification of the concentrations of phenolic compounds, anthocyanins, flavonoids, and antioxidants was performed by ultraviolet spectrophotometry through recommended methodologies. Extracts of the leaves of Humiria balsamifera (Aubl.) A. St. Hil. were found to have high concentrations of flobabénic tannins. Tannins, flavonoids, flavonols, flavonones, flavanonols, xanthones, steroids, and saponins were also found in bark extracts of the same species. The levels of phenolic compounds, anthocyanins, and flavonoids in the bark of Humiria balsamifera (Aubl.) A. St. Hil. were higher than those measured in the leaves, reflecting that the leaves greater capacity to sequester free radicals. For Hymenaea courbaril L., the main bioactive compounds found in this study were flavonones, phenols, and catechins. The plant species Humiria balsamifera (Aubl.) A. St. Hil. and Hymenaea courbaril L. showed potential for antioxidant activity and for use in the pharmacological and food industries.

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