Biochar: An environmentally friendly platform for construction of a SARS-CoV-2 electrochemical immunosensor.

Waste management is a key feature to ensure sustainable consumption and production patterns, and to combat the impacts of climate change. In this scenario, the production of biochar from different biomasses results in environmental and economic advantages. In this study, biochar was produced from sugarcane bagasse pyrolysis, to immobilize biomolecules, in order to assemble an electrochemical immunosensor to detect antibodies against SARS-CoV-2. For this, screen-printed carbon electrodes (SPCE) were modified with a dispersion of biochar and used to immobilize the receptor-binding-domain (RBD) against virus S-protein, through EDC/NHS crosslinking reaction. Under the best set of experimental conditions, negative and positive serum samples responses distinguished based on a cutoff value of 82.3 %, at a 95 % confidence level. The immunosensor showed selective behavior to antibodies against yellow fever and its performance was stable up to 7 days of storage. Therefore, biochar yielded from sugarcane bagasse is an ecofriendly material that can be used as a platform to immobilize biomolecules for construction of electrochemical biosensors.

Development and validation of voltammetric method for determination of amoxicillin in river water.

Amoxicillin is an antibiotic that can accumulate in aquatic environments and lead to the development of resistant bacteria; thus, its determination is of great importance. In this study, a glassy carbon electrode modified with reduced graphene oxide and Nafion was used as a sensor in a square-wave voltammetry method for determination of amoxicillin in river water samples from Guarapuava city, Brazil. The method was validated, using parameters and statistical tools recommended by the validation guidelines, in the range of 1.8-5.4 µmol L-1 (r = 0.922 and R2 = 85.1%). The analytical curve was constructed using external standard calibration in pure electrolyte, since the matrix effect was not significant. Results of linear regression analysis, lack of fit test and analysis of the residual plots pointed that the linear regression was significant, without lack of fit of linear model and that the variances had homoscedastic distribution. Both coefficients of regression curve were significant and, thus, they were included in the regression equation: Response = 7.0 + 3.5CAMX. The limits of detection and quantification were 0.36 and 1.2 µmol L-1, respectively. The method was selective towards interferents such as humic acids and benzylpenicillin. The relative standard deviations for repeatability and intermediate precision were adequate according to the limits established in literature. The mean recoveries were statistically equal to those obtained through a comparative chromatography method, so, the accuracy of the method was also adequate. Therefore, the method can be applied to the voltammetric determination of amoxicillin in river water, affording reliable and consistent measurements.