Comparison of the performance analytical of two glyphosate electrochemical screening methods based on peroxidase enzyme inhibition

Silvina V.Kergaravat^a,b, Silvia N.Fabiano^a, Adriana R.Soutullo^c, Silvia R.Hernández^a

Laboratorio de Sensores y Biosensores, Facultad de Bioquímica y Ciencias Biológicas, UNL-CONICET, CCT Santa Fe, 3000 Santa Fe, Argentina.

Abstract

Glyphosate is the most widely used herbicide in Argentina. The information about this herbicide is controversial as some organisms classify it as dangerous and others as safety. Moreover, the world regulations are very different depending on country. However, many studies had reported its presence in numerous sample types, and also, had demonstrated adverse effects on environmental and human health. In the present work, two electrochemical screening methods based on horseradish peroxidase (HRP) inhibition have been developed for the glyphosate detection. In one of them, the working electrode was built in our laboratory with a graphite-epoxy compound mixture (GEC-E). While the other is based on a biosensor built with commercial screen-printed electrodes (SPE), for which on the working electrode, the HRP enzyme was immobilized by using the affinity reaction between streptavidin and biotin-peroxidase. The detection electrochemical technique was square-wave voltammetry (SWV). When glyphosate inhibits the activity of the soluble or immobilized enzyme, a decrease in the signal is generated at the electrode or biosensor, respectively, and this decrease is proportional to the amount of glyphosate in the sample. The linear range obtained was from 0.16 to 500 ng L^-1 glyphosate (R² = 0.9727) for the soluble HRP-based inhibition method with a limit of detection (LOD) of 0.085 ng L^-1. While the range was from 0.08 to 11 μg L^-1 glyphosate (R² = 0.9799) for immobilized HRP-based inhibition method with a LOD of 45 ng L^-1. For the screening detection of glyphosate, the decision limits (CCα) and detection capabilities (CCβ) were 115 and 130 ng L^-1 for the soluble HRP-based inhibition method and 111 and 122 ng L^-1 for biosensor, respectively. Recoveries from 71% to 96% and from 79% to 120% were obtained by two electrochemical methods from groundwater and superficial water with high organic matters spiked with glyphosate, respectively. Therefore, both electrochemical methods allow determining the glyphosate concentration at trace levels in accordance with the strictest European Parliament regulation (100 ng L^-1). The soluble HRP-based inhibition method shown better performance than biosensor, but the latter due to its simplicity, stability and portability could be used in the field monitoring or detection of this herbicide in the exposed areas.

Keywords: Glyphosate, Electrochemical, Biosensor, Enzyme-inhibition, Horseradish peroxidase.