Amino acid modified graphene oxide for the simultaneous capture and electrochemical detection of glyphosate

Amino acid modified graphene oxide derivatives (GO-AA) are herein proposed as active materials for the capture and consequent electrochemical detection of organic pollutants in aqueous media. Glyphosate (GLY), an herbicide present in many water compartments, was chosen as benchmark species to test the effectiveness of these materials for its electroactive nature, allowing direct evidence of the capture event. L-Lysine, L-Arginine or LMethionine were grafted on GO surface through epoxide ring opening reaction, promoting the amino acids binding and the concomitant partial reduction of GO. The synthetic process results in a charge resistance drop from 8.1 KΩ for GO to 0.8–2.1 KΩ for the various GO-AA, supporting the applicability of these materials in electrochemical sensing. The resulting GO-Lysine, GO-Arginine and GO-Methionine were exploited for GLY adsorption from water. GO-Lysine was found to have the strongest interaction with GLY, with a removal efficiency of 76 % after 1 h, which is about two-fold higher than those of granular activated carbon, the industrial benchmark adsorbent. GO-AAs outperform the pristine unmodified material also when exploited as active materials for the capturing and following electrochemical detection of GLY. GO-Lysine showed the best sensitivity and allowed the recognition of GLY in water even when present at concentration levels down to 2 μg/L. Molecular dynamics simulations confirmed that the enhanced performance of this material can be ascribed to the hydrogen bond and salt bridge interactions between Lys moieties and GLY, originated from hydrogen bond and salt bridge interactions.