Theoretical and experimental findings regarding the electroanalysis of dienestrol in natural waters using a silver nanoparticles/single-walled carbon nanotubes-based amperometric sensor

Aware of the irreparable damage that synthetic estrogens can trigger in the environment, the search for analytical methods capable of mapping the sources, levels and fate of these micropollutants is a subject that demands enormous scientific effort. The present work follows this trend, reporting a silver nanoparticles/single-walled carbon nanotubes-based composite electrode (AgNP/SWCNT-CPE) that has multiple functionalities for dienestrol (DNL) electroanalysis. Theoretical and experimental data indicate that DNL reactivity on AgNP/SWCNT-CPE is more critical under acidic conditions, favoring its irreversible oxidation to quinone derivatives. The reaction kinetics is limited by interfacial adsorption events, whose intensity of the molecule-surface interaction depends on variables such as Gibbs free energy, ionization potential, HOMO-LUMO gap, and dipole moment. Since the silver‑carbon heterojunction has low overpotential towards the oxygen evolution reaction, it is speculated that AgNP/SWCNT-CPE is more resistant to surface fouling due to the formation of chemisorbed radicals on its electroactive area. Based on the detection limit (43.7 nmol L−1 DNL), the analytical performance of the proposed method is equivalent to those attained by chemiluminescence, electrophoresis, chromatography and electrochemistry. Given the sensitivity obtained, AgNP/SWCNT-CPE was successfully used to quantify DNL in river waters containing different levels of organic matter, without compromising the accuracy, stability and robustness of the amperometric measurements, reiterating the reliability and feasibility of this proposal.