Multi-Walled Carbon Nanotube-Modified Carbon Paste Electrode for Fipronil Detection in Environmental Samples

Fipronil (FIP) is a pesticide widely used for controlling soil pests and preventing parasitic infestations in dogs. However, its widespread and often indiscriminate application has led to contamination of aquatic environments in several countries, including Brazil, highlighting the need for new methodologies to detect its residues in food and the environment. This study aimed to develop a nanostructured carbon paste sensor using multi-walled carbon nanotubes (MWCNTs) to detect FIP. Deposition of nanomaterials, such as MWCNTs, into electrochemical sensors can significantly enhance their performance. Their unique attributes, including a high surface-to-volume ratio and excellent electrical conductivity, are key to this improvement. The carbon paste electrode was modified with 20% w/w MWCNT, demonstrating the best electrochemical response as confirmed by cyclic voltammetry. Square wave voltammetry enabled the detection of FIP with a limit of detection of 0.377 µmol L⁻¹ and a limit of quantification of 1.26 µmol L⁻¹. Interference studies were conducted using potential interferents, including Atrazine, NaCl, KCl, CaCl₂, FeCl₃, and ZnCl₂, yielding a relative standard deviation of around 6%. Additionally, the sensor stability was evaluated over 22 days, showing only a 2.6% reduction in the peak current. This sensor was successfully used to detect FIP in tap water samples with good recoveries of 101.8–104%. Thus, the use of MWCNTs proved highly promising for developing electrochemical sensors for FIP detection due to their hydrophobic nature, which facilitates the adsorption of FIP molecules onto the electrode surface.