Multi-walled carbon nanotube-modified screen-printed sensor for ultrasensitive fipronil determination in river water

The extensive use of fipronil (FIP), a phenylpyrazole insecticide, has generated increasing environmental concern due to its persistence, bioaccumulation, and toxicity to non-target organisms. To enable rapid and reliable monitoring of this contaminant, a screen-printed electrochemical sensor modified with multi-walled carbon nanotubes (SPE/MWCNT) was developed for the ultrasensitive determination of FIP. The incorporation of MWCNTs enhanced the electrode’s electroactive surface area (0.177 cm2 vs. 0.120 cm2 for the unmodified SPE), reduced the peak-to-peak separation (ΔEp) from 180 to 130 mV, and doubled the redox current, confirming improved electron-transfer kinetics. Under optimized conditions (Britton-Robinson buffer, pH 10), the sensor exhibited a detection limit of 0.0046 µmol L–1 and a quantification limit of 0.015 µmol L–1 using differential-pulse voltammetry. Importantly, the sensor’s performance was further validated in real environmental samples collected from the Guandu River (Rio de Janeiro, Brazil), achieving a LOD of 0.0086 µmol L–1 and the LOQ was 0.0285 µmol L–1. Recovery rates ranged from 93.6% to 102% for tap water, 99.6% to 107.3% for apple juice, and 93.3% to 112.2% for eggshell samples, with operational stability maintained for 42 days. The device also demonstrated high selectivity in the presence of common ionic and organic interferents, including atrazine and chlorpyrifos. These findings indicate that the SPE/MWCNT sensor is portable, cost-effective, and analytically robust, supporting on-site determination of pesticides in complex water matrices. This technology provides a valuable tool for environmental surveillance and early-warning systems addressing pesticide contamination.