Electrochemical determination of Diuron in Brazilian crops: f-MWCNT@Chi-AgNPs nanocomposite-modified screen-printed electrode for food safety monitoring

In this study, an inexpensive, easy-to-make screen-printed electrochemical (SPE) sensor was developed and applied for diuron (DIU) detection in Brazilian crops. The SPE was modified with a hybrid nanocomposite, which consisted of functionalized carbon nanotubes, chitosan and silver nanoparticles (f-MWCNT@Chi-AgNPs). The AgNPs were obtained through a simple and rapid green synthesis using lemon leaf extract as a reducing agent. The sensor exhibits irreversible electrochemical behavior with a diffusion-controlled response. The SPE-modified sensor when applied for DIU detection, was obtained a wide linear range (0.02–50.0 μM), a low LOD (0.005 μM), and a high sensitivity. Experimental variables, such as pH and scan rate were optimized, with pH 7.0 identified as the optimal medium. The modified SPE sensor demonstrated excellent selectivity against common interferents, operational stability, and no memory effect. The DFT analysis, from the M06-2X and B3LYP functionals, and the Def2-SVP basis set, reveals that the DIU molecule is a moderate electrophile. These data suggest the SPE/f-MWCNT@Chi-AgNPs are both highly reactive and stable for DIU oxidation. Its practical applicability was confirmed through the analysis of real samples (orange fruit, orange juice, tangerine, sugarcane and tomato), where recovery rates between 100.09 and 110.61 % were obtained, with RSD below 4.0 %. The combination of conductive materials with porous structure and sustainable synthesis yielded an efficient analytical platform. The proposed sensor can be employed as a viable, rapid and effective alternative tool for monitoring pesticide residues in complex matrices, with strong potential for application in environmental and food quality analysis.