Rapid detection of pyraclostrobin fungicide residues in lemon with surface-enhanced Raman spectroscopy

Abstract

Pyraclostrobin (methyl N-(2-{[1-(4-chlorophenyl)-1 H-pyrazol-3-yl]oxymethyl}phenyl) N-methoxycarbamate) is a synthetic fungicide used against a wide range of plant pathogens. Its mode of action/mechanisms of toxicity is the inhibition of mitochondrial respiration of fungi. Given the extended application of pyraclostrobin in the agricultural sector, and its potential hazard for humans, it is necessary to monitor its residual traces in agricultural products to ensure food safety. This work reports the first application of surface-enhanced Raman spectroscopy (SERS) for qualitative and semi-quantitative detections of the fungicide both in standard solutions and in lemon peel extractions from contaminated samples at laboratory scale. For this, a simple, low-cost and easy-to-construct SERS active substrate consisting of a ring of silver nanoparticles (AgNPs) immobilized on a glass slide was used. Pyraclostrobin up to 6 × 10− 5 M concentration on the lemon peel was detected in a fast and neat procedure. The adsorption mechanism of the pesticide on the AgNPs was characterized by comparison between the normal Raman and SERS spectra of the substance and by quantum-chemical calculations of different pyraclostrobin-Ag3 complexes. Theoretical predictions and experimental data suggest that the molecule is able to adopt different orientations on the substrate.