Hydrolyzed Product Mediated Aggregation of l-Cysteine-Modified Gold Nanoparticles as a Colorimetric Probe for Carbamate Residues in Chilis

Abstract

A sensitive colorimetric assay is reported for carbamate pesticide detection. The detection strategy was based on carbamate hydrolyzed product induced aggregation of l-cysteine-modified gold nanoparticles (Cys-AuNPs) in the presence of pH 5.8 phosphate buffer and sodium chloride. Sodium chloride was added to increase the speed of aggregation (pre-aggregation) to make the modified gold particles less stable. Carbamate pesticides are easily hydrolyzed at room temperature in the presence of sodium hydroxide. Their hydrolyzed products contain constituents that can easily reduce the Cys-AuNP aggregation, with concomitant color perturbation from ruby red to purple and blue-gray in 10 min. The linear range of the determination of carbaryl and methomyl was from 14.0 to 71.0 µg/mL and 7.0 to 36.0 µg/mL, respectively, with limits of detection of 7.15 µg/mL for carbaryl and 3.49 µg/mL for methomyl. The assay’s practicality was demonstrated by the determination of chili samples with satisfactory recovery (87–91%) and precision (relative standard deviations less than 3.5%). Thus, the assay is a promising screening tool of pesticide residues in chili with high selectivity.