Colorimetric and visual determination of total nereistoxin-related insecticides by exploiting a nereistoxin-driven aggregation of gold nanoparticles

We describe a method for the visual and colorimetric determination of total nereistoxin-related insecticide residues. It is based on the nereistoxin-induced aggregation of gold nanoparticles (AuNPs). The nereistoxin-related insecticides are first converted to nereistoxins in a pretreatment step that involves liquid-liquid extraction and hydrolysis for sample clean-up. Next, the interaction between nereistoxins and AuNPs provides a possibility to visually semi-quantify or accurately quantify nereistoxins because it is associated with a color change from red to blue. The interaction between nereistoxins and AuNPs is caused by the electrostatic interactions and the strong Au-S covalent bonds. The photometric assay is performed by measuring the ratio of absorbances at 660 and 519 nm, respectively. It has a detection range from 50 to 250 mu g kg(-1) and a detection limit of 40 mu g kg(-1) to for the total quantity of nereistoxin-related insecticides. The visually detectable color change to blue occurs in the 50 to 100 mu g kg(-1) concentration range, and this enables a fast visual test on whether or not the concentration of total nereistoxin-related insecticides exceeds the tolerated level of 100 mu g kg(-1). The method was applied to the analysis of nereistoxin-related insecticides in agricultural products.