Abstract
Since World War II, the use of pesticides has increased to not only reduce the agricultural labor but also increase productivity. However, the residual neurotoxic pesticides, such as organophosphorous or carbamate pesticides, in foods has become a major public health issue with a high degree of attention. Accordingly, the development and validation of a rapid, simple, and inexpensive method for screening analysis of the residual pesticides in foods has attracted wide attention. However, most of the currently reported screening methods are costly, time consuming, and inconvenient, especially for the in-situ test. Therefore, a rapid, in situ, inexpensive and simple method for screening the residual pesticides in foods and drinking water is still highly demanded. Because the presence of thiocholine can cause the aggregation of gold nanoparticles (AuNPs) due to the electrostatic and gold-thiol interaction, which can result in a red-shift of the plasmon absorption. In addition to the aggregation of AuNPs, thiocholine can also cause the release of rhodamine B (RB) from the surface of AuNPs. To establish a series of AuNPs-based optical screening analytical methods, an enzymatic inhibition reaction coupling to the gold nanoparticles-based colorimetric and fluorometric detections were developed to determine several neurotoxic organophosphorous (OPPs) and carbamate pesticides. To induce the aggregation of AuNPs and the release of RB from RB-AuNPs, in this study, thiocholine was formed based on the hydrolysis reaction of acetylthiocholine (AtCH) catalyzed by the enzyme, acetylcholinesterase (AChE). Meanwhile, because both OPPs and carbamate can inhibit the activity of AChE, the existence of pesticide residues described above was found can slow down and even prevent the aggregation of AuNPs. On the basis of this reaction mechanism, various analytical schemes were designed to detect OPPs and carbamate pesticides by the color change with naked eye (visual inspection), UV/Vis spectrophotometric measurement, or by the change in fluorescence intensity with fluorometric measurement. Based on the experimental results, our developed screening methods were found applicable to detect the maximum residual concentrations of six pesticides in tap water and vegetables.