Colorimetric assay for visual determination of imidacloprid in water and fruit samples using asparagine modified gold nanoparticles

High precision and rapid detection of pesticides are one of the most imperative requirements today to overcome environmental and food safety problems. Therefore, here, in this study, we proposed a simple colorimetric sensor for the visual determination of imidacloprid (IMD) using asparagine (Asp)-modified AuNPs. The synthesized Asp-AuNPs were characterized using UV–visible spectroscopy, TEM, FTIR and DLS techniques. The colorimetric detection strategy was based on the significant red-shift in the absorption spectra of Asp-AuNPs (524 nm) to 656 nm with the addition of IMD. The electron-rich (NH 2 ) group on surfaces of Asp-AuNPs act as an excellent colorimetric probe, which induced the aggregation of Asp-AuNPs in the presence of IMD, resulting in a visual colour change of Asp-AuNPs from wine-red to purple-blue. Under optimized conditions, the linear graph was plotted between the absorption ratio at A 524 /A 656 and imidacloprid concentration in the range of 10–1000 µM. The detection limit was found to be 1.09 µM. The Asp-AuNPs showed a good response for visual detection of IMD in the presence of other common interfering pesticides and metal ions. Furthermore, to assess the applicability of the proposed method, real (tap and drinking) water and apple samples were analysed using Asp-AuNPs, the obtained findings demonstrated that the devised method has great potential for the determination of IMD in real samples.