The prevalently used immunoassays for fast screening of aftatoxins (AFs) usually cannot meet the requirement for simultaneous determination of total AFs (aflatoxin B1 + aflatoxin B2 + aflatoxin G1 + aflatoxin G2) due to the deficiency of highly group-specific antibodies. This paper describes a two-step chromogenic reaction based method to quantitatively detect total AFs in rice using colorimetric measurement without antibody. In the method, colorless AFs transform into green-colored indophenol products through the reaction with sodium hydroxide and 2,6-dibromoquinone-4-chloroimide (DBQC) successively, allowing selectively determining total AFs up to 3.9 μg/kg over other competitive mycotoxins under optimal conditions by a UV-vis spectrophotometer. In addition, the colorimetric measurement results of the rice samples agree well with that of a standard HPLC method, demonstrating the good reliability and applicability of the method. Uniquely, the method has potential for on-site detection of total AFs in rice when using a nylon membrane-based device.
A method is described for the determination of the pesticide chlorothalonil (CLT). It is based on the finding that citrate-capped gold nanoparticles (AuNPs) undergo aggregation on exposure to chlorothalonil. This is accompanied by a visually detectable color change from wine red to blue. The effect is due to the interaction of the cyano group of chlorothalonil with gold nanoparticles. The assay may also be performed by using a spectrometer. The ratio of absorbances at 700 nm and 520 nm (A/A) linearly drops in the 5 to 100 ng·mL CLT concentration range, with a 3.6 ng·mL detection limit. This is below the Chinese guideline value for cucumber. The method is rather simple and does not require any modification of the AuNPs or the utilization of antibody. It was successfully applied to the determination of CLT in (spiked) cucumber samples. Recoveries ranged from 80.4 to 97.4%, and the analytical results compared well with those obtained by HPLC. Graphical abstract Schematic of the assay. The strong interaction of the cyano group of acetamiprid with gold nanoparticles (AuNPs) via Au-N bond induces the aggregation of gold nanoparticles, and this is accompanied by a color change from red to purple.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.