Highly Sensitive Detection of Organophosphorus Pesticides Represented by Methamidophos via Inner Filter Effect of Au Nanoparticles on the Fluorescence of CdTe Quantum Dots

A sensitive fluorescence detection method of organophosphate pesticides (OPs) represented by methamidophos was developed using the inner filter effect (IFE) of Au nanoparticles (AuNPs) on CdTe quantum dots (QDs). The fluorescence of CdTe QDs was remarkably quenched with the presence of AuNPs via IFE. Acetylcholinesterase (AChE) catalyzed the hydrolysis of acetylthiocholine into thiocholine, which could induce the aggregation of AuNPs and decrease their characteristic absorption, making IFE-decreased fluorescence of CdTe QDs recovered. OPs can inhibit the activity of AChE, thus preventing the aggregation of AuNPs and the fluorescence recovery of CdTe QDs. Therefore, the IFE of fluorescence between AuNPs and CdTe QDs could convert the absorption signal to fluorescence signal, which improved the detection sensitivity of OPs in vegetables. Under the optimum conditions, the response was linearly proportional to the concentration of methamidophos in the range of 0.06 similar to 0.78 mg/kg with a detection limit of 2 mu g/kg (3 sigma) which was superior to the method of GB/T 5009.199-2003. The proposed assay exhibited good reproducibility and accuracy, providing a simple and rapid method for the screening of OPs.