Fluorometric microplate-based dimethoate assay using CdSe/ZnS quantum dots coated with a molecularly imprinted polymer

A microplate-based assay is described for the sensitive and selective fluorometric determination of the pesticide dimethoate. Molecularly imprinted polymer (MIP)-coated CdSe/ZnS quantum dots (QDs) are used as the molecular recognition probe. The MIP-coated QDs were synthesized using one-step reversed-phase microemulsion in the presence of hydrophobic CdSe/ZnS QDs. Copolymerization was performed by using 3-aminopropyltriethoxysilane as the functional monomer, tetraethoxysilane as the cross-linker, and dimethoate as the template. The fluorescence of the coated QDs is quenched by dimethoate when dimethoate becomes rebound on the imprinting sites of the MIP. Under the optimal conditions, fluorescence (best measured at excitation/emisison wavelengths of 380/620 nm) drops linearly in the 5.0–150 μg L−1 dimethoate concentration range, and the limit of detection is 2.1 μg L−1 (at S/N = 3). The assay was utilized for dimethoate determination in spiked real samples. Satisfactory recoveries (89.8%–98.0%) with relatively standard deviations of <4.9% are obtained. The method is rapid, cost-effective, sensitive, and selective. The use of microplate allows for the quantitation of a large number of samples simultaneously.