Determination of Organophosphorus Pesticides in Fortified Tomatoes by Fluorescence Quenching of Cadmium Selenium – Zinc Sulfide Quantum Dots

Quantum dots (QDs) have attracted great interest in fluorescence sensing. However, due to the surface passivation of QDs, it is still challenging to develop a sensing method based on the direct use of QD without the involvement of molecular recognition receptors. In this work, a very simple but practical strategy for highly passivated commercial CdSe/ZnS core-shell QDs is proposed to directly determine phosphorothiolate pesticides. This strategy is based on the fact that thiophosphorus hydrolyzates, formed in the alkaline hydrolysis of phosphorothiolates, strongly quench the fluorescence emission of the QDs by an electron transfer mechanism. The design is very easy to implement, requiring only the addition of the analyte into the quantum dot solution at room temperature. The 'light-off' response shows a wide linear range from 0.0001 to 160 mu g mL(-1) with a detection limit of approximately 0.0967 ng mL(-1) (0.00012 mg kg(-1)), which is considerably lower than the maximum residue limit of 0.01 mg kg(-1) allowed by the European Union. More importantly, ethion may be determined directly in fortified tomatoes by this protocol, demonstrating potential broad applications in food quality control.