Indicator-catalyst displacement assay for tandem detection and signal amplification of dimethoate organophosphate pesticide

This paper describes the chemosensing and catalytic amplification properties of [Mn^III(TPP)(NCS)]–[Pd^II(DMSO)Cl₂] (1, TPP = 5,10,15,20-tetraphenyl-21H,23H-porphine) for detecting the organophosphate pesticide dimethoate. Complex 1 selectively detects dimethoate, resulting in a visual color change from yellowish-brown to green with a UV–vis spectroscopic method detection limit (MDL) of 22.7 μM. This selectivity is attributed to the formation of a more stable Pd^II(dimethoate)₂Cl₂ adduct, resulting in the release of the colored Mn^III(TPP)(NCS) unit from complex 1. Interestingly, the free Pd^II(dimethoate)₂Cl₂ released acts as a catalyst for the Heck coupling reaction of 5-diethylamino-2-iodo-phenyl ester (2), producing the highly fluorescent 7-diethylaminocoumarin (3). This catalytic process results in significant signal amplification, enhancing the original sensitivity by 25 times, with a spectrofluorimetric MDL of 0.9 μM. The proposed indicator-catalyst displacement assay successfully quantifies dimethoate concentrations in natural water samples, exhibiting good recoveries (92.5–108.1%) and low relative standard deviations (1.2–6.2%). Copyright © 2024 Elsevier B.V. All rights reserved.