Surface imprinted CoZn-bimetalic MOFs as selective colorimetric probe: Application for detection of dimethoate

Designing simple and selective sensors for on-site recognition of organophosphate toxins (OPs) is of great importance. Here, molecularly imprinted polymer (MIP)-capped CoZn bimetal imidazolate framework (CoZn ZIF) has been introduced as a specific probe for the quantification of dimethoate. The detection is based on its diminishing effect on the catalytic action of ZIF in 3,3′,5,5′-Tetramethylbenzidine (TMB)-hydrogen peroxide (H2O2) reaction. CoZn ZIF catalyzes the dissociation of H2O2 to hydroxyl radicals, which can then oxidize TMB and create a blue colored product. It was demonstrated that the catalytic performance of bimetal metal organic framework (MOF) is higher than that of single metal MOF of Co (ZIF-67) or Zn (ZIF-8). On the other hand, adsorbing dimethoate in the specific MIP sites on the surface of CoZn ZIF declines its catalytic action. This effect was exploited to design a selective colorimetric assay for dimethoate determination in fruit and wastewater samples. The decrease in the absorption intensity of final solution was proportional to the dimethoate concentration in the range of 0.02–1.2 μM, with a detection limit of 5.6 nM. The high specificity of MIP technique and great catalytic activity of CoZn ZIF, as well as the simplicity of colorimetric method led to a reliable screening assay.