Organophosphate hydrolase conjugated UiO-66-NH2 MOF based highly sensitive optical detection of methyl parathion

Abstract

The hexahistidine-tagged organophosphorus hydrolase (OPH^6His) has been immobilized on a Zr-MOF, namely UiO-66-NH₂. The resulting enzyme-MOF composite was used as a carrier to facilitate the hydrolysis of an organophosphate pesticide, i.e., methyl parathion in to p-nitrophenol (PNP). The formation of PNP took place in direct proportion to the added pesticide concentration. Coumarin1 (7-diethylamino-4-methylcoumarin) was then introduced in the reaction mixture as a reporter fluorescent molecule. As PNP acted to quench the fluorescence of coumarin1, it became possible to detect methyl parathion over a wide concentration range of 10-10⁶ ng/mL with an achievable limit of quantification as 10 ng/mL. The immobilization of OPH^6His on the surface of UiO-66-NH₂ was found to endow an improvement in the enzymatic activity by about 37%. The OPH^6His/UiO-66-NH₂ conjugate was reusable for at least up to eight times and also found stable toward long-term storage (minimum 60 days). The potential practical utility of the above proposed sensing method has been demonstrated by employing it for an accurate analysis of pesticide-spiked food samples.

Keywords: Bioconjugate; Biosensing; Enzyme activity; Organophosphate hydrolase; Pesticide; Zr-MOF.