Quantitative Analysis of Methyl-Parathion Pesticide in Presence of Enzyme Substrate Using Tapered Fiber Optic Biosensor

Application of a non-adiabatic tapered fiber optic biosensor for real-time, label-free detection of methylparathion pesticide (MPT) in presence of acetylthiocholine iodide (ATCh) is presented. The limit of detection of MPT in the presence of 1 mM ATCh as an enzyme substrate is found to be as low as 23x10(-9) M (S/N=3). The proposed sensor shows a dynamic range of 2.3 nm and a working range of 0.12 to 31 mu M. More importantly, it has the capability of quantifying the binding constants of MPT to the enzyme acetylcholinesterase (AChE) by performing just a single experiment. This can be done through the kinetic analysis of the analyte-enzyme reaction in the presence/absence of ATCh. The results show an association rate of 3.835x10 4 M-1s(-1) and a dissociation rate of 0.2745 s(-1) for MPT-AChE binding in presence of ATCh which lead to a value of 1.4x10 (5) M-1 for equilibrium binding constant and 7.16 mu M for dissociation constant. Detection of MPT in the tap and river water at low levels has been achieved and the sensor specificity examined against different substances. Based on the obtained results, our biosensor can pave the way toward low-cost, real-time, label-free, and quantitative determination of organophosphate pesticides in real samples.