Spectrophotometric Detection of Dimethyl Methyl-Phosphonate Using Plant-Esterase

We have developed an optical detection method for dimethyl methyl-phosphonate (DMMP) based on reversible inhibition of plant-esterase by monosulfonate tetraphenyl porphyrin (TPPSi). The abosorbance spectrum of the porphyrin-enzyme complex solution is measured with a LAMBDA 500 spectrophotometer. The characteristics of the abosorbance spectrum of TPPSi are specific and different when the porphyrin is bound to the enzyme. Addition of alpha-naphthyl acetate or DMMP displaces the porphyrin from the enzyme resulting in reduced absorbance intensity at 420 nm. Absorbance changes at 420 nm show linear dependence on DMMP concentration. DMMP concentrations as low as 9times10^-11mol L^-1 have been detected. This optically-based approach promised much simpler and more sensitive detection capabilities.