Fluorescence-based sensing of p-nitrophenol and p-nitrophenyl substituent organophosphates

Abstract

A novel detection method for organophosphate neurotoxins has been described, based on the fluorescence quenching of a Coumarin derivative. These dyes are similar in structure to some organophosphates (OPs), and they fluoresce in the blue–green region of the spectra. This methodology has been utilized for the detection of organophosphates whose hydrolysis product is p-nitrophenol by using an enzyme, organophosphorus hydrolase (OPH). Coumarin1 in the presence of p-nitrophenol results in a quenching of fluorescence, providing a direct measure of the concentration of p-nitrophenol present in the sample. The decrease in fluorescence intensity is proportional to the paraoxon concentration in the range of 7.0 × 10 −7–1.7 × 10 −4 M. The specificity of this sensing application for p-nitrophenyl substituent OPs has also been demonstrated. OPs are a class of synthetic organic pesticides which generally have a short residual life and can cause numerous acute and chronic health effects. They have been an integral part of the agricultural industry for the past several decades due to their target specificities and selectable toxicities. The toxic nature of these compounds can be attributed to the species–specific inhibition of acetylcholinesterase (AChE), an important enzyme responsible for the regeneration of neural synaptic function. In addition to their wide agricultural and urban usage, they have also been exploited for the development of neurological chemical warfare agents. Currently available technologies for OP detection include sol–gel thin films, screen printed electrodes, acoustic patterning, gas chromatography–mass spectrometry, and various other intricate techniques that have limited field applicabilities. This optically-based approach promises much simpler and more direct detection capabilities.