A sensitive enzymatic method for paraoxon detection based on enzyme inhibition and fluorescence quenching

A sensitive and selective method for the paraoxon detection based on enzyme inhibition and fluorescence quenching was presented in this study. Under the catalytic effect of acetylcholinesterase (AChE), acetylthiocholine (ATCh) hydrolysis released thiocholine (TCh) which could react with N-(7-dimethylamino-4-methylcoumarin-3-yl) maleimide (DACM) to produce a blue fluorescence compound. Subsequently, AChE catalytic activity was inhibited with the addition of paraoxon, which caused TCh decreased, leading to a significant decrease of the blue fluorescent compound. Meanwhile, p-nitrophenol, the hydrolysis product of paraoxon, would lead to a quenching of the fluorescence. Therefore, fluorescence intensity of the system would decrease dramatically by a combined effect of enzyme inhibition and fluorescence quenching. Under optimal experimental conditions, an excellent linear relationship between the decrease of fluorescence intensity and paraoxon concentration over the range from 5.5 × 10−12 to 1.8 × 10−10 mol L−1 was obtained. Fluorescence background caused by nonenzymatic hydrolysis of ATCh or other matters was relatively low, the proposed approach offered adequate sensitivity for the detection of paraoxon at 3.5 × 10−12 mol L−1.