An amperometric sensor system based on acetylcholinesterase (AChE) was used for a paraoxon assay. Paraoxon-inhibited AChE resulted in the decrease of acetylthiocholine hydrolysis and the further oxidation of thiocholine on a platinum electrode. Thus described, the system allows for the detection of 1.2 ppb of paraoxon responding to absolute 12 pg. The sensor system functionality was verified on spiked beverages. The practical impact of system was summarized and future implementation is expected.