Considering inter- or intra-individual variation in the normal levels of acetylcholinesterase (AChE), real-time measurement of AChE via the reactivation from a postexposure sample was used, and thus a baseline-free and reliable approach was proposed for detecting/screening low-dose organophosphorus pesticides (OPs) poisons. The principle of this technology is on the basis of parallel measurements of AChE activity before and after reactivation from a postexposure to simultaneously provide the content of dual biomarkers of both enzyme inhibition and enzyme adducts. It is more accurate and reliable compared with only one biomarker (inhibition or adduct). Reactivation from a postexposure sample is a better individual enzyme baseline compared to pre-exposure from the population average level in currently available approaches. AChE activity was measured with an electrochemical method. Greatly enhanced sensitivity was achieved by using Fe3O4/Au nanocomposites to enrich thiocholine, the hydrolysis product of active AChE, followed by electrochemical oxidative desorption of the adsorbed thiocholine. The validation of this method for measurement of OP exposures was further explored with in vitro paraoxon inhibited human red blood cells (RBCs) samples and demonstrated its practicability.