A facile and highly sensitive signaling strategy for organophosphorus compounds (OPs) based on acetylcholinesterase (AChE)–acetylthiocholine (ATCh) catalytic reaction and II–VI group photoluminescent CdTe quantum dots (QDs) prepared from low molar ratio of thiols to Cd²⁺ has been developed. Photoluminescence (PL) of the ensemble system can be modulated by the enzyme catalytic reaction and OPs, as the resulting catalytic product, namely thiolcholine (TCh) and H⁺, can significantly decrease PL of the prepared QDs, while OPs can inhibit this AChE–ATCh catalytic reaction. This signaling platform shows much more enhanced sensitivity to highly toxic OPs such as nerve agents and organophosphate pesticides, compared with previous reports.