Carbon quantum dots (CQDs) obtained from natural organics attract significant attention due to the abundance of carbon sources, varieties of heteroatom doping (such as N, S, P) and good biocompatibility of precursor. In this study, tunable fluorescence emission CQDs originated from chlorophyll were synthesized and characterized. The fluorescence emission can be effectively quenched by gold nanoparticles (Au NPs) via fluorescence resonance energy transfer (FRET). Thiocholine, which was produced from acetylthiocholine (ATC) by the hydrolysis of butyrylcholinesterase (BChE), could cause the aggregation of Au NPs and the corresponding recovery of FRET-quenched fluorescence emission. The catalytic activity of BChE could be irreversibly inhibited by organophosphorus pesticides (OPs), thus, the recovery effect was reduced. By evaluating the fluorescence emission intensity of CQDs, a FRET-based sensing platform for OPs determination was established. Paraoxon was studied as an example of OPs. The sensing platform displayed a linear relationship with the logarithm of the paraoxon concentrations in the range of 0.05–50μgL−1 and the limit of detection (LOD) was 0.05μgL−1. Real sample study in tap and river water revealed that this sensing platform was repeatable and accurate. The results indicate that the OP sensor is promising for applications in food safety and environmental monitoring. •Tunable fluorescence emission of CQDs were synthesized and characterized.•The fluorescence emission of CQDs could be effectively quenched by Au NPs via FRET.•The quenched fluorescence emission of CQDs could be recovered by thiocholine.•A facile FRET-sensing platform for OPs determination was established.