Electrochemiluminescence (ECL) emission of gold nanoparticles (Au NPs) loaded graphitic carbon nitride nanosheets (Au-CNN nanohybrids) can be modulated by the Au content. On the basis, a signal-on ECL sensor for detecting cyanide, a widespread toxic chemical, has been developed in this work. The sensor utilizes cyanide-mediated etching of Au NPs to recover the ECL emission of Au-CNN nanohybrids initially inhibited by Fo rster resonance energy transfer (FRET) from CNNs to Au NPs. The ECL sensor has a sensitive response to cyanide in the range of 50 nM to 1mM with a detection limit of 50 nM, and shows high specificity due to the high affinity of Au-cyanide complex. The proposed FRET modulated ECL sensor may prove valuable in future environmental monitoring. (c) 2017 Elsevier Ltd. All rights reserved.