The highly solubile and photocatalytic carbon quantum dots(CDs) were prepared by a one-pot hydrothermal method.The CDs could oxidize the typical substrate of 3,3-,5,5-tetramethylbenzidine(TMB) of the horseradish peroxidase(HRP) under visible light(λ≥400 nm) irradiation causing the color signal.In this assay,the interaction between copper ion and CDs will suppress the oxidase mimicking activity of CDs.Upon introduction of target pyrophosphate ions(ppi) into the detection system,the Cu2+-ppi complexes were forming on the basis of the coordination reaction between copper ion and inorganic pyrophosphate ions,thus the oxidase mimicking activity of released CDs was recovered.Based on this characteristic,a colorimetric sensor for the ppi detection was designed.Under the optimal conditions,the obtained colorimetric signal showed a linear response to ppi within a dynamic range of 1.0×10-6-5.0×10-3 mol/L with a detection limit(LOD) of 2.5×10-7 mol/L.The method was applied in the determination of ppi in human plasma samples,with recoveries of 97.4%-104.8%.The results showed that the colorimetric sensor could be used to detect ppi in human plasma samples.