Reactive oxygen species(ROS)are largely produced under pathological situations.To understand the etiology of disease,it is urgent to develop efficacious probes for detecting ROS.Herein,we report a novel nano-conjugates detection system constructed from gold clusters(AuNCs)and quantum dots(QDs)for fluorescence ratiometric sensing ROS.The AuNCs and QDs particles are conjugated into one nanoparticle throughout the covalent binding of the active groups on the surface of the nanoparticles.Upon interacting with ROS,the red AuNC-QD emission fluorescence(645nm from QDs)in the detection system was gradually decreased,while the green fluorescence(480nm from AuNCs)intensity changed little.The fluorescence ratio at the two wavelengths(I480nm/I645nm)is linear correlated with the ROS which could be used for the real time ratiometric detection of ROS.By taking advantage of the uptaking ability of living cells to nanopartilces,the developed nano-conjugates could be applied to monitor the ROS in living cells.The stimulated ROS in living cells(RAW264.7)were monitored by the AuNC-QD and the results are consistent with the traditional DCFH-DA method,confirming the reliability of the developed method.Featured with the merits of higher photostability,low background noise,high accuracy of ratiometric detection,the AuNC-QDs conjugate demonstrated its promising probe for realtime ROS detection in living cells.