Copper,as a transition element,plays critical roles in physiological and pathological events during life processes.However,this heavy metal ion is also highly toxic to organisms,since exposure to high levels of Cu2+ ions can lead to serious liver and kidney damages and even cause neurodegenerative diseases [1].Therefore,analysis and measurement of copper in environmental and biological samples are highly desirable.Quartz crystal microbalance (QCM) is a powerful mass sensor for specific analysis and detection of various molecular events in a label-free fashion [2,3].However,the application of QCM into the determination of small molecules is still a challenge due to its relatively low frequency shift.In this work,a novel QCM sensor for the rapid and sensitive detection of Cu2+ ions was developed.Gold nanoparticles (NPs) were self-assembled on the sensor surface,which greatly increased surface area for the immobilization of the recognition ligand 3-mercaptopropionic acid (3-MPA).Comparing with the sensor directly modified with 3-MPA,this sensor with additional gold NPs layer showed significantly amplified signal and enhanced sensitivity.The detection limit of Cu2+ ions decreased to 0.2 mg/L,which is sufficient for monitoring the level of Cu2+ in drinking water.Highly specific detection of Cu2+ ions in aqueous solution was achieved in 15 min,while the frequency changes from control metal ions were negligible.Moreover,this obtained QCM can be easily regenerated and reused for more than twenty times without obvious decrease of response signal.Further application of the QCM sensor into the determination of copper ions in real sample was also realized.With the nanoparticle based signal amplification,QCM sensor is also promising in the detection and analysis of small molecules in environmental and biological samples.