AuNPs capped with 5-mercaptomethyltetrazole have been prepared which are water-soluble and biocompatible.An assay for the determination of Pb2+ has been proposed based on aggregation fo funcational AuNPs in the presence of Pb2+.With colorimetry,Pb2+ can be detected at a level of 30riM (~7 ppb).Under the optimum conditions,the response is linearly proportional to the concentration of Pb2+ in the range 0.20-5.06 ppm.In addition to high sensitivity,the above sensing systems exhibit good selectivity for Pb2+ over other metal ions.These results demonstrate the facility and effectivity of our functional Au nanoparticles sensor for quantitative Pb2+ analysis.The mechanism of this strategy is also discussed.The assay may become useful in the environment monitoring,water quality inspection and biomedical diagnosis as well.