This invention relates to the development of a new Raman enhancing reagent and a surface-enhanced Raman scattering (SERS) method for rapid and ultra-sensitive detection and identification of perchlorate (ClO4−) and other anions such as technetium (TcO4−), uranium and nitrate in environmental samples. The method involves the synthesis of controlled gold nanoparticles which are modified with amine functional groups such as 2-(dimethylamino)ethanethiol and N,N,N-trimethylaminethiol. These functionalized Au nanoparticles were found to be reactive with perchlorate and other anions and can be used to detect these anions by Raman spectroscopy at ultra low concentrations in complex environmental matrices. This invention overcomes the limitations of currently-available analytical techniques by offering an inexpensive, rapid, ultra-sensitive, and real-time identification and detection of perchlorate and other anions. The technique is not only sensitive but also highly specific because of the unique Raman vibrational bands of perchlorate and other anions.