In the present study, surface-enhanced Raman spectra of a bifunctional Raman reporter, 2-mercaptobenzimidazole, has been found to be responsive exclusively towards Cu2+ ions while the reporter remains anchored on the Au nanoparticle surface. Thus a specific Cu2+-ion-detection protocol emerges. The simplicity, sensitivity, and reproducibility of the method allow routine and quantitative detection of Cu2+ ions. An interference study involving a wide number of other metal ions shows the procedure to be uniquely selective and analytically rigorous. A theoretical study was carried out to corroborate the experimental results. Finally, the method is promising for real-time assessment of Cu2+ ions in aqueous samples and also has the ability to discriminate CuI and CuII ions in solution.