Here in this work, we report the fabrication of a (metal) ion selective surface enhanced Raman scattering (SERS) optrode, the counterpart of an ion selective electrode, for the detection of metal ions in solution. Following our previous work, a layer-by-layer self-assembly strategy was used to fabricate the SERS optrode, followed by modification with an ion chelating reagent, 4-(4-phenylmethanethiol)-2,2′:6′,2′′-terpyridine (PMTTP). The SERS spectrum change after binding with metal ions was used to identify and detect metal ions in solution. Cd²⁺ in aqueous solution was chosen as a sample analyte. Similar to standard pH measurement, through simple single point known standard solution calibration, a quick (semi-)quantitative analysis of Cd²⁺ was realized.