Figure 2.

(a) Normal Raman (NR) for the solid state of DDTC and SERS spectra of DDTC, DDTC-Zn²⁺, and DDTC-Cu²⁺ on AuNPs. In the case of the DDTC-Cu²⁺ complex, the vibrational band at ~1490 cm⁻¹ was prominently blueshifted to ~1504 cm⁻¹, as marked in red arrows. (b) The SERS spectra of DDTC-metal complexes on AuNPs for Cu²⁺, Zn²⁺, Pb²⁺, Ni²⁺, NH₄⁺, Na⁺, Mn²⁺, Mg²⁺, K⁺, Hg²⁺, Fe²⁺, Fe³⁺, Cr³⁺, Co²⁺, Cd²⁺, and Ca²⁺.