Figure 1.

(a) Photo of DDTC and DDTC-metal complexes for NH₄⁺, K⁺, Ca²⁺, Mg²⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, Co²⁺, Cr³⁺, Ni²⁺, Fe²⁺, Fe³⁺, Cu²⁺, and Mn²⁺ ions. (b) UV-Vis absorption spectra of DDTC-metal complexes. The inset shows the absorption bands at ~450 nm and the photo of DDTC-Cu²⁺ complex corresponding to various concentrations of the Cu²⁺ ion. (c) UV-Vis absorption spectra of AuNPs and DDTC-metal complexes on AuNPs. The inset shows the TEM image of the AuNPs-DDTC-Cu²⁺ complex. The scale bar is 100 nm. (d) High-resolution image of AuNPs with a scale bar of 5 nm. Photo of AuNPs and DDTC-metal complexes on AuNPs.