Electrochemical detection of Cd²⁺ ions by a self-assembled monolayer of 1,9-nonanedithiol on gold

The application of 1,9-nonanedithiol (NDT) self-assembled monolayer (SAM) on gold for the electrochemical determination of Cd²⁺ was studied. Interestingly, we found that a NDT SAM strongly affects the stripping wave of Cd, resulting in a sharp peak that was used for electroanalytical determination of Cd²⁺ in aqueous solutions. The different parameters, such as potential and time of deposition of Cd, were examined. Furthermore, polarization-modulated infrared reflection absorption spectroscopy (PM IRRAS) and X-ray photoelectron spectroscopy (XPS) were used for exploring the interaction between the deposited Cd and the thiol groups on Au. FTIR measurements clearly indicate that NDT is assembled in a disordered liquid type monolayer interacting with the Au electrode via both thiol moieties. XPS reveals that Cd is stripped at two different potentials and that the signal of sulfur is almost unchanged by deposition and desorption of Cd. All these finding allude to the interesting conclusion that Cd is deposited on Au lifting to some extent the thiol groups.