dc.description.abstract | The adsorption of cyanide (CN-) on Au(100) electrode was first examined by high resolution scanning tunneling microscope (STM) in 0.1 M sulfuric acid. The Au(100) electrode assumed that hex reconstruction structure at -0.2 V, which transformed into the (1 × 1) phase upon the addition of KCN, as revealed by real – time in situ STM imaging. The details of this phase transition have been revealed. As the potentials was made positive, oxidation occurred to produce AuCNad en route to anodic etching leading to a leaf-like surface morphology. Cyanide was irreversibly adsorbed to the Au(100) electrode, yielding linear features at negative potentials and a maze-like structure. These features were also found in pH 7 KCN solution. At positive potentials, the Au(100) surface dissolved, creating shallow pits on Au atom in depth. This etching process was slow enough that one could use STM to follow this event.
In 0.1 M KClO4 the adsorption of CN caused the Au(100) surface faceting into the fcc(210) structure, creating a more stable six – fold coordination environment for CN. At positive potentials, two oxidation steps, O1 and O2, can be distinguished, which are outlined as AuCN-ad → AuCNad + e-, and consecutive reactions AuCNad + CN- → Au(CN)2- and Au (exposed) + CN- → AuCNad + e-. The first reaction resulting in a order-to-disorder trasntion, The first reaction resulting in an order-to-disorder transition, causes the (2 × 2) structure to become disordered. The etching of Au(100) in the second process was also observed.
It is noteworthy that the adsorption of CN could produce depressed trenches on the Au(100) electrode in pH 7 KClO4. These surface features could serve as templates for fabricating Au surface alloys by depositing a foreigner metal, such as copper. The adsorption of KCN and the subsequent etching process are highly dependent on the concentration of KCN and the pH value. Gold electrode would dissolve faster with an increase of KCN concentration in more alkaline solutions.
The electrochemical detection of dopamine was examined by using an ordered Au(100) electrode in 0.1 M sulfuric acid. The oxidation of dopamine is evident in a cyclic voltammetric experiment with Au(100) electrode in a solution containing 1 mM ascorbic acid (AA) and 1 µM dopamine. This feature was not observed with Au disk and Au(111) electrodes, reflecting the importance of surface structure of Au electrode in conducting electrochemical analysis of dopamine. In 0.1 M PBS containing 1 mM AA, the detection limit for dopamine is approximately 50 µM, which is inferior to that found in acidic solutions. This contrast is attributed to the influence of anions (AA-, PO4-) that were adsorbed on the Au(100) electrode. Moreover, the redox features of dopamine appeared to be more irreversible. Modification of halides or pseudohalides on the Au(100) surface can inhibit the oxidation of AA, which speaks to the polarities of these entities and the suppressive effect on the diffusion of AA to electrode.
Finally, among the five halides and pseudohalides studied in the current study, KCN is the most suitable modifier to analyze dopamine. The CN-coated Au(100) electrode can detect dopamine down to 5 µM in a solution containing 1 mM AA. In comparison, the detection limit is 50 µM for a bare Au(100) electrode. | en_US |