| Abstract
| - The displacement adsorption process of 4-mercaptopyridine (4-MP) on trisodium citrate preadsorbedgold surface in aqueous solution was studied using atomic force microscopy (AFM). The measurement wasdone by monitoring the interaction force between a gold-coated AFM tip and a gold substrate, bothpresaturated by trisodium citrate. The addition of 4-MP was found to result in a remarkable change oftip−substrate adhesion force, which showed a gradual increase and finally reached a maximum. Usingthe chemical force titration technique, we estimated the surface pK1/2 of thus-formed 4-MP displacementfilm and compared with pure 4-MP self-assembled monolayer (SAM) formed on gold in ethanol solution.Our results indicate that the 4-MP molecules are more strongly adsorbed on gold than citrate anions,mostly via Au−S bonding, forming a less dense and mixed displacement film. The displacement adsorptionkinetics seems very fast and it takes only ca. 2 min to establish more than 50% surface coverage of 4-MPmolecules.
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