Electrochemical characteristics of ferrocenecarboxylate-coupled aminoundecylthiol self-assembled monolayers.

The electrochemical characteristics of the modified electrodes with ferrocenecarboxylate-coupled aminoundecylthiol monolayers prepared in two sequential steps were studied. The self-assembled monolayer (SAM) was prepared through the covalent attachment of ferrocenecarboxylate in an activation solution containing N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide coupling agent to aminoundecylthiol SAMs formed on a substrate. In the ferrocenecarboxylate-coupled aminoundecylthiol monolayers, the ferrocene moieties were expected to be packed regularly with enhanced ordering compared with those in the FcCOO(CH2)11SH monolayer. As the ferrocene coverage increases, the formal potential for the ferrocene-ferricenium (Fc/Fc+) couple shifts to the positive potential and the full width at half-maximum (deltaE(fwhm)) increases also. The maximum coverage is found to be about 3 x 10(-10) mol cm(-2), which is considered to be a value obtained from a well-ordered ferrocene-tethered SAM. As for the mass change, the increase in ferrocene coverage caused the enhancement in ion association between the ferricenium cations and perchlorate anions resulting in a mass increase upon oxidation; however, the mass change per mole electron decreases. The results obtained from the ferrocenecarboxylate-coupled aminoundecylthiol monolayers were explained to be due to the well-ordered packing with regular spacing compared with those of the FcCOO(CH2)11SH monolayer.