Preparation of ferrocene-terminated layers by direct reaction with glassy carbon: a comparison of methods

Monolayers and sub-monolayers of ferrocene (Fc) groups were immobilised on glassy carbon by direct reactions of primary amine and carboxylic acid derivatives of Fc. Reaction of FcCH2NH2 with polished GC in acetonitrile at open circuit potential yielded grafted layers with surface coverages up to ∼70 % of a close-packed monolayer. The influence of the solvent and applied potential during the reaction was consistent with a Michael-like addition mechanism at the surface. When FcCH2NH2 was reacted with GC under conditions that promote amide bond formation, sub-monolayers of Fc groups were attached; however, the participation of the Michael-like addition reaction as the major immobilisation pathway could not be discounted. Activation of FcCOOH and FcCH2COOH with oxalyl chloride and reaction with polished GC gave surface coverages of Fc corresponding to ∼25 % of a close-packed monolayer. Ester bonds are assumed to form in these reactions. The modification methods investigated here are experimentally simple and are very suitable for use with high surface area carbons. Furthermore, they may be the method of choice for applications where multilayer coatings must be avoided.