Redox properties of ferricyanide ion on layer-by-layer thin film-coated gold electrodes; effects of type of polycationic components in the film

The surface of a gold (Au) electrode was coated with layer-by-layer (LbL) thin films composed of poly(vinyl sulfate) (PVS) and different type of poly(amine)s including poly(allylamine) (PAH), poly(ethyleneimine) (PEI) and poly(diallyldimethylammonium chloride) (PDDA) and redox properties of ferricyanide ion ([Fe(CN)₆]^3-) on the LbL film-coated Au electrodes were studied. The LbL film-coated electrodes exhibited redox response to [Fe(CN)₆]^3- ion when the outermost surface of the LbL film was covered with the cationic poly(amine)s while virtually no response was observed on the LbL film-coated electrodes whose outermost surface was covered with PVS due to an electrostatic repulsion between [Fe(CN)₆] ^3- ion and the negatively-charged PVS layer. The redox properties of [Fe(CN)₆]^3- ion on the LbL film-coated electrodes significantly depended on the type of polycationic materials in the LbL film. The LbL film-coated electrodes which had been immersed in the [Fe(CN) ₆]^3- solution for 15 min exhibited redox response even in a [Fe(CN)₆]^3- ion-free buffer solution, suggesting that [Fe(CN)₆]^3- ion is confined in the films. In the buffer solution, redox peaks were observed between +0.1 and 0.4 V depending on the type of polycations in the film. Thus, [Fe(CN)₆]^3- ion can be confined in the film and the redox potential is polycation-dependent.