Growth and electrochemical activity of the poly-l-lysine|poly-l-glutamic acid thin layer films: an EQCM and electrochemical study

Quartz crystal microbalance (QCM) measurement and cyclic voltammetry were used to study the layer-by-layer growth of poly-l-lysine (p-Lys) and poly-l-glutamic acid (p-Glu) thin films and their ability to act as support for redox relays between metal electrodes and redox species in organic electrolytes. The mass of the film grown from buffered solution at constant pH depends on the composition of the buffer used. The growth proceeds in several stages with different mass increments for each poly-l-lysine and poly-l-glutamic acid layer. Ferro/ferricyanide confined into the polypeptide films can play the role of a redox relay between the electrode surface and the organic electrolyte. This was demonstrated on the impregnated polypeptide film|1,2-dichloroethane interface with decamethylferrocene dissolved as redox species in the organic phase. The transport of the ferro/ferricyanide in the polypeptide film is the rate limiting step of the electron transfer process. The diffusion coefficient of the ferro/ferricyanide determined from voltammetric experiments was of the order of 10−11–10−12 cm2 s−1. The bimolecular rate constant of the electron transfer reaction was found to be 0.2 cm s−1 M−1.