Comparative electrochemical study of myoglobin loaded in different polyelectrolyte layer-by-layer films assembled by spin-coating

Different types of {polycation/polyanion}n layer-by-layer (LBL) films were assembled on the surface of pyrolytic graphite (PG) electrodes by spin-coating, and then immersed in myoglobin (Mb) solutions at pH 5.0 to load Mb into the films. Compared with the traditional solution-dipping method in LBL assembly, the spin-coating approach was much more time saving but did not show substantial difference in Mb loading. The Mb-loaded LBL films demonstrated nearly reversible cyclic voltammetric (CV) responses for Mb Fe(III)/Fe(II) redox couple, and the surface concentration of electroactive Mb in the films (Γ*, mol cm−2) could be used to compare the loading behaviors of Mb in different films. Among the six polyelectrolyte LBL films, {HECE/PSS}n films assembled with quaternized hydroxyethyl cellulose ethoxylate (HECE) and poly(styrenesulfonate) (PSS) demonstrated the largest Γ* value for loaded Mb and the best performance in electrocatalysis toward hydrogen peroxide. CV, UV–vis spectroscopy and electrochemical impedance spectroscopy (EIS) were used to characterize the films and explore the reason why {HECE/PSS}n-Mb films showed better electrochemical response than the other Mb-loaded LBL films. The better understanding of the interactions involved in Mb loading may help us to find novel and more suitable protein-loaded LBL film systems in the future.