Comparative permeation study of different types of myoglobin layer-by-layer films and the effect of film permeability on their electrochemistry and electrocatalysis

Three different types of myoglobin (Mb) layer-by-layer films were assembled respectively with TiO2 sol-gel by vapor-surface deposition, TiO2 nanoparticles, and poly (styrenesulfonate), designated as {SG-TiO2/Mb}(n), {NP-TiO2/Mb}(n), and {PSS/Mb}(n). The permeability of the films was studied and compared by rotating disk voltammetry (RDV) and electrochemical impedance spectroscopy (EIS) with different electroactive probes, showing a general permeability sequence of {SG-TiO2/Mb}(n) > {NP-TiO2/Mb}(n) > {PSS/Mb}(n). The electrochemical and electrocatalytic activity of Mb in these films were also investigated and compared by cyclic voltammetry (CV), RDV, and amperometry, indicating that among the three Mb films, {SG-TiO2/Mb}(n) films demonstrated the highest maximum surface concentration of electroactive Mb and the best electrocatalytic performances toward reduction of H2O2. All these advantages could be attributed to the unique architecture and porous structure of {SG-TiO2/Mb}(n) films, which could greatly facilitate the mass transport of small counterions and catalytic substrates within the films. The various influencing factors on the permeability, electrochemistry, and electrocatalysis of the Mb films were also investigated in detail.