Direct electron transfer and electrocatalysis of myoglobin loaded in layer-by-layer films assembled with nonionic poly(ethylene glycol) and ZrO2 nanoparticles

Nonionic poly(ethylene glycol) (PEG) and ZrO2 nanoparticles were successfully assembled into {PEG/ZrO2}n layer-by-layer films on solid surfaces through coordination interaction between the ether oxygen groups in PEG and the Zr(IV) in ZrO2 nanoparticles. The {PEG/ZrO2}n films were then immersed in myoglobin (Mb) solution at pH 5.0 to load Mb into the films, designated as {PEG/ZrO2}n–Mb. Cyclic voltammetry (CV), quartz crystal microbalance (QCM), and scanning electron microscopy (SEM) were used to characterize both {PEG/ZrO2}n and {PEG/ZrO2}n–Mb films. Mb in the {PEG/ZrO2}n–Mb films fabricated on pyrolytic graphite (PG) electrodes showed direct and quasi-reversible CV response, which could be used to electrocatalyze reduction of oxygen and hydrogen peroxide. The interaction between Mb and {PEG/ZrO2}n films in loading was also discussed and explored. The results suggest that the electrostatic interaction is the main driving force for the loading of Mb into the {PEG/ZrO2}n films, while hydrogen bonding and/or hydrophobic interaction are also important factors for stabilizing {PEG/ZrO2}n–Mb films in blank buffers. The comparative experiments demonstrated that only those heme proteins whose dimension was smaller than the average pore size of the films were able to be loaded into the films and exhibited electroactivity.