Layer-by-layer assembly of myoglobin and nonionic poly(ethylene glycol) through ion–dipole interaction: An electrochemical study

Nonionic poly(ethylene glycol) (PEG) and myoglobin (Mb) were successfully assembled into {PEG/Mb}n layer-by-layer films on various solid surfaces. Quartz crystal microbalance (QCM), UV–vis spectroscopy and cyclic voltammetry (CV) were used to monitor and confirm the film growth and characterize the films. The Mb in stable {PEG/Mb}n films showed a quasi-reversible CV response for its heme Fe(III)/Fe(II) redox couple, and was used to electrocatalyze the reduction of various substrates. The interaction between PEG and Mb in the assembly was investigated in detail. A series of comparative experiments showed that the ion–dipole interaction between positively charged groups on the Mb surface and electronegative ether oxygen groups of PEG would be the main driving force for the assembly of {PEG/Mb}n films, while other interactions such as hydrogen bonding and/or hydrophobic interaction may also play an important role in stabilizing the films in blank buffers.