Self-assembly of electroactive layer-by-layer films of heme proteins with anionic surfactant dihexadecyl phosphate Original Research Article

Anionic surfactant dihexadecyl phosphate (DHP) with two hydrocarbon chains can be self-assembled into a double-layer structure with tail-to-tail configuration and negatively charged head groups toward outside in its aqueous dispersion. Due to this unique biomembrane-like structure, the “charge reversal” in DHP adsorption on solid surface was realized, and the DHP was successfully assembled with positively charged myoglobin (Mb) or hemoglobin (Hb) into {DHP/protein}n layer-by-layer films. Quartz crystal microbalance (QCM), UV–vis spectroscopy, and cyclic voltammetry (CV) were used to monitor or confirm the film assembly process. The {DHP/protein}n films grown on pyrolytic graphite (PG) electrodes showed a pair of well-defined and nearly reversible CV peaks at about − 0.35 V vs SCE in pH 7.0 buffers, characteristic of the protein heme Fe(III)/Fe(II) redox couples. Based on the direct electrochemistry of heme proteins, the {DHP/protein}n films could also be used to electrochemically catalyze reduction of oxygen, hydrogen peroxide and nitrite with significant lowering of reduction overpotentials. Scanning electron microscopy (SEM), UV–vis spectroscopy, and reflectance absorption infrared (RAIR) spectroscopy were employed to characterize the {DHP/protein}n films, suggesting that the proteins in the films retain their near-native structure.