Direct electrochemistry of hemoglobin in layer-by-layer films with poly(vinyl sulfonate) grown on pyrolytic graphite electrodes

Stable layer-by-layer electroactive films were grown on pyrolytic graphite (PG) electrodes by alternate adsorption of layers of polyanionic poly(vinyl sulfonate) (PVS) and positively charged hemoglobin (Hb) from their aqueous solutions. Cyclic voltammetry (CV) of {PVS/Hb}n films showed a pair of well-defined and nearly reversible peaks at about −0.28 V vs. SCE at pH 5.5, characteristic of Hb heme Fe(III)/Fe(II) redox couple. The process of {PVS/Hb} bilayer growth was monitored and confirmed by CV, X-ray photoelectron spectroscopy (XPS) and UV–Vis spectroscopy. While the amount of Hb adsorbed in each bilayer was the same, the amount of electroactive Hb in each bilayer decreased dramatically with increase of the number of bilayer, and electroactivity was just extended to 8 {PVS/Hb} bilayers. CVs of {PVS/Hb}8 films maintained stable in buffers containing no Hb. Positions of Soret band of Hb in {PVS/Hb}n films grown on transparent glass slides suggest that Hb in the films keeps its secondary structure similar to its native state in a wide pH range. Trichloroacetic acid and nitrite were catalytically reduced by {PVS/Hb}8 films with significant lowering of the electrode potential required.