Direct Electrochemistry and Surface Plasmon Resonance Characterization of Alternate Layer-by-Layer Self-Assembled DNA−Myoglobin Thin Films on Chemically Modified Gold Surfaces

Alternate layer-by-layer (L-by-L) polyion adsorption onto gold electrodes coated with chemisorbed cysteamine gave stable, electroactive multilayer films containing calf thymus double stranded DNA (CT ds-DNA) and myoglobin (Mb). Direct, quasi-reversible electron exchange between gold electrodes and proteins involved the Mb heme Fe 2+ /Fe 3 + redox couple. The formation of L-by-L (DNA/Mb) n films was characterized by both in situ surface plasmon resonance (SPR) monitoring and cyclic voltammetry (CV). The effective thickness of DNA and Mb monolayers in the (DNA/Mb) 1 bilayer were 1.0±0.1 and 2.5±0.1 nm, corresponding to the surface coverage of ∼65% and ∼89% of its full packed monolayer, respectively. A linear increase of film thickness with increasing number of layers was confirmed by SPR characterizations. At pH 5.5, the electroactive Mb in films are those closest to the electrode surface; additional protein layers did not communicate with the electrode. CV studies showed that electrical communication might occur through hopping conduction via the electrode/base pair/Mb channel, thanks to the DNA−Mb interaction. After the uptake of Zn 2+, a special electrochemical behavior, where MbFe 2 + acts as a DNA-binding reduction catalyst in the Zn 2+ −DNA/Mb assembly, takes place.