Adsorption and Direct Electron Transfer from Hemoglobin into a Three‐Dimensionally Ordered Macroporous Gold Film

Application of protein‐based, direct electron communication in bioelectronic devices, biosensors, or biofuel cells usually requires high stability and function density of the immobilized proteins or enzymes. Traditional methods have been used to increase the function density using multilayer immobilization techniques at the expense of losing stability and electron‐communication rate, that is, generally only protein molecules near the electrode surface are electroactive. In order to overcome the above problems, a three‐dimensional, ordered, macroporous gold film electrode is synthesized electrochemically by an inverted colloidal crystal template technique. The uniform, three‐dimensional macroporous gold provides superior conductivity, high stability, and large surface area. Its interconnected macroporous structure, containing gold nanoparticles, significantly enhances the amount of adsorbed hemoglobin (Hb) molecules at the monolayer level and also provides a good microenvironment for retaining the biological activity of the adsorbed protein, as confirmed by electrochemical and attenuated total reflection Fourier‐transform infrared spectroscopy. Therefore, direct electron transfer between the adsorbed Hb and the electrode is achieved. Adsorption of Hb on the macroporous gold film electrode is monitored using electrochemical impedance spectroscopy. The saturated adsorption amount, Γ, of the Hb is determined to be 6.55×10^–10 mol cm^–2 with a surface coverage of 88.1 %. The electrochemical behavior and the adsorption mechanism of Hb on the macroporous gold film electrode are discussed on the basis of the experimental results.