Fibrillar superstructure formation of hemoglobin A and its conductive, photodynamic and photovoltaic effects

The fabrication of biomaterials which serve as functional scaffolds exhibiting diversified effects has been valued. We report here a unique strategy to fibrillate hemoglobin A (HbA), which exhibits multiple photoelectrochemical properties, and a subsequent specific defibrillation procedure. A subtle structural rearrangement of the α/β-subunits within the quaternary structure of HbA is responsible for the HbA fibril formation in the presence of 0.5% CHCl3. The narrow pH dependence of the suprastructure formation around pH 7.4 illustrates the highly sensitive nature of the structural alteration. The CHCl3-induced fibrils become disintegrated by ascorbic acid, indicating that the oxidation–reduction process of the iron within the heme moiety could be involved in stabilization of the fibrillar structures. The electron-transferring property of the iron allows the fibrils to exhibit not only their conductive behavior but also a photodynamic effect generating hydroxyl radicals in the presence of H2O2 with light illumination. A photovoltaic effect is also demonstrated with the HbA fibrils, which generate an electric current on the fibril-coated microelectrode upon irradiation at 405 nm. Taken together, the multiple effects of HbA fibrils and the selective fibrillation/defibrillation procedures could qualify the fibrils to be employed for various future applications in biotechnology, including bio-machine interfaces.