Fibrous nanocrystals of hydroxyapatite loaded with TiO₂ nanoparticles for the capture and photocatalytic decomposition of specific proteins

The monomolecular adsorption of lysozyme (LSZ) and bovine serum albumin (BSA) on hydroxyapatite (HAp) was observed by using two types of fibrous crystals elongated in the c-axis. Selective removal of the specific proteins was achieved by the capture and decomposition on the HAp crystals having the particular nanostructures attached with anatase-type TiO₂. Bundled short nanorods of ca. 10nm in diameter were suitable for the capture of a relatively small protein molecule, LSZ, due to their high specific surface area, while the adsorption of a relatively large molecule, BSA, was restricted because of the narrow clearance gap between the nanorods. On the other hand, the large protein preferentially adsorbed to long nanoneedles of 30-60nm in diameter, which had a wide gap among the loosely aggregated crystals. The captured proteins were smoothly decomposed with anatase nanoparticles loaded on the fibrous HAp crystals under UV irradiation. Thus, the photocatalytic activity for the decomposition of proteins could be controlled with the adsorption on the surface of the nanostructured HAp crystals.