Influences of geometrical topography and surface chemistry on the stable immobilization of adenosine deaminase on mesoporous TiO₂

Mesoporous TiO₂ microparticles featuring distinct, well-defined pore sizes (3.7-40nm) were used for investigating the effect of geometrical topography and surface chemistry on the immobilization of adenosine deaminase (ADA). We determined that the pore size of the microparticles can be tuned by varying the post-heat-treatment process. The ADA-adsorption properties of microparticles displaying distinct geometrical topographies were compared, and the relations between pore sizes and the levels of protein loading and enzyme activity were investigated. Although the specific surface area of large-pore microparticles was smaller than that of microparticles harboring small pores, carriers derived from large-pore microparticles exhibited comparatively superior enzyme loading; an overall enzyme loading of 13.5mg/g was achieved in the case of TiO₂ carriers featuring 20nm intra-particle pores. In order to strengthen operational stability, surface modification with (3-aminopropyl) triethoxysilane (APTES) and crosslinking with glutaraldehyde were performed; the operational stability of ADA immobilized on TiO₂-APTES microparticles featuring various pore sizes was considerably higher than that of ADA immobilized on blank TiO₂. Thus, both the geometrical topography and surface chemistry of mesoporous TiO₂ microparticles and ADA were crucial for achieving high biocatalysis activity and operational stability.