Facile synthesis of amino-functionalized mesoporous TiO₂ microparticles for adenosine deaminase immobilization

Fabrication of biocompatible micro- and nanoparticles is attractive because of their potential for application as enzyme immobilization tools. Mesoporous TiO₂ microparticles with high crystallinity, high hydroxyl density, and large pore size (20 nm) were prepared by solid-state calcination and a soft chemistry method. The large pores of the microparticles were efficient in adenosine deaminase (ADA) encapsulation. The hydroxyl-coated microparticles could optimize amino-silane modification and be efficiently utilized as ADA-immobilization carriers. However, the adsorbed enzymes were easily leached when cycled. Sequential application of the coupling agent 3-aminopropyltriethoxysilane and cross-linker glutaraldehyde (GLU) enabled effective ADA coupling. After eight batch cycles, the immobilized ADA retained 80% of its initial activity, much higher than that by direct enzyme adsorption (30%). GLU prevented enzyme desorption and loss of activity. We thus improved ADA loading efficiency, recycling, and stability. TiO₂ microparticles could be suitable ADA immobilization candidates for detection and industrial inosinic acid production.