Gas-phase self-assembly of spherical TiO2 nanoparticle cluster (TiO2-NPC). Noble metal nanoparticles are homogeneously decorated in TiO2-NPC. Tunable particle size and chemical composition of the hybrid nanostructure. Activity determined by light irradiation and ligand-nanoparticle interaction. Enhanced activity by silver nanoparticle in the presence of bovine serum albumin.