Spherical particles with an amorphous core of silica and a crystalline shell of titanium oxide (SiO2@TiO2) formed in a three-step procedure, being the last step a mild chemical treatment. SiO2@TiO2 had a shell with pores (micro and mesopores) permeating between TiO2 nanocrystals (anatase) and a solid core of amorphous silica. The spheres had an outstanding specific surface area (300 m(2) g(-1)). A cyto- and genotoxic study of SiO2@TiO2 and titanium oxide nanoparticles (TiO2-NP) on UMR106 cells with 24 h exposure showed that SiO2@TiO2 colloidal particles were less toxic than TiO2-NP. (C) 2012 Elsevier Inc. All rights reserved.