The present invention relates to core shell silica particles, wherein each core shell silica particle comprises a silica core, and a surface of the silica core is etched with metal silicate, the core shell silica particles prepared by: i) admixing an amount of silica particles in water with an amount of a base, wherein the base comprises a monovalent metal ion, to produce core shell silica particles, each core shell silica particle comprising a silica core, and a surface of the silica core etched with a silicate of the monovalent metal ion; and ii) reacting the core shell silica particles formed in step i) with a metal salt comprising a second metal ion, to form core shell silica particles comprising silicate of the second metal ion on the surface of the silica core.