The present invention provides a cost-efficient method for producing particles having a SiO2 containing surface wherein said method comprises a) providing an aqueous reaction composition comprising i) core particles, ii) an added base, iii) a silicate salt, and iv) a pH modulator wherein the pH value of the reaction composition is above the gelation pH value; b) agitating said reaction composition, wherein the pH modulator decreases the pH value of the reaction composition over time and wherein due to said decrease of the pH value of the reaction composition SiO2 is deposited onto the core particles, whereby particles are formed which have a diameter of 30 μm or less; and c) obtaining the particles. Furthermore, silica particles having high nucleic acid binding properties are provided.