The concept of mesoporous silica functionalization via metalorganic reagents, demonstrated with phenyllithium, is transferred from micrometer-sized MCM-41 materials to colloidal suspensions containing mesoporous silica nanoparticles. Due to the different nature of the nanosized system, particle agglomeration and coalescence were found to be a major issue. Various approaches for the preparation of anhydrous colloidal systems via removal of water from the mesopores were compared. It was found that the most promising approaches for water removal at temperatures below 100 degrees C are the controlled hydrolysis of additives (triethyl orthoformate) and absorption from the vapor phase by molecular sieves. Both methods avoid the hydrolysis of the phenyllithium reagent and yield nonagglomerated suspensions of phenyl-functionalized colloidal mesoporous silica nanoparticles, thus demonstrating the feasibility of the metalorganic conversion route in nanosized porous silica systems.