Three-dimensional microscale assemblies of fluorine-doped titania nanoparticles were synthesized from silica-based diatom microshells (frustules) via a shape-preserving reactive conversion process (as per the method of Unocic et al.). The nanostructured F-doped titania frustules were found to induce rapid hydrolysis of the organophosphorous esters, methyl paraoxon, and methyl parathion (insecticides and nerve agent mimics), under mild conditions (pH 4.5-7.9, 22 degrees C) and in the absence of light. Fluorine doping of the titania frustules, which altered the surface Lewis acidity, was found to have a strong impact on the rate of hydrolysis.