In this book, the authors present topical research in the study of the preparation, properties and use of silica nanoparticles. Topics discussed include the reactivity of inorganic radicals and excited triplet states in colloidal silica suspensions; multifunctional mesoporous silica nanoparticles for controlled drug delivery, multimodal imaging and simultaneous imaging and drug delivery; monodisperse luminescent silica nanoparticles and their application to DNA microarray technology