The particle size, crystallinity, porosity, and shape can be precisely manipulated, enabling the silica nanoparticles for various applications. Moreover, numerous available surface modifications of silica nanoparticles permit their control of surface chemistry to achieve drug loading, good dispensability, and site-specific targeting. These properties, if combined and developed appropriately, make silica nanoparticles a platform for biomedical imaging, detecting, therapeutic delivery, monitoring, and ablative therapies. With the design of diverse dopants, surface functional groups, and assembly techniques, multifunctional nanoparticles can be developed with theranostic applications. Silica nanoparticles have also widely applied in other areas such as energy source, electronic, sensor, and catalysis purposes.