Mesoporous oxide nanoparticles, compositions comprising such nanoparticle, and methods of making and using such nanoparticles. The nanoparticles (e.g., compositions comprising the nanoparticles) have an average size of less than 15 nm and a narrow size distribution. The nanoparticles can be used in imaging applications and delivery of molecular cargo (e.g., a drug) to an individual.