Nano-encapsulated photosensitizers and their use in the treatment of tumors and/or imaging is described. Preferably, the photosensitizers are encapsulated in a calcium phosphate nanoparticle (CPNP). Encapsulating the PS in a CPNP increases the half-life of the PS, increases absorption of the PS into the target cell tissue, increases the photostability of the PS, increases the photoefficiency of the PS, increases in vivo retention of the PS, or combinations thereof, ultimately making it a highly efficacious agent for use in photodynamic therapy, imaging target tissues, vessels, or tumors, and/or detecting or locating tumors.