Biocompatible nanoparticle compositions and methods

Various compositions, methods, and devices are provided that use fluorescent nanoparticles, which can function as markers, indicators, and light sources. The fluorescent nanoparticles can be formed from a fluorophore core surrounded by a biocompatible shell, such as a silica shell. In one embodiment, the fluorescent nanoparticles can be delivered to tissue to mark the tissue, enable identification and location of the tissue, and/or illuminate an area surrounding the tissue. In another embodiment, the fluorescent nanoparticles can be used on a device or implant to locate the device or implant in the body, indicate an orientation of the device or implant, and/or illuminate an area surrounding the device or implant. The fluorescent nanoparticles can also be used to provide a therapeutic effect.