This dissertation describes the use of several different types of nanoparticles for biomedical applications including imaging, drug delivery, and sensing. Several novel contrast agents for magnetic resonance imaging have been developed using different nanoparticle platforms. First, highly efficient T1-weighted contrast agents were developed using mesoporous silica nanoparticles. This system was also extended to form a biodegradable contrast agent based on the same mesoporous silica nanoparticle platform. By incorporating paramagnetic metal ions Gd3+ and Mn2+ into nanoscale metal-organic frameworks, new contrast agents for magnetic resonance imaging have also been developed. All of these systems can also be modified to include either an organic fluorophore or luminescent lanthanide ion, forming multimodal contrast agents that can be used for both optical and magnetic resonance imaging. The use of nanoscale metal-organic frameworks for drug delivery will also be presented. Highly porous nanoscale metal-organic frameworks were synthesized using Fe 3+ and an organic bridging ligand. After the nanoparticles were synthesized, a platinum based anticancer drug was covalently attached to the porous framework. These nanoparticles have also been functionalized with organic fluorophores to create optical contrast agents. Finally, the use of a nanoparticle sensor for the detection of dipicolinic acid, a chemical marker for bacterial endospores (such as Anthrax), is demonstrated. Several different nanoparticle sensors were developed, and they are advantageous over the molecular complexes because they allow for the incorporation of an internal standard, which eliminates the need for instrument specific calibration curves
