The ability to study biological events on the cellular or molecular levels is important in understanding disease pathology and therapeutic efficacy, and the development of imaging agents targeted to specific biological structures or disease markers can help to elucidate the chemical processes occurring at various stages of treatment or disease. Thus, nanometer sized, inorganic particles with at least one imaging handle are attractive candidates for the study of cellular and sub-cellular processes because they are on the order of the physical dimensions of many biological structures including: DNA, oligonucleotides, and antibodies. They are also attractive candidates for imaging relative to small molecule reagents, due to the collective properties exhibited by a relatively large number of atoms.
