The present invention is directed to a nanoparticle loaded with a light sensitive molecule and a method of preparing the nanoparticle, wherein the nanoparticle is a colloidal gold nanoparticle and the light sensitive molecule is non-covalently adsorbed to the surface of the nanoparticle. The present invention is also directed to a nanoprobe comprising the nanoparticle and further comprising a targeting moiety covalently coupled to the surface of the nanoparticle. Additionally, the present invention is directed to an imaging method comprising administering the nanoprobe to a subject and collecting imaging data of the subject or part of the subject with optical multimodality imaging. A method of treating cancer in a subject comprising administering the nanoprobe and performing photodynamic therapy on the subject is further disclosed.
