Nanostructures, methods of preparing nanostructures, methods of detecting targets in subjects, and methods of treating diseases in subjects, are disclosed. An embodiment, among others, of the nanostructure includes a metallic gold surface-enhanced Raman scattering nanoparticle, a Raman reporter and a protection structure. The protection structure may include a thiol-polyethylene glycol to which may be attached a target-specific probe.