Figure 1.

(a) Optical absorption spectrum of different tissue types which could be used as endogenous contrast agents in vivo. (b) Exogenous contrast agents such as gold nanospheres (16 nm diameter), silver nanotriangles (200 nm on edge), and gold nanorods (10 nm by 40 nm) and their corresponding extinction spectrum. Tunable peaks show that nanoparticles can be used as contrast agents in various applications.