Screening nanorods coated with a mixture of SERS active molecules and biocompatible polymer identifies three formulations that may be uniquely distinguished in vivo over a spectral bandwidth of only 6 nm in the near-infrared (a spectral multiplexing density over an order of magnitude greater than attainable with semiconductor quantum dots, organic fluorochromes, and Raleigh scattering nanoparticle imaging approaches), while providing intense photothermal heating for cancer therapy. [GRAPHICS] .