This allows the ability to tune the nanorod absorption from 550nm to 1400nm through different manufacturing processes as shown on the right in Figure 1. This tuning results in the ability of gold nanorods to scatter at wavelengths across the visible and near-IR regions. The surface plasmon resonance (SPR) value is a measure of surface electromagnetic waves that travel in a direction parallel to metal/solvent interface and is heavily influenced by any material that is adsorbed onto the metal surface or to the surface of metal nanoparticles. Very accurate absorption values for metal nanostructures can be achieved by measuring the SPR values at a range of wavelengths (Figure 1).