Figure 1: (a) Scanning electron microscope images of a few of the commercial Au colloidal particles. Scale bar is 60  m. (b) Composite SEM image of “developed” gold-silver core-shell colloidal particles. Ag layer varies from a few nm to a few 10s of nm in thickness, resulting in sizes varying from 70 to 150 nm. Scale bar is 100  m. (c) Schematic of the targeted nanosensor. Au@Ag nanoparticle with DNP and 4-MPy ligands, not drawn to scale. (a and b) Reprinted with permission from Nowak-Lovato et al. [11] (copyright 2009 Society for Applied Spectroscopy).