Gold nanoparticle arrays and gold nanorods produce tunable plasmon responses in the near-infrared (NIR) range and can be used to explore biochemical processes in living systems. Colloidal gold nanoparticles up to 170 nm have been self-assembled into periodic 2D arrays when encapsulated by a novel surfactant (resorcinarene tetrathiol). The arrays are capable of supporting cell adhesion, and can be excellent substrates for surface-enhanced Raman scattering (SERS) at NIR excitations. Spherical "superparticle" ensembles (gold nanoparticles densely packed around submicron silica cores) have also been constructed by self-assembly, and exhibit strong NIR extinction and scattering. These core-shell assemblies have been implanted into live cells as intracellular nanoprobes for detecting chemical influx. Third, gold nanorods can be engineered to have longitudinal plasmon resonances at NIR frequencies, and possess outstanding characteristics as optical contrast agents. Gold nanorods can produce strong two-photon luminescence (TPL), and have been imaged in vivo at the single-particle level while passing through a mouse blood vessel. [DOI: 10.1380/ejssnt.2006.9]