The synthesis, magnetic characterization, and optical properties of nanoparticles with iron oxide cores and gold shells are presented. The nanoparticles are superparamagnetic at room temperature and can be reversibly collected by a permanent magnet. They display a localized surface plasmon resonance peak at 605 nm, and their large scattering cross-section allows them to be individually resolved in darkfield optical microscopy as they undergo Brownian motion in aqueous suspension.