Single metal nanoparticles: optical detection, spectroscopy and applications

Since the first report on the far-field optical detection of single metal nanoparticles in the late 1990s, the field has rapidly developed and new methods and concepts have been introduced. Eliminating averaging over the broad size, shape and crystallinity distributions produced by even the best of current synthesis methods, these techniques have proven extremely useful for gaining a deeper insight into many of the properties of metal nanoparticles. These techniques have already led to the first applications specifically directed at using single particles. In this review we describe far-field optical techniques (both linear and nonlinear) that have sufficient sensitivity to detect single metal particles. We further discuss emerging applications, and emphasize the importance of single-particle detection techniques in their development.