Fluorescence is a central technology in medical testing, drug discovery, biotechnology and imaging. In almost all uses of fluorescence, the fluorophores are in the free-space condition, in which they radiate energy with minimal interactions with their surroundings. Fluorophore interactions with the local environment affect nonradiative decay processes such as quenching, but do not alter the intrinsic rate of radiative decay.Remarkably, proximity of fluorophores to metallic particles can dramatically alter their fluorescence spectral properties in ways that increase quantum yield and photostability, and improve detectability…