Fluorescence cross-correlation spectroscopy
Fluorescence cross-correlation spectroscopy (FCCS) is a spectroscopic technique that examines the interactions of fluorescent particles of different colours as they randomly diffuse through a microscopic detection volume over time, under steady conditions. == Discovery == Eigen and Rigler first introduced the fluorescence cross-correlation spectroscopy (FCCS) method in 1994.
Source: Wikipedia — Fluorescence cross-correlation spectroscopy (CC BY-SA 4.0)