Figure 1.
Principle of fluorescence correlation spectroscopy. (a) Individual fluorophores diffusing through the observation volume emit brief bursts of photons. (b) Fluorescence intensity time trace. (c) Fluorescence intensity autocorrelation function. Its amplitude at time 0 scales with the inverse NP concentration; the characteristic decay time, τD, scales with the hydrodynamic radius, RH, of the diffusing NPs.