Scanning fluorescence correlation spectroscopy. I. Theory and simulation of aggregation measurements.

Scanning Fluorescence Correlation Spectroscopy (S-FCS) is introduced as an adaptation of Fluorescence Correlation Spectroscopy (FCS) to measure aggregation in systems, such as biological cell membranes, where diffusion or flow is slow. The theoretical framework for interpretation of S-FCS measurements are discussed in this paper with emphasis on the limitations arising from the sample size and shape. Computer simulations of the experiment demonstrate the potential of the technique and illustrate how some of the limitations may be overcome.