Figure 3.

Detecting interactions with two-color FCS. Simulations of two-color FCS experiments were run considering two populations of molecules tagged with spectrally separated fluorescent probes (depicted as red circles and green rectangles). The fluorescence intensity of these molecules was assumed to be collected in independent channels (red and green symbols, respectively). (A–D) The ACFs of the intensity obtained for the red (○) and green (□) channels, and the CCFs (gray symbols) were calculated for the following scenarios: (A) noncompetitive binding, (B) competitive binding, (C) complex formation and binding, and (D) sequential binding. The diffusion and binding model proposed by Michelman-Ribeiro et al. (13) was fitted to the ACF and CCF curves in those scenarios in which the assumptions of the model were fulfilled (continuous lines). The simulated and recovered parameters are summarized in Table S1. To see this figure in color, go online.