Fluorescence Correlation Spectroscopy: Past, Present, Future Elliot L. Elson  Biophysical Journal  Volume 101, Issue 12, Pages 2855-2870 (December 2011) DOI: 10.1016/j.bpj.2011.11.012 Copyright © 2011 Biophysical Society Terms and Conditions

Figure 1 Illustration of the application of PCH and FCS to an aggregating system. (A) Experimental PCH measurements fit to a two-component model system. These data are from a preparation of allophycocyanin trimers from the thermophilic cyanobacterium Thermosynechococcus vulcanus (sample from Liron David and Robert Blankenship). Data were binned at 200 μs. (Solid curve) Best fit of the data to a two-component system that yields the number and brightness of each of the components: N1 = 23.4 ± 0.3, q1 = 4100 ± 60 s−1; N2 = 0.06 ± 0.003, q2 = 65000 ± 1400 s−1. (Dashed and dotted curves) One-component PCH curves calculated for the dimmer and brighter components, respectively. (B) Fluorescence fluctuation autocorrelation function for the sample shown in panel A. The data are compared to two theoretical curves that are virtually indistinguishable. One is a two-component, unconstrained fit (first line in table inset), and the second curve has fixed diffusion times in a ratio of 2.5:1.0, which is the cube root of the brightness ratio in the PCH. The errors are provided by the ConfoCor software (Carl Zeiss Microimaging, Jena, Germany); these are presumably the asymptotic standard errors. N is the number of fluorescent particles in the sample volume; τ1 and τ2 are the diffusion correlation times for the two components; and F1 is the fraction of the correlation function amplitude assigned to component 1. (Both curves have triplet components with approximately the same correlation time and amplitude fraction; not shown.) Biophysical Journal 2011 101, 2855-2870DOI: (10.1016/j.bpj.2011.11.012) Copyright © 2011 Biophysical Society Terms and Conditions