Extracting decay curves of the correlated fluorescence photons measured in fluorescence correlation spectroscopy

We have developed a new method to extract the decay curves of the correlated fluorescence photons from the data of fluorescence correlation spectroscopy using time-correlated single photon counting. In this method, a two-dimensional correlation map of photon pairs is generated at an absolute delay time with reference to the excitation-emission delay of each photon. Using a dye-labeled DNA as an example, we have demonstrated that the decay curve of the correlated fluorescence photons is separated from the uncorrelated background signals simply by subtracting a two-dimensional correlation map at sufficiently long delay time without additional prior information.