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A straightforward STED-background corrected fitting model for unbiased STED-FCS analyses
Wang, R., Brustlein, S., Mailfert, S., Fabre, R., Fallet, M., Sivankutty, S., ... & Marguet, D.
Fluorescence correlation spectroscopy, Stimulated emission depletion, Fluorescence auto-correlation fitting mode, lnon-Gaussian-shaped PSF
Combining stimulated emission depletion and fluorescence correlation spectroscopy (STED-FCS) provides a powerful and sensitive tool for studying the molecular dynamics in live cells with high spatio-temporal resolution. STED-FCS gives access to molecular diffusion characteristic at the nanoscale occurring within short period of times. However due to the incomplete suppression of fluorescence in the STED process, the STED-FCS point spread function (PSF) deviates from a Gaussian shape and challenges the analysis of the auto-correlation curves obtained by FCS. Here, we model the effect of the incomplete fluorescence suppression in STED-FCS experiments and propose a new fitting model improving the accuracy of the diffusion times and average molecule numbers measurements. The implementation of a STED module with pulsed laser source on a commercial confocal/FCS microscope allowed us to apply the STED-background corrected model to fit the STED-FCS measurements. The experimental results are in good accordance with the theoretical analysis both for the number of molecules and the diffusion time which decrease accordingly with the STED power.