Quantification of fluctuations from fluorescence correlation spectroscopy experiments in reaction-diffusion systems.

Area of Science:

• Biophysics
• Chemical Physics
• Physical Chemistry

Background:

• Fluorescence correlation spectroscopy (FCS) is a key technique for measuring diffusion and reaction rates.
• The autocorrelation function (ACF) in FCS analyzes fluorescence fluctuations within a small volume.
• Existing theoretical models often assume independent molecular species and Poisson statistics.

Purpose of the Study:

• To theoretically analyze the ACF of molecule number fluctuations in reaction-diffusion systems without approximations.
• To address discrepancies between theoretical predictions and experimental results regarding ACF total weight.
• To explore the influence of inter-species correlations and finite acquisition times on ACF.

Main Methods:

• Theoretical derivation of the ACF for molecule number fluctuations in a reaction-diffusion system.
• Comparison of theoretical ACFs with experimental data from similar systems.
• Incorporation of variance decomposition and finite acquisition time effects into the theoretical model.

Main Results:

• The derived ACF, under corrected assumptions, depends on multiple system timescales.
• The total weight of the ACF aligns with the variance decomposition formula.
• The study demonstrates that FCS can estimate diffusion coefficients of non-observable species in reaction-diffusion systems.

Conclusions:

• The theoretical framework presented refines FCS analysis for complex reaction-diffusion systems.
• Accurate estimation of diffusion coefficients for all species, observable or not, is achievable with FCS.
• The findings pave the way for advanced experimental designs and data interpretation in biophysical studies.