Analytical Form of the Fluorescence Correlation Spectroscopy Autocorrelation Function in Chemically Reactive Systems

Area of Science:

• Chemical Kinetics
• Physical Chemistry
• Spectroscopy

Background:

• Fluorescence correlation spectroscopy (FCS) measures chemical reaction equilibrium constants and diffusion coefficients.
• Existing analytical models for FCS are limited to reactions much faster or slower than diffusion times.
• Intermediate timescale reactions, where reaction rates are comparable to diffusion times, lack robust analytical descriptions.

Purpose of the Study:

• To develop a new analytical form for the autocorrelation function G(t) in FCS.
• To enable the study of chemical reactions occurring on intermediate timescales.
• To provide a versatile tool for analyzing FCS data across various experimental conditions.

Main Methods:

• Development of a novel analytical form for the G(t) autocorrelation function.
• Application to systems involving reversible binding of fluorescently labeled molecules to macromolecules.
• Analysis of FCS data considering diffusion coefficients, reaction rates, and label brightness variations.

Main Results:

• An analytical form for G(t) applicable to intermediate timescale reactions was derived.
• The method accurately analyzes FCS data for reversible binding reactions.
• The approach is valid even when the fluorescent label's brightness changes upon binding.

Conclusions:

• The new analytical FCS method extends the applicability of FCS to intermediate reaction timescales.
• This provides experimentalists with an easy-to-implement tool for precise determination of equilibrium constants and reaction rates.
• The findings facilitate a deeper understanding of chemical dynamics in complex systems.