Fluorescence Correlation Spectroscopy (FCS
) is a tool that
provides quantitative localized measurements of important physical
parameters including mechanisms of transport, molecular mobilities, and
densities of fluorescently labeled species. In the most basic
configuration, FCS examines the inherent correlations exhibited by the
fluctuating fluorescent signal from labeled molecules as they transition
into and out of a specified excitation volume or area. The dual-color
variation, termed Fluorescence Cross-Correlation Spectroscopy (FCCS
is utilized to probe two species labeled with different fluorophores.
FCCS can extend investigations to the examination of biochemical
reactions between two partners, such as reaction rates, kinetics,
fractions of binding or reacting molecules, and mobilities of a complex
formed between the partners.