FCSXpert Solutions: Fluorescence Correlation Spectroscopy Simplified!.
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FCS Classroom

What is FCS?

Fluorescence correlation spectroscopy (FCS) is a powerful single-molecule detection technique that measures and correlates fluctuations in fluorescence intensity within a very small detection volume (on the order of femtoliters). This section introduces the physical processes and mathematical theory that govern FCS.

Representation of confocal volume
Creating the very small detection volume:
Correlating fluorescence intensity fluctuations:
Causes of fluorescence intensity fluctuations:

For detailed derivations of mathematical equations used to describe FCS, please see Mathematics of Autocorrelation.