Single Molecule Techniques

Fluorescence Correlation Spectroscopy. Petra Schwille and Elke Haustein. Previously published in Biophysics Textbook Online (BTOL).

http://www.biophysics.org/education/schwille.pdf

Optical Tweezers: Measuring Piconewton Forces. Mark Williams. Previously published in Biophysics Textbook Online (BTOL).

http://www.biophysics.org/education/williams.pdf

A Brief Description of Fluorescence Correlation Spectroscopy

What Does FCS Measure?
Fluorescence correlation spectroscopy (FCS) is a single-molecule detection technique that detects and correlates fluctuations in fluorescence intensity within a very small detection volume (on the order of femtoliters).

What Information Do FCS Data Provide?
Concentration
Because the fluorescence intensity inside the femtoliter detection volume is directly related to the number of fluorescent particles, FCS provides a sensitive measure of concentration down to picoMolar values.

Particle Size
By correlating the rate of fluctuations in the concentration within the detection volume, FCS also provides a measure of the rate of diffusion of particles in and out of the detection volume, which is directly related to the size of the particles.

What are the Applications of FCS?
By measuring changes in concentration and size, it's possible to monitor interactions and complexing between macromolecules such as proteins and polynucleic acids on the single-molecule scale. Basically, many of the things that you would use PCR or ELISA to detect, FCS can measure without amplification or washing.

More Information
For more information on FCS theory and applications:
FCS Classroom