C9413 FCS-Unit for Fluorescence Correlation Spectroscopy

The FCS-Unit is a photometric instrument designed to measure molecular interactions in solution at single molecule level by using fluorescence correlation spectroscopy (FCS).

In contrast to other fluorescence techniques, the parameter of primary interest is not the emission intensity itself, but rather spontaneous intensity fluctuations caused by tiny deviations of the system from thermal equilibrium. These fluctuations can be caused by diffusion of the fluorescent particles in the excitation volume or by a change of fluorescence due to chemical reactions. The time pattern (autocorrelation) of the fluorescence intensity fluctuations can give information about the rate of diffusion of molecules and their concentration in the analysis volume.

The C9413 FCS-Unit consists of four major elements: (1) a LD-pumped low noise solid-state laser to excite fluorescence molecules, (2) a confocal optics to focus the laser beam onto a very small volume of less than one femtolitre, (3) a high sensitive photomultiplier tube with a GaAsP photocathode to detect the fluorescence signal and (4) a digital correlator (installed in a Computer) to perform arithmetic operation and analysis.
FCS is applicable for monitoring a multitude of bio-molecular association and dissociation processes, like protein folding, drug binding, molecular diffusion in the nucleus and cytoplasm, antigen-antibody reaction, DNA-DNA interaction, lateral segregation of lipids in bi-layer membranes, nucleic acid fragmentation and hybridization etc.