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Compact FCS and FCCS instrument
Fluctuation Dual Emission Uni-laser eXcitation

Interaction analysis in solution

FlucDEUX™ is a compact FCS and single wavelength laser FCCS instrument. In combination with normal green fluorescent dyes (Azami-Green1, Alexa488) and large Stokes shift dyes such as Keima or quantum dots, both dyes can be excited with a single wavelength laser at the same confocal volume and at the same time, without interference between the fluorescence of the dyes(no FRET, no cross talk). This system is more sensitive and simpler than the generally used two wavelength laser FCCS.

FCS, FCCS read-out parameters

• Number of molecules ⇒ Concentration
• Diffusion times ⇒ Molecule size, interaction
• Fraction of components ⇒ Bound/free ratio
• Cross-correlation⇒ Interaction of two species


• Detection of Proteolysis
• On and Off Interaction

What are FCS and FCCS?

Fluorescence Correlation Spectroscopy (FCS) is a highly sensitive and specific optical technique for the study of molecular interactions in solution. FCS monitors the fluctuations in fluorescent intensity caused by the random in and out migration of fluorescently labeled molecules in the conforcal area. From these fluctuations, FCS provides information on the rate of diffusion of molecules and their concentration in the analysis volume. Because small molecules diffuse more rapidly than large molecules, an interaction between two molecules detected as the increase in the particle's diffusion time. However, FCS has limitations in its ability to distinguish between different particles and can do so only if the diffusion times differs. The diffusion time is proportional to the cubic root of the mass, and so particles with a mass difference of a factor less than eight cannot be distinguished. In this case the more sensitive FCCS is recommended because in principle, it detects interactions between particles of similar mass.

Fluorescence Cross-Correlation Spectroscopy(FCCS) is an extended version of FCS. With FCCS, two spectrally distinct fluorophores are used to label two species to study their interactions. If the differently labeled particles are interacting, they diffuse through the conforcal area in a synchronized manner, inducing simultaneous fluctuations of the fluorescence intensities in the two color channels, and thus a positive cross-correlation readout.

Software Interface


1:Detection of the Ca2+-dependent Association between CaM and M13 Peptide with FCCS
2:Detection of Proteolysis Using FCCS