title: Dual-focus fluorescence correlation spectroscopy.
abstract: This chapter introduces into the technique of dual-focus fluorescence correlation spectroscopy or 2fFCS. In 2fFCS, the fluorescence signals generated in two laterally shifted but overlapping focal regions are auto- and crosscorrelated. The resulting correlation curves are then used to determine diffusion coefficients of fluorescent molecules or particles in solutions or membranes. Moreover, the technique can also be used for noninvasively measuring flow-velocity profiles in three dimensions. Because the distance between the focal regions is precisely known and not changed by most optical aberrations, this provides an accurate and immutable external length scale for determining diffusivities and velocities, making 2fFCS the method of choice for accurately measuring absolute values of these quantities at pico- to nanomolar concentration.
authors.affiliation: Third Institute of Physics-Biophysics, Georg-August-University Göttingen, Göttingen, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Pieper
authors.forename: Kerstin
authors.initials: K
authors.lastname: Weiß
authors.forename: Ingo
authors.initials: I
authors.lastname: Gregor
authors.forename: Jörg
authors.initials: J
authors.lastname: Enderlein
mesh_terms: D000465:Algorithms; D002138:Calibration; D008051:Lipid Bilayers; D013050:Spectrometry, Fluorescence / Q000379:methods*
chemical_list: D008051:Lipid Bilayers