Fluorescence Photon Correlation
In 1904 Smoluchowski derived1 that the number N of particles in an open volume — i.e. one defined by optical beam geometry, not by mechanical walls — shows fluctuations δN the relative deviation of which is σN/No = No −1/2. As a consequence the fluctuations are discernible only if No is small. Verification of this by meticulous observations under a microscope is due to Svedberg who also coined the term paucimolecular phenomena2. The phenomenon has been rediscovered in dynamic light scattering where it was referred to as occupation number fluctuations3. Recently, Magde, Elson, and Webb7,8 combined the number fluctuation concept with analog fluorescence autocorrelation4,5 into what they called concentration correlation spectroscopy.
KeywordsOpen Volume Solute Molecule Rayleigh Scattering Mechanical Wall Dark Count Rate
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