Quantum energy flow macromolecules

Another related phenomenon that results in a lower quantum yield than expected is called concentration quenching. This can occur when a macromolecule, such as an antibody, is heavily labeled with a fluorophore, such as fluorescein isothiocyanate. When this compound is excited, the fluorescence labels are in such close proximity that radiationless energy transfer occurs. Thus, the resulting fluorescence is much lower than expected for the concentration of the label. This is a common problem in flow cytometry and laser-induced fluorescence when attempting to enhance detection sensitivity by increasing the density of the fluorescing label. 

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