Self-Assembly of Synthetic and Biological Polymeric Systems of ...

population of molecules by a very short light pulse, the fluorescence intensity decreases
exponentially with a characteristic time, reflecting the average lifetime of the molecules in the
S1 excited state.
Figure 2.14. Illustration of the vibrational bands in the absorption and fluorescence spectra.
As a consequence of the strong influence of the local environment or surrounding medium on
fluorescence emission, fluorescent molecules are currently used for physicochemical,
biochemical and biological investigation. For example, fluorescence spectroscopy can be
employed as a highly sensitive method for protein analysis. Intrinsic protein fluorescence
deriving from the naturally fluorescent amino acid tryptophan (and to a lesser extent from
tyrosine and phenylalanine) can provide information on the protein conformational structure
and it changes. On the other hand, the use of extrinsic fluorescent dyes offer additional
possibilities for protein characterization, i.e. to monitor their refolding and unfolding
processes, to detect molten globule intermediates, or to characterize protein aggregation and
fibrillation amongst others. For example, the dye 1-anilinonaphthalene-8-sulfonate (ANS) is
hardly fluorescence in aqueous environments but become highly fluorescent in apolar-organic
solvents or upon adsorption to solid phases. Other important dyes for protein characterization
are, for example, Nile Red (used for monitoring protein conformational changes), 9-
(dicyanovinyl)-julolidine (DCVJ, used to probe tubulin structure and the formation of
hydrophobic microdomains along protein aggregation), or Congo Red and Thioflavin T (used to
characterize the extent of -sheet formation along protein fibrillation) (40)(41).
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