Question

Please compare and contrast intrinsic versus extrinsic fluorophores. Please be sure to clearly address differences in terms of quantum yield, fluorescence lifetimes, cost, etc.

Answer 1

Fluorophores are typically polyaromatic compounds having a conjugated π-electron system. Fluorophores in biological applications can be broadly divided into two main categories: intrinsic and extrinsic. Intrinsic fluorophores are the ones that occur naturally and include aromatic amino acids, nicotinamide adenine dinucleotide (NADH), flavins, and derivatives of pyridoxal and chlorophyll.

Most intrinsic fluorophores require excitation by short wavelength ultraviolet and blue light which is often hazardous for live cells. Further, the brightness and quantum yield of intrinsic fluorophores is, in general, quite low for most practical applications. The amino acid tryptophan has the strongest fluorescence quantum yield of the amino acids found in proteins. The rest either do not fluoresce or fluoresce weakly. Therefore "Intrinsic Protein Fluorescence" usually refers to the fluorescence emission of the tryptophan amino acids.

Extrinsic fluorophores are added to the sample to provide fluorescence when none exists, or to change the spectral properties of the sample. Extrinsic fluorophores include dansyl, fluorescein, rho-damine, and numerous other substances.

Ability to tune the wavelengths and intensities of
absorption and emission of fluorophores will add to the range of properties that are currently available, and will increase their
utility and range of applications.