Associated anisotropy decays of Ethidium Bromide interacting with DNA

Rahul Chib, Sangram Raut, Sarika Sabnis, Preeti Singhal, Zygmunt Gryczynski, Ignacy Gryczynski

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Ethidium Bromide (EB) is a commonly used dye in a deoxyribonucleic acid (DNA) study. Upon an intercalation, this dye significantly increases its brightness and fluorescence lifetime. In this report we have studied the time resolved fluorescence properties of EB existing simultaneously in free and DNAbound forms in the solution. Fluorescence intensity decays were fitted globally to a double exponential model with lifetimes corresponding to free (1.6 ns) and bound (22 ns) forms, and molar fractions were determined for all used solutions. Anisotropy decays displayed characteristic time dependence with an initial rapid decline followed by recovery and slow decay. The shortlived fraction associated with free EB molecules decreases faster than longlived fraction associated with EB bound to DNA. Consequently, contribution from fast rotation leads to initial rapid decay in anisotropy. On the other hand bound fraction, due to slow rotation helps recover anisotropy in time. This effect of associated anisotropy decays in systems such as EB free/EB-DNA is clearly visible in a wide range of concentrations, and should be taken into account in polarization assays and biomolecule dynamics studies.

Original languageEnglish
Article number015003
JournalMethods and Applications in Fluorescence
Issue number1
StatePublished - Mar 2014


  • Associated anisotropy decays
  • DNA fluorescence
  • Ethidium bromide


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