Fluorescence relaxation dynamics of acridine orange in nanosized micellar systems and DNA

In this paper, we report a detailed study of the fluorescence relaxation dynamics of a well-known fluorescent DNA intercalator, acridine orange (AO), in reverse micelles (RM), micelles, and DNA using picosecond resolved fluorescence spectroscopy. Solvation studies of AO in AOT reverse micelles (RM) containing water indicate the locations of AO close to the interface and those in RM containing NaOH; there are two types of AO--one in the nonpolar oil phase and the other at the interface. The bound water at the reverse micellar interface is found to be much more rigid than that at the micellar interface of sodium dodecyl sulfate (SDS) micelles. Dynamic light scattering (DLS) studies allow for the determination of the hydrodynamic radius and the overall tumbling motion of the macromolecules. Wobbling-in-cone data analysis of the temporal fluorescence anisotropy decay allows for determination of restriction on the motion of fluorophores attached to the macromolecules. This model further applied to AO-intercalated genomic DNA and synthetic oligonucleotides within their structural integrity (as confirmed through circular dichroism (CD) studies) shows that AO experiences less restriction in genomic salmon sperm DNA compared with that in synthetic oligonucleotides, and among the oligonucleotides, the ones with AT base pairs are much more rigid. This study would invoke further research on the dynamical nature of AO in restricted environments.