Acridine orange interaction with DNA: Effect of ionic strength.

Area of Science:

• Photochemistry
• Biophysics
• Molecular Spectroscopy

Background:

• Acridine orange (AO) is a fluorescent dye used in various applications.
• Understanding AO's spectral characteristics and excited state behavior is crucial for optimizing its use.
• The interaction of AO with DNA and its susceptibility to quenching by radicals like TEMPO are key areas of investigation.

Purpose of the Study:

• To investigate the spectral characteristics of acridine orange (AO).
• To study the quenching of AO's singlet and triplet excited states by TEMPO radical.
• To determine the influence of DNA concentration and NaCl presence on these interactions and AO's binding to DNA.

Main Methods:

• Steady-state and time-resolved optical absorption and fluorescence spectroscopy.
• Fluorescence correlation spectroscopy (FCS).
• Resonant light scattering techniques.

Main Results:

• Demonstrated the equilibrium of AO monomers and aggregates bound to DNA, dependent on concentrations.
• Observed protection of AO monomers at high DNA concentrations, reducing excited state quenching.
• Showed that NaCl addition decreases AO binding to DNA and reduces aggregation.

Conclusions:

• AO-DNA interaction involves complex aggregation/disaggregation, altering AO's spectral properties and accessibility.
• Salt attenuates DNA's influence on AO excited states and efficacy.
• Photosensitizer efficacy can be modulated by DNA interactions, with salt offering a means to control these effects.