Fluorescence in colloidal solutions: Scattering vs physicochemical effects on line shape

Area of Science:

• Photophysics
• Spectroscopy
• Materials Science

Background:

• Fluorescence spectroscopy is a powerful tool for probing molecular environments.
• Understanding dye-molecule interactions in complex media is crucial for various applications.
• Scattering effects can complicate spectral analysis, but their impact on line shape needs clarification.

Purpose of the Study:

• To investigate the influence of different particle suspensions on the fluorescence line shapes of fluorescein and laurdan.
• To differentiate the effects of scattering from physicochemical interactions on spectral line shapes.
• To establish line shape analysis as a sensitive method for studying dye-particle interactions.

Main Methods:

• Fluorescence spectroscopy was used to analyze fluorescein and laurdan in various suspensions, including polystyrene nanoparticles (PSNP), anionic/cationic micelles, and lipid vesicles.
• Spectra were deconvoluted using Gaussian (fluorescein) and lognormal (laurdan) distributions.
• Line parameters were analyzed in relation to particle concentration and physicochemical effects.

Main Results:

• Scattering primarily affected fluorescence intensity, not line shape.
• Physicochemical interactions, such as dye-micelle or dye-nanoparticle binding, significantly altered line width and peak position.
• Fluorescein showed pH-dependent shifts in anionic systems, while interacting with cationic micelles and PSNP.
• Laurdan indicated decreasing polarity in lipid vesicles with increasing lipid concentration.

Conclusions:

• Fluorescence line shape analysis is a more sensitive indicator of molecular interactions than intensity alone.
• Physicochemical interactions dominate spectral line shape modifications, overriding scattering effects.
• This approach provides valuable insights into dye behavior in complex colloidal systems.