Photo-bleaching and photon saturation in flow cytometry

Area of Science:

• Analytical Chemistry
• Biophysics
• Cell Biology

Background:

• Flow cytometry involves high-speed particle analysis through intense light, leading to photon saturation and dye photodegradation.
• Understanding dye photophysics is crucial for accurate measurements and avoiding artifacts in flow cytometry.
• Dye photobleaching can significantly impact data quality and quantitative analysis in biological samples.

Purpose of the Study:

• To experimentally determine photon saturation and photodegradation extent for dyes bound to cell nuclei in flow cytometry.
• To investigate the relationship between photon emission and dye destruction under varying illumination intensities.
• To estimate the excited state and molecular lifetimes of commonly used DNA-binding dyes.

Main Methods:

• Developed experimental procedures to measure photon saturation and photodegradation of Hoechst and propidium iodide in flow cytometry.
• Analyzed dye behavior bound to chromatin under different light intensities.
• Estimated molecular lifetimes based on excitation-relaxation cycles.

Main Results:

• The amount of dye bleached per emitted photon is constant across low and high illumination intensities.
• Photon emission and dye destruction are both driven by single excitation photon absorption.
• Estimated lifetimes: Hoechst 33258 (bound to DNA) ~100 cycles, Propidium Iodide ~200 cycles.

Conclusions:

• Photon saturation and photodegradation are intrinsically linked to single photon absorption events in flow cytometry.
• Optimal illumination conditions differ for photobleaching and non-bleaching dyes.
• An optical setup for high-precision measurements of photobleaching dyes was presented.