mEos4b Photoconversion Efficiency Depends on Laser Illumination Conditions Used in PALM

Area of Science:

• Biophysics
• Microscopy
• Molecular Biology

Background:

• Green-to-red photoconvertible fluorescent proteins (PCFPs) are crucial for photoactivated localization microscopy (PALM).
• Their complex photophysics, including limited photoconversion efficiency (PCE), hinders spatial resolution and quantitative accuracy in PALM.
• Understanding PCFP photophysics is essential for optimizing super-resolution imaging techniques.

Purpose of the Study:

• To investigate the factors influencing the photoconversion efficiency (PCE) of the mEos4b PCFP.
• To determine the impact of illumination conditions on mEos4b PCE and its implications for PALM.
• To develop a refined photophysical model explaining mEos4b behavior.

Main Methods:

• Experimental manipulation of illumination conditions (488 nm and 405 nm light) for mEos4b.
• Photophysical characterization of mEos4b under varied light exposures.
• Development and validation of a refined photophysical model for mEos4b.

Main Results:

• The PCE of mEos4b is not a constant but varies significantly with illumination parameters.
• Applying 488 nm light to reduce blinking in red mEos4b decreases its PCE.
• mEos4b PCE is strongly dependent on the power density of the 405 nm illumination.
• A new model explains these effects via nonlinear green-state photobleaching involving a radical dark state.

Conclusions:

• Illumination conditions critically control the PCE of mEos4b, a key factor for PALM.
• Optimizing illumination strategies can potentially improve PCE and overcome limitations in PALM resolution and quantification.
• The refined photophysical model provides deeper insights into PCFP behavior, aiding future probe development.