Major signal increase in fluorescence microscopy through dark-state relaxation

Area of Science:

• Microscopy and imaging science
• Photophysics and photochemistry
• Biophysics

Background:

• Fluorescence microscopy is crucial for biological imaging.
• Molecular dark states, like the triplet state, can reduce fluorescence signal.
• Minimizing dark state occupancy is key to maximizing fluorescence yield.

Purpose of the Study:

• To investigate signal gain in fluorescence microscopy by controlling molecular dark state relaxation.
• To determine the impact of temporal pulse separation on fluorescence yield and photobleaching.

Main Methods:

• Utilizing pulsed illumination with temporal separation greater than 1 microsecond.
• Comparing signal gain under one- and two-photon excitation.
• Employing Green Fluorescent Protein (GFP) and Rhodamine dye Atto532 as model systems.

Main Results:

• Observed a 5-25 fold increase in total fluorescence yield before photobleaching.
• Demonstrated signal gain by allowing triplet state relaxation between absorption events.
• Confirmed signal enhancement for both one- and two-photon excitation modalities.

Conclusions:

• Ensuring dark state relaxation significantly boosts fluorescence signal in microscopy.
• This approach enables imaging with reduced photobleaching and higher fluorescence fluxes.
• The findings represent a significant advancement for high-performance fluorescence imaging.