Dark State-Modulated Fluorescence Correlation Spectroscopy for Quantitative Signal Recovery

Area of Science:

• Nanophotonics and Spectroscopy
• Biophysical Chemistry

Background:

• Few-atom silver (Ag) clusters exhibit fluorescence with significant dark state populations.
• Strong background emission in biological samples complicates fluorescence detection and analysis.

Purpose of the Study:

• To develop a method for dynamically removing background noise in fluorescence measurements.
• To enable quantitative analysis of silver nanodot fluorescence in high-background environments.

Main Methods:

• Utilized modulated dual-laser fluorescence correlation spectroscopy (FCS).
• Employed long-wavelength coillumination to optically depopulate dark states and modulate nanodot fluorescence.
• Applied correlation-based averaging to remove unmodulated background.

Main Results:

• Achieved dynamic optical depopulation of dark states, enabling modulation of nanodot fluorescence without affecting background.
• Successfully recovered pure Ag nanodot fluorescence correlations even with spectrally overlapping background emission.
• Demonstrated linear fluorescence recovery with Fourier amplitude, providing background-free quantitation.

Conclusions:

• Modulated dual-laser FCS is an effective method for background suppression in fluorescence spectroscopy.
• This technique facilitates the study of modulatable fluorophores in complex biological samples and multiplexed assays.
• Enables quantitative analysis of emitter concentration in challenging, high-background environments.