Two-photon fluorescence lifetime for label-free microfluidic droplet sorting.

Area of Science:

• Microfluidics
• Analytical Chemistry
• Biotechnology

Background:

• Current microfluidic droplet sorting relies on fluorescence detection, requiring pre-labeling and limiting applications.
• Label-free detection methods are highly sought after for broader applicability in microfluidic systems.

Purpose of the Study:

• To develop and demonstrate a label-free droplet sorting system using time-resolved two-photon excitation (TPE) fluorescence detection.
• To enable the detection and sorting of small aromatic compounds and biological entities without prior labeling.

Main Methods:

• Utilized time-resolved two-photon excitation (TPE) fluorescence detection with excitation at 532 nm.
• Employed time-correlated single-photon counting (TCSPC) to differentiate compounds based on fluorescence lifetimes.
• Developed a polydimethylsiloxane-fused silica (FS) hybrid microfluidic chip for deep-UV optical transparency and droplet handling.
• Integrated a 532-nm picosecond laser and a chip-integrated dielectrophoretic pulsed actuator for sorting.

Main Results:

• Successfully demonstrated label-free detection of small aromatic compounds absorbing in the deep-UV region.
• Achieved sorting of droplets containing serotonin or propranolol based on their distinct fluorescence lifetimes.
• Showcased the platform's utility in screening yeast cells by analyzing protein autofluorescence via TPE fluorescence lifetime.

Conclusions:

• Time-resolved TPE fluorescence detection offers a powerful label-free approach for droplet microfluidics.
• The developed hybrid chip and integrated system enable precise sorting of molecules and cells based on intrinsic fluorescence properties.
• This technology expands the capabilities of microfluidic systems for chemical analysis and biological screening.