Fluorescence Detection of Single DNA Molecules

Area of Science:

• Biophysics
• Molecular Biology
• Nanotechnology

Background:

• Single-molecule detection (SMD) and single-molecule fluorescence resonance energy transfer (smFRET) are crucial techniques for studying molecular dynamics.
• Previous studies have faced challenges in achieving high signal-to-noise ratios and accurate measurements in complex systems.

Purpose of the Study:

• To develop and validate robust methods for single-molecule detection and smFRET analysis of DNA molecules.
• To compare the performance of smFRET in immobilized substrate systems versus microdroplet environments.
• To accurately measure FRET efficiency and inter-dye distances for single DNA molecules.

Main Methods:

• Utilized Cy3- and Cy5-labeled single-strand DNAs (ssDNAs) for fluorescence labeling.
• Employed total internal reflection fluorescence microscopy (TIRFM) for high-quality imaging.
• Investigated both substrate-immobilized ssDNAs (via electrostatic adsorption) and ssDNAs encapsulated in microdroplets within T-type microfluidics.

Main Results:

• Achieved high signal-to-noise ratios (mean S/N = 6.9 ± 0.34) for single molecules immobilized on substrates.
• Successfully detected single and double fluorophore-labeled DNA molecules within microdroplets.
• Accurately measured FRET efficiency and inter-dye distances for single donor-acceptor pairs in the microdroplet system.

Conclusions:

• Both substrate immobilization and microdroplet encapsulation are effective strategies for single-molecule analysis using smFRET.
• The microdroplet system offers a novel platform for detailed smFRET analysis, including in complex microfluidic channels.
• This work advances the capabilities for precise characterization of individual biomolecules.