Metal-enhanced single-molecule fluorescence on silver particle monomer and dimer: coupling effect between metal...

Area of Science:

• Nanophotonics
• Single-molecule spectroscopy
• Plasmonics

Background:

• Single-molecule fluorescence is crucial for biological imaging.
• Metal nanoparticles can enhance fluorescence through plasmonic effects.
• Understanding near-field interactions is key to optimizing fluorescence enhancement.

Purpose of the Study:

• To prepare and characterize silver particle dimers with localized single Cy5 molecules.
• To quantify the fluorescence enhancement and lifetime shortening of Cy5 molecules near silver monomers and dimers.
• To investigate the underlying near-field interaction mechanisms using experimental and computational methods.

Main Methods:

• Synthesis of 20 nm silver nanoparticles functionalized with single-stranded oligonucleotides.
• Formation of silver particle dimers via hybridization with double-length oligonucleotides containing single Cy5 molecules.
• Single-molecule fluorescence microscopy and lifetime measurements.
• Finite-difference time-domain (FDTD) calculations for electric field distribution analysis.

Main Results:

• A 7-fold fluorescence enhancement was observed on silver monomers and a 13-fold enhancement on silver dimers compared to free Cy5.
• Fluorescence lifetimes of Cy5 molecules were significantly shortened on both silver monomers and dimers.
• FDTD calculations confirmed the strong electric field enhancement near the metal particles, correlating with experimental observations.

Conclusions:

• Silver particle dimers significantly enhance single-molecule fluorescence through near-field plasmonic interactions.
• The observed fluorescence enhancement and lifetime shortening are consistent with strong coupling between the fluorophore and the metal nanoparticles.
• This work provides insights into designing nanostructures for advanced optical sensing and imaging applications.