Magnetron-sputtered Polytetrafluoroethylene-stabilized Silver Nanoisland Surface for Surface-Enhanced Fluorescence

Area of Science:

• Plasmonics
• Spectroscopy
• Materials Science

Background:

• Surface-enhanced fluorescence (SEF) relies on spectral overlap between fluorophore, nanostructure's localized surface plasmon resonance (LSPR), and excitation wavelength.
• Riboflavin (vitamin B2) is a common fluorophore whose SEF can be modulated by plasmonic nanostructures.

Purpose of the Study:

• To investigate the dependence of SEF intensity and lifetime of riboflavin on spacer layer thickness.
• To determine the effect of spacer-modified silver substrates on riboflavin's fluorescence quantum yield.

Main Methods:

• Fabrication of silver nanoisland substrates coated with varying thicknesses (~5-25 nm) of magnetron-sputtered polytetrafluoroethylene (ms-PTFE) spacer.
• Adsorption of 10 µM riboflavin in DMSO onto the ms-PTFE surface to form a monomolecular layer.
• Microspectroscopic measurements using a sessile droplet method and time-resolved fluorescence.

Main Results:

• SEF intensity and lifetime of riboflavin were monitored with respect to ms-PTFE spacer thickness.
• A 5 nm ms-PTFE layer showed the largest fluorescence enhancement, estimated at 4×.
• Time-resolved fluorescence revealed a 2.3× increase in quantum yield due to shortened radiative decay near the plasmonic surface.

Conclusions:

• Spacer thickness is a critical parameter for optimizing SEF.
• The ms-PTFE spacer effectively modulates the plasmonic enhancement of riboflavin fluorescence.
• The study demonstrates the potential of spacer-modified plasmonic substrates for enhancing fluorescence.