Metal-enhanced fluorescence (MEF) has been regarded as an emerging tool in fluorescence imaging or sensing due to its brightness and photostability. Fluorophores’ emissions are enhanced by the local field enhancement of the surface plasmon resonance (SPR) of metal surfaces and the plasmon-coupled emission induced by the energy transfer between fluorophores and SPR. However, the details of MEF are not fully understood yet and require further investigation.<br/>In this work, fluorescence enhancements and emission kinetics of fluorophores by the dipole and quadrupole SPR bands of homogeneous silver colloidal films have been investigated by time-resolved fluorescence spectroscopy, where substantial fluorescence enhancements of several fluorophores are observed. The quadrupole SPR of metal nanoparticles has rarely been studied for the MEF due to the difficulties in preparing homogeneous metal nanoparticles large enough to bring strong quadrupole SPR. Moreover, the MEF originating from the plasmon-coupled emission via the energy transfer between the dipole or quadrupole SPR and fluorophores in the excited states will be reported. Lastly, optimization of fluorescence enhancements will be implemented by preparing the composite nanosurfaces which consist of multiple nanoparticles of various SPR properties. For example, significant fluorescence enhancements have been observed with the combination of nanoparticles whose dipole or quadrupole SPR bands are in good spectral overlap with the fluorophores’ emission.

Emission enhancement by dipole and quadrupole surface plasmons of silver nanosurfaces

ACS Fall 2021

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