Plasmon-Enhanced Fluorescence Near Single Gold Nanoplates Studied by Scanning Near-Field Two-Photon Excitation Microscopy

Abstract

Plasmonic optical fields have been applied for surface-enhanced spectroscopy, chemical sensing, and bioimaging. Spatial distributions of optical fields are critical for optimizing their functionalities. In plasmon-enhanced fluorescence, both incoming and outgoing fields excited by the plasmon should contribute to the enhancement of the fluorescence. Spatial characteristics of plasmons are critical not only for the fundamental understanding of the plasmon but also for their practical applications. Here, we investigate the spatial characteristics of the excitation and relaxation processes near the gold nanoplate using time-resolved near-field two-photon microscopy. We reveal from near-field optical microscopy that the incident field is locally enhanced by the plasmon resonance effect and the lightning rod effect. Near-field time-resolved fluorescence imaging demonstrates that the fluorescence decay is accelerated entirely over the surface of the plate regardless of the spatial distribution of the incident field. These results provide deep insight into plasmonic optical fields and are of great importance for designing plasmon-based substrates for surface-enhanced spectroscopy and photochemical reactions.

Photoluminescence Properties of Gold Nanorod and J-Aggregate Hybrid Systems Studied by Scanning Near-Field Optical Microscopy

“…Next, near-field PL microscopy is carried out to clarify the PL properties of the hybrids. In a previous study, we performed the fluorescence lifetime measurement of dye molecules using the near-field optical microscopy and the confocal microscopy and proved that the near-field probe tip little affects the decay dynamics of the dyes . This fact indicates that the near-field probe tip induces neither PL enhancement nor quenching.…”

“…In a previous study, we performed the fluorescence lifetime measurement of dye molecules using the near-field optical microscopy and the confocal microscopy and proved that the near-field probe tip little affects the decay dynamics of the dyes. 33 This fact indicates that the near-field probe tip induces neither PL enhancement nor quenching. A near-field PL excitation image in the Supporting Information (Figure S3) shows multiple bright spots, indicating that the PL was enhanced at the hybrids.…”

Plate-Like Colloidal Metal Nanoparticles

“…Because the higher-order LSPR modes are nonradiative (also known as “dark modes”), the accessibility of far-field excitation is very limited. On the contrary, near-field microscopic techniques, such as scanning near-field optical microscopy (SNOM), − scanning transmission electron microscopy with EELS, , and CL spectroscopy, can excite the LSPR modes locally and therefore can be used to characterize higher-order LSPR modes. The pioneering work by Stéphan et al opened the possibility of LSPR visualization at high spatial resolution by STEM-EELS measurements, where different LSPR modes of a triangular Ag nanoplate can be selectively excited by a subnanometer electron beam (Figure B) .…”

Selective Excitation of Dark Plasmon Modes Using Cylindrical Vector Beams Studied by Microscopic Imaging of Nonlinear Photoluminescence

“…Tight light confinement is occurred in the vicinity of a structure, resulting in a strongly enhanced optical field. 1,2 The confined optical field significantly enhances optical processes and has been applied to sensing, 3−5 bioimaging, 6,7 fluorescence enhancement, 8,9 surface-enhanced Raman scattering, 10,11 and chemical reactions. 12,13 To utilize the plasmonic fields for these applications, visualization and control of plasmons are indispensable.…”