Enhanced single-molecule spectroscopy in highly confined optical fields: from λ/2-Fabry–Pérot resonators to plasmonic nano-antennas

Abstract

While single-molecule fluorescence from emitters with high quantum efficiencies such as organic dye molecules can easily be detected by modern apparatus, many less efficient emission processes such as Raman scattering and metal luminescence require dramatic enhancement to exceed the single-particle detection limit. This enhancement can be achieved using resonant optical systems such as plasmonic particles or nanoantennas, the study of which has led to substantial progress in understanding the interaction of quantum emitters with their electromagnetic environment. This review is focused on the advances in measurement techniques and potential applications enabled by a deeper understanding of fundamental optical interaction processes occurring between single quantum systems on the nanoscale. While the affected phenomena are numerous, including molecular fluorescence and also exciton luminescence and Raman scattering, the interaction itself can often be described from a unified point of view. Starting from a single underlying model, this work elucidates the dramatic enhancement potential of plasmonic tips and nanoparticles and also the more deterministic influence of a Fabry-Pérot microresonator. With the extensive knowledge of the radiative behavior of a quantum system, insight can be gained into nonradiative factors as well, such as energy transfer phenomena or spatial and chemical configurations in single molecules.

Strong and Coherent Coupling of a Plasmonic Nanoparticle to a Subwavelength Fabry–Pérot Resonator

“…10−12 This coupling regime is characterized by energy-level anticrossing, energy shifts, and altered damping rates of the coupled system. Here, we experimentally demonstrate and theoretically analyze strong coupling between the long-axis plasmon oscillation of a single gold nanorod (GNR), dephasing within ∼10−15 fs, and a tunable λ/2-resonator, 13 displayed in Figure 1a, with a Q-factor of ∼30−40 (T 2 ≈ 30 fs) consisting of silver mirrors that are separated by half a wavelength in the visible regime.…”

Wavelength dependent specific plasmon resonance coupling of single silver nanoparticles with EGFP

“…3–13 The coupling of the enhanced electromagnetic field on single Ag NPs with nearby excited states of fluorophore offers an important model to study nanoscale energy transfer for better understanding of their fundamental mechanisms and study of long-range molecular interactions, far beyond 10 nm distance limited by F_rster resonance energy transfer (FRET). 6, 8 …”

Single-site surface-enhanced Raman scattering beyond spectroscopy

“…The increased scattering intensity of the non-totally symmetric mode needs further explanation for the effective resonance process due to the excitation [44]. The possibility of the modulation of the selection rules of the optical absorption process at a highly localized electromagnetic field with a steep gradient of the field intensity has been pointed out [3]. This effect could contribute to increments in the scattering intensity of the non-totally symmetric mode of the system.…”

“…Thus, the use of a metal sharp tip with the scanning microscopy technique for SERS, named tip-enhanced Raman scattering (TERS), has been developed to control the localization of the field. After the findings regarding the modification of the fluorescence lifetime of molecules in the vicinity of a scanning probe microscope tip [21], a specially resolved TERS observation was developed [3,22]. The lateral resolution drastically improved from <100 nm of the initial studies down to the current single-molecule scale [23,24].…”

“…The ability to modify the lightmatter interaction can lead to the fabrication of more effective photoenergy conversion devices. Recently, plasmonics has been developed as a novel way to control light [2,3]. The photoillumination of a small metal nanostructure results in the excitation of a localized surface plasmon resonance (LSPR).…”