Metal Nanostructures with Plasmonically Enhanced Raman and Photoluminescence Signals

Authored by: Jeong-Eun Park , Minho Kim , Jiwoong Son , Chungyeon Lee , Sung Min Ko , Jwa-Min Nam

21 Century Nanoscience – A Handbook

Print publication date:  November  2020
Online publication date:  November  2020

Print ISBN: 9780815356417
eBook ISBN: 9780429351617
Adobe ISBN:

10.1201/9780429351617-7

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Abstract

Shrinking light at the nanoscale with plasmonic nanomaterials has yielded numerous intriguing outcomes. In particular, the considerable local field enhancement that arises from the strong light confinement result in significantly improved optical responses such as surface-enhanced Raman scattering (SERS) and metal-enhanced fluorescence (MEF) (Lakowicz 2005, Le Ru and Etchegoin 2012, Dong et al. 2015, Ding et al. 2016, Nam et al. 2016, Park et al., 2017a). SERS is one of the most distinguished and quickly evolving fields. Raman spectroscopy was developed as early as 1928, and this technique involves the inelastic scattering of light and provides information about the molecular structure of chemicals (Raman and Krishnan 1928). It has, however, not been heavily utilized for practical applications because of the small molecular Raman cross section. Since the measurement of the Raman spectra of submonolayer molecules on roughened metal surfaces (Albrecht and Creighton 1977, Jeanmaire and Van Duyne 1977) and the possibility of single-molecule SERS (SMSERS) (Kneipp et al. 1997, Nie and Emory 1997), recent advances have enabled SERS as an effective tool for chemical sensing and bioimaging (Ding et al. 2016, Kumar et al. 2016). When the plasmonic nanostructure couples with fluorophores, the florescence signal increases by plasmonic effect (Drexhage 1974). Recent advances in structural design for proper distance control and flexible modulation of plasmonic resonance to maximize the fluorescence signal allow enhancement factors (EFs) over several thousand times for fluorophores emitting visible light (Punj et al. 2013, Puchkova et al. 2015). Also, infrared (IR)-emitting fluorophores, whose quantum yield is usually very low showed more than one order of magnitude enhancement (Ayala-Orozco et al. 2014). While SERS and MEF are caused by the interaction between molecules and plasmonic nanostructures, the direct emission of light by metals is called photoluminescence (PL). This phenomenon can be divided into two classes: one-photon-induced PL and two-photon-induced PL (Boyd et al. 1986). One-photon PL is a process involving a single photon, while in the other, two photons are sequentially absorbed in the two-photon PL process and photons of higher energy are then emitted (Mooradian 1969, Imura et al. 2005). Recently, plasmonic effects on one-photon PL have attracted increasing attention. Although light emission from metals is much weaker than that from molecular systems because of fast and strong electron–electron interactions and electron–phonon interactions (Hartland 2011), light emission by PL does not undergo photobleaching or photoblinking, and can be further enhanced via molecular and nanostructural engineering, and can therefore be distinguished from the PL of organic dyes or quantum dots.

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