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S. E. H. Murph and E. Searles
as Raman scattering. Through employing the fingerprint capabilities of Raman scattering, an advantageous spectroscopy technique can be employed to provide distinctive data to reveal the identity of the analyte. The main obstacle facing this form of
analysis is the intensity of the Raman scattering signal [2]. Due to the low-intensity
scattering signal of the not forbidden but rare occurrence of inelastic collisions during
the introduction of incident light, a technique was developed to enhance the signature
spectra of interrogated chemicals.
Surface-enhanced Raman spectroscopy (SERS) is a surface-sensitive analytical
technique that enhances Raman scattering of chemical species adsorbed on rough
surfaces or nanoscale structures [1–3]. This technique is used to observe vibrational,
rotational, and other low-frequency modes in a system. It provides a structural fingerprint by which molecules can be identified. There are two mechanisms to describe the
overall SERS enhancement effect: the electromagnetic (EM) and chemical (CHEM)
enhancement mechanisms. Electromagnetic enhancement is due to the increased
local electric field incident on an adsorbed molecule at a metallic surface, due to
visible light absorption by the metal. Chemical enhancement results from electronic
resonance/charge transfer between a molecule and a metal surface, which leads to
an increase in the polarizability of the molecule [3–5].
The Raman enhancement technique was first observed by Fleischmann’s group
on the surface of a silver electrode [2]. This enhancement response was due to the
interaction of the rough metal surface leading to the increase of the inelastic collision signal [2]. The presence of the metal surface roughness increased the scattering
effect and led to better sensitivity [2]. Surface-enhanced Raman spectroscopy is a
growing chemical field due the recent advances in the nanoscience and nanotechnology fields. Enhancements of 10
6 are often claimed and higher values are seen
in specific instances [4–7]. Even single molecule detection was reported by several
groups when employing nanoscale materials [8].
Nanoparticles with large surface area and unique characteristics that are distinct
from their bulk material provide an attractive possibility for exploring the enhancement of inelastic scattering signal [8]. Surface-enhanced Raman spectroscopy
(SERS) has been explored through using nanoparticles to increase the Raman signal
for sensing, bioanalysis, catalytic analysis, and environmental applications [2, 4, 8,
9] (Fig. 1).
In metal nanoparticles, namely gold and silver nanoparticles, “plasma oscillations”, which are collective oscillation of electrons, driven by external electromagnetic fields are localized and lead to strong resonances at specific wavelengths that
are dependent on the particle size, shape, and the local dielectric environment [4,
7]. Localized surface plasmon resonance (LSPR) has the greatest contribution to
surface-enhanced Raman spectroscopy (SERS) as electrons oscillate at nanoparticle
surfaces [3–8].
Gold and silver nanoparticles have been widely used for applications in surfaceenhanced Raman spectroscopy (SERS) studies because of their unique properties
[3–6]. They are highly stable, and their plasmonic properties occur in the visiblenear IR range allowing the optical properties to be easily controlled and monitored
[4, 6, 10]. In the previous research, it has been found that bimetallic silver–gold
S. E. H. Murph and E. Searles
as Raman scattering. Through employing the fingerprint capabilities of Raman scattering, an advantageous spectroscopy technique can be employed to provide distinctive data to reveal the identity of the analyte. The main obstacle facing this form of
analysis is the intensity of the Raman scattering signal [2]. Due to the low-intensity
scattering signal of the not forbidden but rare occurrence of inelastic collisions during
the introduction of incident light, a technique was developed to enhance the signature
spectra of interrogated chemicals.
Surface-enhanced Raman spectroscopy (SERS) is a surface-sensitive analytical
technique that enhances Raman scattering of chemical species adsorbed on rough
surfaces or nanoscale structures [1–3]. This technique is used to observe vibrational,
rotational, and other low-frequency modes in a system. It provides a structural fingerprint by which molecules can be identified. There are two mechanisms to describe the
overall SERS enhancement effect: the electromagnetic (EM) and chemical (CHEM)
enhancement mechanisms. Electromagnetic enhancement is due to the increased
local electric field incident on an adsorbed molecule at a metallic surface, due to
visible light absorption by the metal. Chemical enhancement results from electronic
resonance/charge transfer between a molecule and a metal surface, which leads to
an increase in the polarizability of the molecule [3–5].
The Raman enhancement technique was first observed by Fleischmann’s group
on the surface of a silver electrode [2]. This enhancement response was due to the
interaction of the rough metal surface leading to the increase of the inelastic collision signal [2]. The presence of the metal surface roughness increased the scattering
effect and led to better sensitivity [2]. Surface-enhanced Raman spectroscopy is a
growing chemical field due the recent advances in the nanoscience and nanotechnology fields. Enhancements of 10
6 are often claimed and higher values are seen
in specific instances [4–7]. Even single molecule detection was reported by several
groups when employing nanoscale materials [8].
Nanoparticles with large surface area and unique characteristics that are distinct
from their bulk material provide an attractive possibility for exploring the enhancement of inelastic scattering signal [8]. Surface-enhanced Raman spectroscopy
(SERS) has been explored through using nanoparticles to increase the Raman signal
for sensing, bioanalysis, catalytic analysis, and environmental applications [2, 4, 8,
9] (Fig. 1).
In metal nanoparticles, namely gold and silver nanoparticles, “plasma oscillations”, which are collective oscillation of electrons, driven by external electromagnetic fields are localized and lead to strong resonances at specific wavelengths that
are dependent on the particle size, shape, and the local dielectric environment [4,
7]. Localized surface plasmon resonance (LSPR) has the greatest contribution to
surface-enhanced Raman spectroscopy (SERS) as electrons oscillate at nanoparticle
surfaces [3–8].
Gold and silver nanoparticles have been widely used for applications in surfaceenhanced Raman spectroscopy (SERS) studies because of their unique properties
[3–6]. They are highly stable, and their plasmonic properties occur in the visiblenear IR range allowing the optical properties to be easily controlled and monitored
[4, 6, 10]. In the previous research, it has been found that bimetallic silver–gold