Fundamentals and Applications of Surface Enhanced Raman …
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Fig. 10 a TEM image of Cu/phen colloid. Inset is the core–shell image of a Cu particle. b SERS
spectra of Phen in Cu colloid (red) and from a dry Cu particle layer (blue) c SERS spectra of bipy
in Cu colloid (red) and with a dry Cu particle layer (blue). Adapted with permission from [26].
Copyright 2020 American Chemical Society
surface Plasmon resonance (LSPR) band in the visible region is the main reason
behind the origin of SERS spectra. Among conventional metals, Au is very costly,
while Ag and Cu get easily oxidized which reduces their detection efficiency. In order
to address this issue, researchers investigated Graphene as SERS substrate. Graphene
is a single layer of sp
2 hybridized carbon atoms having delocalized pi electrons. It
neither acts as complete metal system nor like semiconducting system but it behaves
like a semimetal. The use of graphene for SERS was performed in 2009 [11]. Ling
et. al. used the graphene for the detection of dye molecule such as phthalocyanine
(Pc), R6G, PPP, and crystal violet (CV) [39]. They prepared the Graphene substrate
over SiO 2 /Si via mechanical exfoliation using scotch tape. Figure 11a shows the
Raman spectra of R6G in water (blue line) and the Raman spectra of R6G on singlelayer graphene substrate. In case of R6G in water, a strong fluorescence (FL) was
observed and FL was reduced in case of SERS spectrum of R6G on graphene. The
observation of the R6G peak on a graphene substrate attributed to graphene-induced
FL quenching [11]. The Raman intensity of Pc molecule on monolayer graphene
was found much higher than on the non-graphene area, as shown in Fig. 11c. This
enhancement is due to the chemical mechanism and it is a short-range effect that
required the coupling of molecule with substrate.
Recently we also demonstrated the SERS applications of few layer reduced
graphite oxide (rGO) prepared via hydrothermal method [40]. In this work, reduction
of the prepared GO was performed using two different reducing agents, hydrazine
hydrate and urea to make rGO-HH and rGO-Urea. The rGO-HH and rGO-Urea were
used for R6G detection. To prepare the SERS substrate, rGO surface was modified
with R6G solutions (different concentrations 10
−3 M to 10
−6 M) and the prepared
mixture was drop casted over cleaned Si substrate. The SEM images of rGO-HH
and rGO-urea are shown in Fig. 12a, b, respectively. The SERS spectra of R6G
(1 mM to 1 μm) adsorbed on rGO-HH and rGO-Urea are shown in Fig. 12c, d. In
this experiment, we detected upto micromolar concentrations of R6G on both the
rGO samples. The main reason behind the detection of micromolar concentrations
is charge transfer between the adsorbed R6G molecule and rGO.
201
Fig. 10 a TEM image of Cu/phen colloid. Inset is the core–shell image of a Cu particle. b SERS
spectra of Phen in Cu colloid (red) and from a dry Cu particle layer (blue) c SERS spectra of bipy
in Cu colloid (red) and with a dry Cu particle layer (blue). Adapted with permission from [26].
Copyright 2020 American Chemical Society
surface Plasmon resonance (LSPR) band in the visible region is the main reason
behind the origin of SERS spectra. Among conventional metals, Au is very costly,
while Ag and Cu get easily oxidized which reduces their detection efficiency. In order
to address this issue, researchers investigated Graphene as SERS substrate. Graphene
is a single layer of sp
2 hybridized carbon atoms having delocalized pi electrons. It
neither acts as complete metal system nor like semiconducting system but it behaves
like a semimetal. The use of graphene for SERS was performed in 2009 [11]. Ling
et. al. used the graphene for the detection of dye molecule such as phthalocyanine
(Pc), R6G, PPP, and crystal violet (CV) [39]. They prepared the Graphene substrate
over SiO 2 /Si via mechanical exfoliation using scotch tape. Figure 11a shows the
Raman spectra of R6G in water (blue line) and the Raman spectra of R6G on singlelayer graphene substrate. In case of R6G in water, a strong fluorescence (FL) was
observed and FL was reduced in case of SERS spectrum of R6G on graphene. The
observation of the R6G peak on a graphene substrate attributed to graphene-induced
FL quenching [11]. The Raman intensity of Pc molecule on monolayer graphene
was found much higher than on the non-graphene area, as shown in Fig. 11c. This
enhancement is due to the chemical mechanism and it is a short-range effect that
required the coupling of molecule with substrate.
Recently we also demonstrated the SERS applications of few layer reduced
graphite oxide (rGO) prepared via hydrothermal method [40]. In this work, reduction
of the prepared GO was performed using two different reducing agents, hydrazine
hydrate and urea to make rGO-HH and rGO-Urea. The rGO-HH and rGO-Urea were
used for R6G detection. To prepare the SERS substrate, rGO surface was modified
with R6G solutions (different concentrations 10
−3 M to 10
−6 M) and the prepared
mixture was drop casted over cleaned Si substrate. The SEM images of rGO-HH
and rGO-urea are shown in Fig. 12a, b, respectively. The SERS spectra of R6G
(1 mM to 1 μm) adsorbed on rGO-HH and rGO-Urea are shown in Fig. 12c, d. In
this experiment, we detected upto micromolar concentrations of R6G on both the
rGO samples. The main reason behind the detection of micromolar concentrations
is charge transfer between the adsorbed R6G molecule and rGO.