ꢀ
5
1
in Fig. 4a. While very broad signals observed between
0
M MB solution with an increased laser power of 1 mW as
ꢀ1
1400 and 1600 cm for the reaction supernatant in Fig. 4b
can be attributed to the surface adsorbed thiophene derivatives.
ꢀ5
On the other hand, GN3 treated with 10 M MB solution
ꢀ
1
clearly showed an intense signal at 1623 cm
(Fig. 4g).
Different concentrations of MB solutions were tested to
estimate the detection limit using the GN3 (Fig. 4c–f). Surprisingly,
we could observe the characteristic Raman signal of MB up to
ꢀ
9
1
0
M concentration (Fig. 4c). The enhancement factor (EF)
8
was estimated to be B2.0 ꢂ 10 (Fig. S13, ESIw). The SERS
intensity is quite reliable. We undertook another SERS experi-
ment using crystal violet (CV) with varying concentrations
Fig. 4 Concentration-dependent Raman spectra of (a) the MB
ꢀ
1
ꢀ5
(Fig. S14, ESIw). The characteristic CV signal at 1617 cm
8
solution (1 ꢂ 10 M) on a flat Au coated glass, (b) the supernatant
ꢀ
of the reaction mixture without MB treatment, and MB solutions on
ꢀ8
was also successfully detected up to 10 M concentration.
However, we did not observe any signal enhancement with an
excitation at 514 nm (Fig. S15, ESIw).
ꢀ9
GN3 samples on a Si wafer (c) 1 ꢂ 10 M, (d) 1 ꢂ 10 M,
ꢀ
7
ꢀ6
ꢀ5
(
e) 1 ꢂ 10 M, (f) 1 ꢂ 10 M, and (g) 1 ꢂ 10 M. The chemical
structure of MB is drawn together.
In summary, the use of 2-thiophenemethanol as a reducing
agent for the preparation of nanoscale Au materials is an
efficient method to obtain anisotropically grown Au nano-
sheets with an unprecedented structural motif and superb SERS
activity. The high EF can be attributed to the well-developed
nanogap hotspots which are evenly distributed in the Au
nanoleaves. We envision that the nanogap-rich Au nanoleaves
would be applicable to many useful applications.
which selectively block the certain lateral growth directions of Au
nanoleaves.
The formation of various 2-thiophenemethanol derivatives
was confirmed from ESI mass spectrometry analysis of the
reaction mixture (Fig. S9, ESIw). There are various species
derived from 2-thiophenemethanol as well as a simple
oxidized product, 2-thiophenecarboxaldehyde. Therefore, the
oxidation might occur through both the oxidative coupling of
This work was supported by the Gyeonggi Regional
Research Center (GRRC) program of Gyeonggi province
2-thiophenemethanol and oxidation of the hydroxymethyl
group of 2-thiophenemethanol.
(
GRRC-HUFS-2010-A01).
X-Ray photoelectron spectroscopy (XPS) revealed the state
of Au atoms in GN samples. Au 4f peaks found at 87.32 eV
Notes and references
(
4f5/2) and 83.57 eV (4f7/2) confirmed the zero-valent metallic
1
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1
2
Au state (Fig. S10, ESIw). In addition, there are S 2s, S 2p, C
s, and O 1s peaks and this indicates that the oligomerized
1
2
3
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on the surface of Au nanoleaves because of the strong
tendency of a S atom to the Au surface (Fig. S11, ESIw). They
may play a key role in inducing the flat geometry with a (111)
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of the (111) plane. We speculate that the sulfur-contaning
organic species are also responsible for the nanogap formation.
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methanol under the same reaction conditions, a quite different
product was obtained. The latter can polymerize to form high
molecular weight polythiophenes due to the free 2- and
4
5
6
7
(a) R. Jin, Y. C. Cao, E. Hao, G. S. Metraux, G. C. Schatz and
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5
-positions. The TEM image of the product showed small
monodispersed Au nanoparticles completely surrounded by
the polythiophene conducting polymer matrix (Fig. S12, ESIw).
The presence of a nanometre range of gaps will induce an
enhanced localized electric field for an efficient Raman signal
enhancement for analytes located in the gaps. To verify the
Raman signal enhancements, GN3 was spin-coated on a Si
wafer and varying concentrations of aqueous methylene blue
8
9
(a) T. Soejima and N. Kimizuka, Chem. Lett., 2005, 1234;
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1
(
characteristic Raman signal at 1623 cm
MB) solutions were treated on the substrate. MB has a
ꢀ
1
1 (a) H. Li, J. Jo, J. Wang, L. Zhang and I. Kim, Cryst. Growth Des.,
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1 13
.
The peak intensity
was compared with that of pure MB on a control flat Au
1
2 K. Y. Lee, M. Kim, J. Hahn, J. S. Suh, I. Lee, K. Kim and
S. W. Han, Langmuir, 2006, 22, 1817.
coated microscope slide glass purchased from Aldrich (layer
˚
thickness 100 A, catalog no. 643203). As expected, no
signals were detected for the highest concentration sample of
1
3 D. A. Walker, K. P. Browne, B. Kowalczyk and B. A. Grzybowski,
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This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 6963–6965 6965