Supplementary Information for “Single molecule detection from a
large-scale SERS-active Au79Ag21 substrate”
Hongwen Liu,1,† Ling Zhang,1,† Xingyou Lang,1 Yoshinori Yamaguchi,2,3 Hiroshi
Iwasaki,2,3 Yasushi Inouye,2 Qikun Xue,1,4,* and Mingwei Chen1, 5,*
1
WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2
Department of Applied Physics, Graduate School of Engineering, Osaka University, Osaka 565-0871, Japan
3
PARC, Graduate School of Engineering, Osaka University, Osaka 565-0871, Japan
4
Department of Physics, Tsinghua University, Beijing 100084, China
5
School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030, China
†
These authors contributed equally to this work.
*
Correspondence and requests for materials should be addressed to Q.K.X. or M.W.C.
(qkxue@mail.tsinghua.edu.ac; or mwchen@wpi-aimr.tohoku.ac.jp)
1
Supplementary Methods
Nanoporous films were prepared by dealloying. The chemical composition of the nanoporous films
was controlled by the dealloying time. In this study, the optimal dealloying time of 20 seconds was
adopted to give rise to a small pore size of ~15 nm and high residual silver of ~21 at. %. The
as-prepared wrinkled substrate was put in aqueous solution of the probe molecules for 4 hours, until
the substrate surrounding environment is stabilized and the probe molecules uniformly diffused and
adsorbed on the wrinkled nanoporous film surface. The sample, which was covered by a film (about
0.2 mm thick) of aqueous solution of molecules1, was dried in air for 1 hour to immobilize the probe
molecules on the substrate surface. Molecular distribution uniformity was proved by repeatable
Raman mappings in several different regions. Taking the surface fluctuation of wrinkled films (~2.5
μm in depth) into account, we estimate the average surface density of the probe molecules to be
~0.25 per μm2 of the geometric area of the surface for 1×10-12 M solutions. RAMAN-11 features a
single-transverse-mode laser to realize spatial resolution better than 500 nm. Ultrafast and stable
Raman imaging in line optical scanning mode enables catching hot spots in probed regions, which
are otherwise highly sensitive and easily missed.
1.
Kudelski, A. Raman studies of rhodamine 6G and crystal violet sub-monolayers on
electrochemically roughened silver substrates: Do dye molecules adsorb preferentially on highly
SERS-active sites? Chem. Phys. Lett. 414, 271-275 (2005).
2
Table S1: Comparison and assignment of the Raman bands of R6G in normal Raman and SERS
spectra.
a
Watanabe, H., Hayazawa, N., Inouye, Y. & Kawata, S. DFT vibrational calculations of Rhodamine
6G adsorbed on silver: analysis of tip-enhanced Raman spectroscopy. J. Phys. Chem. B 109,
5012-5020 (2005).
b
X refers to the motion of the xanthene ring. A refers to the motion of the NHC2H5 groups. M refers
to that of a pair of methyl group adjacent to the xanthene ring. P refers to that of the phenyl ring with
the COOC2H5 group.
3
Table S2: Comparison and assignment of the Raman bands of DNA adenine in normal Raman and
SERS spectra.
a
Giese, B & McNaughton, D. Surface-enhanced Raman spectroscopic and density functional theory
study of adenine adsorption to silver surfaces. J. Phys. Chem. B 106, 101-112 (2002).
b
Def, deforming; rock, rocking; bend, bending; str, stretching; sciss, scissoring; R5, five-membered
ring; R6, six-membered ring.
4
Figure S1. SERS spectra of R6G on wrinkled nanoporous films with compositions of Au79Ag21 and
Au98Ag2 (at. %). The enhancement factor is calculated by comparing the peak intensity of single
molecules from the surface-enhanced Raman scattering (SERS) signal with that from the Raman
scattering (RS) signal1. The average enhancement factor of the wrinkled nanoporous Au98Ag2 film2
has been calculated to be ~0.7×108. The relative intensity of the nanoporous Au79Ag21 substrate is 4
times stronger than that of the nanoporous Au98Ag2 film. We thus estimate the average enhancement
factor of the wrinkled nanoporous Au79Ag21 film in this paper to be ~3×108.
1.
Le Ru, E. C., Blackie, E., Meyer, M. & Etchegoin, P. G. Surface enhanced Raman scattering
enhancement factors; A comprehensive study. J. Phys. Chem. C 111, 13794-13803 (2007).
2.
Reference 26.
5