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1. New Nano Architecture for SERS
Applications
Gayatri Kumari and Chandrabhas Narayana*
Chemistry and Physics of Materials Unit,
Jawaharlal Nehru Centre for Advanced Scientific Research,
Jakkur P. O., Bangalore 560064, India
J. Phys. Chem. Lett. 2012, 3, 1130-1135 1

2. Schematic to show path of light through Ag@SiO2@Au
sandwich nanoparticles resulting in multiple
reflections.
Incident light can be reflected or transmitted.
Transmitted light can undergo total internal
reflection before coming emerging out where
it again meets incident light and can interfere
constructively resulting in high field intensity
at its surface.
Scheme of formation of sandwich nanoparticles
Ag np
Ag@SiO2 Ag@SiO2@Au
Ag@SiO2@Au
seed
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3. (a) Normalized extinction spectra of silver (purple) and silver core silica shell (green) nanoparticles,
(b) Silver silica gold seed (blue), the sandwich nanoparticles (red) and silica core gold island nanoparticles (dark gray).
Figure 3: TEM images for different steps of synthesis of silver silica gold sandwich nanstructures. (a) Silver nanoparticles,
(b) silver core silica shell, (c) gold seeds on silver core silica shell nanoparticles, (d) silver silica gold sandwich nanoparticles.
The arrow in Figure (c) points to core where complete oxidation of silver has occurred. Scale bar 100 nm (a,d) and 50 nm (b,c).
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4. BET curve for Ag@SiO2 nanoparticles
FESEM of Ag@SiO2@Au sandwich nanoparticles
XRD pattern of Ag@SiO2@Au nanoparticles
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5. SERS spectra of thiophenol with Ag@SiO2@Au sandwich
nanoparticles and SiO2@Au core shell particles
SERS spectra of thiophenol on Ag@SiO2@Au sandwich nanoparticles. (b) SERS spectra of 10-5 M
thiophenol (c) SERS spectra of 10-7 M thiophenol. Laser wavelength used was 632.8 nm and power
was 8 mW at the sample.
Enhancement factor = 106
EFAg@SiO2@Au = 6X EFSiO2@Au
Detection limit of Ag@SiO2@Au is 100 times more than SiO2@Au nanoparticles
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6. Ag@SiO2 nanoparticles with different silica shell thickness
TEM images of Ag@SiO2 with 40 nm (a), 50 nm (b), 60 nm (c) silica shell. Scale bar 50 nm (a,b) and 100 nm (c).
Extinction spectra of silver core silica shell nanoparticles with different silica shell thickness (60 nm, 50 nm, 40 nm, 25 nm).
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7. Ag@SiO2@Au particles with varying silica shell thickness
TEM image showing Ag@SiO2@Au with different silica shell thickness. (a) 25 nm, (b) 40 nm, (c) 60 nm.
Scale bar 20 nm (a, b) and 50 nm (c).
Ag@SiO2@Au particles with different densities of gold island
TEM image of sandwich particles with different densities of gold island
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8. SERS spectra of thiophenol with different types of
sandwich nanoparticles
SERS spectra of thiophenol. 10-4 M concentration was used SERS spectra of 10-3 M thiophenol on SN1, SN2 and
for 40 nm and 60 nm silica shell and 1mM was used for 25 nm SN3 sandwich nanoparticles. Gold coverage on silica
silica shell sandwich nanoparticles. shell is SN1 < SN2 < SN3.
SERS EF decreased when the dielectric shell thickness was changed
OR
Gold island densities were increased or decreased
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9. Conclusions
•We have demonstrated a facile method to
synthesize Ag@SiO2@Au sandwich
nanoparticles.
•SERS EF of Ag@SiO2@Au was found to be
106 which was 6 times higher than SiO2@Au
nanoparticles under similar experimental
conditions. Gayatri Kumari
•SERS EF was found to decrease when silica
layer thickness was varied from 40 nm or
density of gold islands were changed beyond
an optimum value.
Acknowledgments
The authors acknowledge Swedish Research Links and
JNCASR for providing the financial support. We are
thankful to Dr. Usha Tumkurkar for doing the TEM Chandrabhas Narayana
measurements and Dr. Karthik Bala for the FESEM
measurements.
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