1) The document discusses using silver nanoparticles to enhance Raman scattering signals through surface enhanced Raman spectroscopy (SERS) for studying heat transport in quantum dots. 2) Different methods for synthesizing silver nanoparticles were explored and nanoparticles were used to significantly enhance, by at least a factor of 90, the Raman signal of a test molecule (crystal violet). 3) For future work, the researchers want to use the silver nanoparticles to enhance Raman scattering from quantum dots to study heat transport in these nanomaterials.

1. Abstract
Heat transport through nanomaterials such as quantum dots (QDs) is essential for
engineering their use in applications such as LEDs and TVs. Vibrational spectroscopy
techniques such as Raman spectroscopy can be used to study heat transport in these
materials; however, the Raman scattering process is very weak, which limits the signal.
One way to solve this issue is to enhance the Raman scattering by the use silver
nanoparticles resonant at Raman laser wavelength, through a process called Surface
Enhanced Raman Spectroscopy (SERS). In this work, different methods for silver
nanoparticles synthesis were explored, and the resulting nanoparticles were used for
SERS with crystal violet as a test analyte. As a result, the Raman signal was enhanced
significantly, by at least a factor of 90. For future work, we want to extend the use of
the Ag NPs for SERS with QDs to study heat transport in these materials.
Background
Acknowledgements
We thank the MIT MSRP program for
funding this research.
Conclusion
References
Motivation
Future work
Methods and Results
Synthesis of Silver Nanoparticles with Plasmonic Resonance at 785 nm
Thibault Joseph Twahirwa1, Jolene Mork2, William A. Tisdale2
1Department of Physics & Dual-Degree Engineerings, Morehouse College
2Department of Chemical Engineering, Massachusetts Institute of Technology
Why nanoparticles?
They have unique optical properties
 Localized Surface Plasmon resonance ( LSPR)
Why silver nanoparticles?
Silver has the highest quality factor ( the surface
plasmon strength) across the spectrum from 300 to 1200
nm.
Silver also exhibits the highest thermal and electrical
conductivity of all metals.
Silver is relatively cheap
 Continue SERS optimization to achieve specific sizes and shapes
 Use Ag NPs to enhance Raman scattering from QDs
 Reproducible synthesis of silver nanoparticles with defined size.
 Synthesis of silver nanoparticles of define shapes.
 Use synthesized Silver nanoparticles to enhance Raman signals( SERS).
• Successfully synthesized Ag NPs of different sizes
• Achieved triangular (prism) shapes
• Best method for synthesis was the no light exposure method by Aherne, et al.
• Demonstrated successful surface enhancement of Raman signal
0
0.2
0.4
0.6
0.8
1
300 400 500 600 700 800
NormalizedAbsorption(AU)
Wavelength ( nm)
5 hours
72 hours
96 hours
0
0.2
0.4
0.6
0.8
1
300 400 500 600 700 800 900 1000
NormalizedAbsorption(AU)
Wavelength( nm)
24 hours
5 hours
100 hours
124 hours
148 hours
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
-800 -300 200 700
Intensity
Wavenumber
Crystal violet
Crystal violet +
AgNPs( Spheres)
Crystal violet +
AgNP_
Nanoprisms
Synthesis using Silver Nitrate (AgNO3) 1
 Reagents
• Na3C6H5O7 (0.3mM)
• AgNO3 (100ml of 0.1mM)
• NaBH4 (1ml of 50mM)
• PSSS (Polysodium
styrenesulphonate) 5mM/2ml
 Conditions:light exposure
70hours
Synthesis without light exposure 3
 Reagents
• Na3C6H5O7 5ml of 2.5mM
• AgNO3 5ml of 0.5mM
• NaBH4 0.3ml of 10mM
• PSSS 2.5mM/5ml
• Ascorbic Acid 75μl/10mM
Synthesis using Silver perchlorate (AgClO4 ) 2
 Reagents
• AgClO4 (1ml/0.01M) at 0 °C
• 99 mL of an ice cold
solution of 1 mM NaBH4
and 0.30 mM Na3C6H5O7
water.
• Conditions : light exposure
100hours
1. “Photoinduced Conversion of silver Nanopheres to Nanoprisms” Jin, et al. (Science) 2001.
2. “Optical Properties and Growth Aspects of Silver Nanoprisms Produced by a Highly Reproducible and Rapid Synthesis at Room
Temperature. ” Domian Aherne et al. (Advanced functional Materials) 2008.
3. “Spectral Control of Plasmonic Emission Enhancement from Quantum Dots near Single Silver Nanoprisms.” Keiko Munechika
et al, 98195-1700.Nano Lett., 2010, 10 (7), pp 2598–2603.
4. “Localized Surface Plasmon Resonance Spectroscopy and Sensing.” Willets and Van Duyne. (Annu. Rev. Phys. Chem) 2007.
0
0.2
0.4
0.6
0.8
1
300 400 500 600 700 800 900
NormalizedAbsorption(AU)
Wavelength (nm)
seed
650 μl
500 μl
400μl
120 μl
90 μl
20 μl
SERS (Surface-enhanced Raman spectroscopy)
A.
B.
C.
UV-Vis spectrum (A)
shows little change with
illumination time.
TEM images (C) show
only spherical
nanoparticles even after
96 hours.
Samples illuminated for 96 hrs.
with fluorescent light
T = 72 hrs
A.
B.
Seed solutions ( L) and
Illuminated solution(R) with
fluorescent light
UV-Vis spectrum (A)
demonstrates changes
with illumination time.
TEM images (C) show
triangle nanoparticles are
formed.
C.
A.
B.
C.
D. E.
Silver Nanoparticle synthesis
SERS sample preparation
Figure – A surface plasmon is characterized
as a surface charge density wave at a metal
surface. 4
UV-Vis spectrum (A) shows changes with different amount of seeds solution. Set up (B) was used to control the silver amount injected into
a seed solution. Image (C) shows color shift as the seed amount decrease. TEM images (D) and (E) show silver nanoprisms synthesized
using this method.
Crystal violet
molecule
Raman Signal was enhanced by the factor of >90
using silver nanoprism.
T = 148hrs
C.