Refractive Index Sensitivity of
Dye-Doped Silica-Coated
Gold Nanorods In Various
Organic Solvents
Kayla Love
Langston University
Dr. Katherine Willets Research Group
Department of Chemistry and Biochemistry,
University of Texas at Austin
Importance of Nanoparticles
Noble metal nanoparticles have optical
properties that can be beneficial for
• biological applications
• surface enhanced spectroscopy
• catalysis
Where do these optical properties come from?
Plasmon
Plasmon: a collective oscillation of surface conduction electrons
in materials with a negative real and small positive imaginary
dielectric constant.
• The plasmon provides the color for a nanoparticles.
• The plasmon resonance is sensitive to the local refractive index.
Key Terms
• Refractive index: also called index of refraction is a
measure of the bending of a ray of light when
passing from one medium into another.
• UV-Vis Spectrometer: measures the amount of light
that is absorbed by a molecule.
Experimental Setup
Purpose of Study
• It is known that silica
coated AuNRs have a
linear wavelength
response to increasing
refractive index.
max  n
Do we still maintain a linear response if we include dye in the
silica shell of gold nanorods rinsed in various organic
solvents?
Langmuir 25 (2009) 9441- 9446
Overview Of Purpose
Test if the presence of dye will alter the bulk
UV-Vis spectra
Maintain the linear trend between the
refractive index and the wavelength of gold
nanorods rinsed in various organic solvents
Nanoparticle Shape
• The wavelength for a nanoparticle shape becomes smaller as
the curvature of a metal nanoparticle gets shorter.
• Nanospheres appear at 530 to 550 nm and Nanorods appear
between 650 and 850 nm
850 800 750 700 650 600 550 500
(nm)
Au Nanorods
• Prepare AuNR seed solution from a mixture of sodium
borohydride, chloroauric acid, and cetyltrimethylammonium
bromide (CTAB).
• Prepare growth solution from a mixture of chloroauric acid, CTAB,
ascorbic acid, hydrochloric acid, and silver nitrate.
• Mix the growth solution with the diluted seed solution.
Transmission Electron Microscopy
(TEM) image of AuNR
UV-Vis Spectrum
Etching
• Add AuNR solution with hydrochloric acid
and heat in water bath at 55° Celsius.
• Monitor the blue shift over time.
Time
Dye-Doped Silica Coating
Synthesis Procedure
• Mix AuNR solution with tetraethyl orthosilicate
(TEOS) in methanol and NaOH to form a
porous silica shell
• Nile red dye is added to the reaction mixture
for dye doping.
• The pores allow solvent to access the AuNR
core
Nano Lett. 9, (2009)
3896- 3903.
TEM images of dye-doped silica-coated AuNRs
Refractive Index Sensitivity
UV-Vis spectra of dye-doped
silica-coated AuNRs in
different solvents.
Refractive Index Sensitivity
Significance
nanorods with a dye- doped silica
shell will give you one senor with
two ways of detecting it.
white light detects the
scattering of the nanorod
done in Localized Surface
Plasmon Resonance
Spectroscopy (LSPR)
experiments .
laser sources detect the
fluorescence of the dye in the
silica shell.
One would no longer be stuck having to chose between two excitation source because
now you can use either.
Summary
Synthesized AuNRs and etched them smaller using
hydrochloric acid.
Silica coated the AuNR and added Nile red into the
pores of the silica.
The plasmon resonance of the dye-doped silica- coated
AuNRs changes in different solvents.
A plot of the maximum longitudinal peak against the
refractive index determined that there was a linear
trend.
Conclusion
• The dye did alter the bulk UV-Vis Spectra
• Maintained the linear trend between the
refractive index and the wavelength of gold
nanorods rinsed in various organic solvents
Future Studies
Conduct test to determine whether nile red
dye is capable of leeching out of the pores of
the silica shell and into the solution.
References
• Chen, Huanjun, Lei Shao, Kat Choi Woo, Tian Ming, HaiQing Lin, and Jianfang Wang. "Shape-Dependent Refractive
Index Sensitivities of Gold Nanocrystals with the Same
Plasmon Resonance Wavelength." The Journal of Physical
Chemistry C 113 (2009) 17691-7697
• Mayer, Kathryn M., Seunghyun Lee, Hongwei Liao, Betty C.
Rostro, Amaris Fuentes, Peter T. Scully, Colleen L. Nehl, and
Jason H. Hafner. "A Label-Free Immunoassay Based Upon
Localized Surface Plasmon Resonance of Gold Nanorods."
ACS Nano 2 (2008) 687-92
• Ming, Tian, Lei Zhao, Zhi Yang, Huanjun Chen, Lingdong
Sun, Jianfang Wang, and Chunhua Yan. "Strong Polarization
Dependence of Plasmon-Enhanced Fluorescence on Single
Gold Nanorods." NanoLetters 11 (2009) 3896- 3903
Acknowledgments
Questions?