1. 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

2. Importance of Nanoparticles
Noble metal nanoparticles have optical properties that can be beneficial for
biological applications
surface enhanced spectroscopy
catalysis
Where do optical properties come from?
Where do these optical properties come from?

3. Plasmon
Plasmon: a collective oscillation of surface conduction electrons in materials with a negative real and small positive imaginary dielectric constant.
When a metal absorbs light of a resonant wavelength it causes the electron cloud to vibrate, dissipating the energy . What this means in real terms is that there are certain wavelengths for metal where photons are not reflected, but instead are absorbed and converted into surface plasmon resonance (electron cloud vibrations).
The plasmon provides the color for a nanoparticles.
The plasmon resonance is sensitive to the local refractive index.

4. 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.

5. Experimental Setup

6. Purpose of Study
It is known that silica coated AuNRs have a linear wavelength response to increasing refractive index.
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)

7. 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

8. 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
Selective Shortening of Single-Crystalline Gold Nanorods by Mild Oxidation
Chia-Kuang Tsung,†‡ Xiaoshan Kou,‡ Qihui Shi,† Jinping Zhang,§ Man Hau Yeung,‡ Jianfang Wang,*‡ and Galen D. Stucky*†§;
Department of Chemistry and Biochemistry and Materials Department, University of California, Santa Barbara, California 93106, and Department of Physics, the Chinese University of Hong Kong, Shatin, Hong Kong, P. R. China
(nm)

9. 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

10. Etching
Add AuNR solution with hydrochloric acid and heat in water bath at 55° Celsius.
Monitor the blue shift over time.
Time

11. 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)
TEM images of dye-doped silica-coated AuNRs

12. Refractive Index Sensitivity
UV-Vis spectra of dye-doped silica-coated AuNRs in different solvents.

13. Refractive Index Sensitivity

14. laser sources detect the fluorescence of the dye in the silica shell.
Significance
nanorods with a dye- doped silica shell will give you one senor with two ways of detecting it.
laser sources detect the fluorescence of the dye in the silica shell.
white light detects the scattering of the nanorod done in Localized Surface Plasmon Resonance Spectroscopy (LSPR) experiments .
One would no longer be stuck having to chose between two excitation source because now you can use either.

15. 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.

16. 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

17. 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.

18. References
Chen, Huanjun, Lei Shao, Kat Choi Woo, Tian Ming, Hai-Qing 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)
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)
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)

19. Acknowledgments

20. Questions?