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.

n max

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

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

One would no longer be stuck having to chose between two excitation source because now you can use either.

Summary

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, 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) 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?