1. Surface Enhanced Raman Scattering: Applications and methods
Brandon Scott
CHEM 4930

2. Introduction to Raman
CV Raman observes the Raman effect using a telescope pointed at the sun

3. Why Gold? – Free Electron Metals
The Group IA and IB elements have a free s electron configuration.
Both groups exhibit resonance.
Group IA is chemically “very” reactive and not practical for SERS .
Group IB are “noble metals” they are very unreactive.
SERS Metals

4. Localized Surface Plasmon Resonance Theory
Source E field
Metal Oxide
Local Field
Explanation + - + - + -
The electric field next to the metal oxide particle is less than the original field. + -
Gold Particle
The electric field next to the gold nanoparticle is greater than original field. This is a resonance induced by energy from the local field producing a larger local field. + - + - + - + - + - - +

5. Surface Enhanced Raman Scattering
I  m
molecule adsorbed onto surface particle - m a = E +
m = electric field-induced dipole moment - + +
Surface-enhanced Raman scattering (SERS) enhances the Raman signal of molecules adsorbed to a rough metal surface by several orders of magnitude, making it a valuable tool for trace analyte detection. Gold nanoparticles (NPs), ranging from nm in diameter, are easily synthesized in the laboratory and have a long shelf-life. Alone, these particles have virtually no Raman signal, but when tagged with any Raman-sensitive molecule there is an enormous molecular signal enhancement. + +
a = polarizability
E = electric field
surface particle

6. Nanoparticle Synthesis
Gold nanoparticles were synthesized using a known reaction method1. 20 mg of HAuCl4•3H2O was added to 200 mL of hot H2O with rapid stirring and the solution was brought to a rapid boil.
1.2 mL of aqueous sodium citrate solution (1% w/v) was added to the gold solution and the reaction flask was covered with a watch glass.
After 20 min, the heat was turned off and the violet reaction product was cooled to room temperature while stirring.

7. Single nano-particle
60kx 200nm
100nm
100kx 50nm

8. Nile blue signal enhancement using NaCl:
400
450
500
550
600
650
700
750
Fig 1: Raman spectra of colloids in 1.6 µM nile blue (blue); colloids in 1.6 µM nile blue and 31.3 mM NaCl (red).

9. SERS Limitations
The addition of analyte/NaCl leads to NP instability and eventual precipitation of Au.
Spectroscopic analysis with a narrow beam leads to a high limit of detection.
Laser Beam
Nanoparticles
Sample

10. Solution: Shelled Raman Reporters
A known method for coating gold nanoparticles with amorphous silica3-8 was tested using the synthesized colloids.
Thiol species form a strong bond to metal nanoparticles2 which leads to a strong SERS signal. It is unaffected by the silation reaction process, making it a suitable tag for core-shell particles.
Stable, shelled Raman reporters can be implemented into immunoassays for indirect detection of analytes using antibody-antigen interactions

11. Shelled Raman Reporter Synthesis
Used 1.2 mM BPE in isopropyl alcohol (IPA) to tag NOV colloids. [BPE] = 5 uM
Added 4 mL of tagged colloids, 500 uL ammonium OH, and 16 uL TEOS to 16 mL IPA.
After 1 h stirring, the solution was centrifuged at 7100 RPM for 10 min. The supernatant was poured off and the pellet was suspended in 1 mL H2O. This solution was centrifuged again and the pellet was suspended in 0.5 mL H2O.
Analyte-specific antibodies were adsorbed to the shell surface.

12. Dynamic Light Scattering results:
Colloids were analyzed before and after shelling. Shelled Raman reporters exhibit a larger diameter than bare NPs with little change to the polydispersity.

13. Shelled colloids maintain SERS BPE signal:
200
400
600
800
1000
1200
1400
1600
1800
Raman Spectra of unshelled NPs in 5 µM BPE(red, integration time: 2 sec) and shelled BPE-tagged NPs (green, integration time: 4 sec ).

14. Coated NPs + PhSH are stable:
200
400
600
800
1000
1200
1400
1600
Raman spectra of thiophenol-tagged coated NPs taken on 10/1 (blue), 10/8 (green), and 10/29 (red).

15. Paramagnetic Pull-Down Assays
Analyte binding coating
Raman coating
Analyte
shell
SERS Active Nanoparticle
Paramagnetic Particle B

16. Paramagnetic Assay Results:
Adjusted BPE signal intensity
Percent Rabbit Serum added to solution
Graph shows SERS marker peak intensity vs. Rabbit serum concentration. Shelled Raman reporters and paramagnetic particles were coated in polyclonal anti-rabbit antibody.

17. Assay Multiplexing A Binding Events B C
Reagent 1 - Paramagnetic Particle
Antigen 1
Reagent 2 - SERS Reporter
Multiplexing
Antigen 2
Reagent 3 - SERS Reporter
Antigen 3
Reagent 4 - SERS Reporter

18. Future works Cholera, LPS, CN, melamine detection
Solid/hollow Si-Au-tag-Si particles

19. References
Frens, G. Nature (London), Physical Science, 1973, 241 (105), 20.
2. Carron, K., Environ. Sci. Technol., 1992, 26 (10),
3. Lu, Y., Nano Letters, 2002, 2 (7),
4. Jana, N. R.; Earhart, C.; Ying, J. Y., Chem Mater 2007, 19,
5. Stober, W.; Fink, A.; Bohn, E., Journal of colloid and interface science 1968, 26,
6. Liz-Marzan, L. M.; Giersig, M.; Mulvaney, P., Langmuir 1996, 12,
7. Hall, S. R.; Davis, S. A.; Mann, S., Langmuir 2000, 16,
8.  Natan, M. J. Surface enhanced spectroscopy-active composite nanoparticles. 2003

20. Acknowedgements
Special thanks to Dr. Keith Carron, Virginia Schmit, Patrick Johnson’s laboratory for access to the Brookhaven Instruments ZetaPALS, and INBRE for project funding.