Surface-Enhanced Raman Scattering (SERS)

1. m = aE sSERS sRaman Enhancement Factor (EF) = Chemical Electromagnetic Surface-Enhanced Raman Scattering (SERS) Raman Scattering (w0 –wvib) Laser Excitation (w0) Haynes, McFarland, and Van Duyne, Anal. Chem.,77, 338A-346A (2005).

2. SERS Enhancement Mechanisms • Chemical Mechanism: • Laser excites (a) new electronic states arising from • chemisorption or (b) shifted or broadened adsorbate • electronic states yielding a resonance condition. • Short range (1-5 Å) • No roughness requirement • Contributes EF ~ 102 – 104 • Electromagnetic Mechanism: • LSPR induces large electromagnetic fields at roughened • metal surface where molecules are adsorbed. • Long range (2-4 nm) • Affected by all factors determining LSPR • Contributes EF > 104

3. Localized Surface Plasmon Resonance Non-resonant Resonant • Resonant l is absorbed • EM fields localized at nanoparticle surface

4. Noble Metal Nanoparticles hn heat or sonication Metal Salt Reducing Agent Capping Agent Metal Colloids coated with Reducing Agent/Capping Agent Aged Metal Colloids

5. Noble Metal Nanoparticles D = 24.8 ± 4.1 nm 50 nm

6. Nanostructured Substrates http://pubs.acs.org/cgi-bin/article.cgi/ancham-a/0000/77/i17/pdf/905feature_vanduyne.pdf

7. Localized Surface Plasmon Resonance The resonance results in (1) wavelength-selective extinction and (2) enhanced EM fields at the surface. Spectral location of the LSPR is dependent upon particle size, shape, composition, and dielectric environment.

8. Field Enhancement by Metallic Spheres #1 When a metallic sphere is subject to an external electric field, E0, the field outside the sphere is given by the following equation: where the polarizability of the sphere is where a is the sphere radius and The condition for achieving the greatest external field strength occurs when the denominator in the above equation is large.

9. Beyond Metallic Spheres For spheroidal particles, the expression for g becomes: where is a variable that is calculated based on the aspect ratio of the particle. The table below lists for a few different aspect ratios. Aspect Ratio

10. Spectroscopic Consequences of Field Enhancement The SERS enhancement is determined byg in the following manner: The magnitude of the extinction and scattering cross sections are also related to g:

11. 20 mm Resonant Rayleigh Scattering Light that is elastically scattered due to the LSPR can be used as an in situ monitor of nanoparticle optical properties. The primary benefit of scattering spectroscopy is that the single-to-noise ratio is much higher than extinction spectroscopy when examining single nanoparticles.

12. 100 640 A B 588.0 600.8 510.2 574.2 611.9 80 l = 203.1*RI + 306.5 600 max y ) t 60 m i s n n ( 560 e t x a n l m I 40 520 20 480 0 450 500 550 600 650 700 1 1.2 1.4 1.6 Refractive Index Wavelength (nm) LSPR Dielectric Response Blue = N2 (1.000), Green = Methanol (1.329), Red = 1-Propanol (1.385), Purple = Chloroform (1.446), Orange = Benzene (1.501)

13. Single Nanoparticle Sensing – Proof of Concept Wide-field Image

14. Biosensing with Single Nanoparticles http://relic.bio.anl.gov Biotin: Vitamin H Ka = 1014 M-1 Streptavidin: 60kDa Tetrameric Protein ~4 nm x 4 nm x 5nm

15. 508.0 520.7 Biosensing with Single Nanoparticles Monitoring Biotin-Streptavidin Binding with Single Nanoparticles 1200 800 y t i s n Dlmax = +12.7 nm Conc = 10 nM SA ~700 SA molecules e t n I 400 0 450 500 550 600 Wavelength (nm)

16. Comparison of Unenhanced and Enhanced Raman Spectra

17. Relationship between the LSPR and Laser Wavelength lmax = 690 nm 1575 cm-1 band N = 13 points Range = 475 – 700 nm High = 662 nm EF = 1.9 x 107

18. Locating Landmines with SERS Roughened Au lex = 785 nm Sylvia, J. M. et al. Anal. Chem. 2000, 72,5834.

19. Locating Landmines with SERS 115 mW 30 sec TNT DNT DNB Sylvia, J. M. et al. Anal. Chem. 2000, 72,5834.

20. Are you getting the concept? Why hasn’t surface-enhanced Raman replaced normal Raman completely? In other words, why would someone do a normal Raman scattering experiment?

21. Partition Layers to Detect Non-Traditional Analytes with SERS – Kyle Bantz

22. Partitioning PCBs

23. Are you getting the concept? Kyle fabricates a new Ag SERS substrate and wants to calculate the EF. She doses the substrate with benzenethiol (packing density = 6.8 x 1014 molecules/cm2), and measures the spectrum with a laser spot size of 1.26 mm2. The intensity of the 1000 cm-1 shift ring breathing stretch is 35793 adus. For her standard, she puts undiluted benzenethiol (r = 1.073 g/cm3) into a cuvette with a known probe volume of 0.00413 mL and measures a 1000 cm-1 shift band intensity of 36364 adus. What is the EF (assuming that the laser power and collection time were the same for both measurements)?

24. Single Molecule SERS EF= 1014-1015 ! S. Nie, et. al. Science 1997, 275, 1102-1106 K. Kneipp, et. al. Phys. Rev. Lett. 1997, 78, 1667-1670

25. Hyper Raman and Surface-Enhanced Hyper Raman Spectroscopy With focused, pulsed laser, you can induce a non- linear interaction: Incident: n0 Scattered: 2n0, 2n0±n1 Selection Rules: All IR active modes are also hyper-Raman active Some hyper-Raman active modes are neither IR or Raman active

26. Coherent Anti-Stokes Raman Phase-match wp and ws in a four wave mixing process: Incident: np, ns Scattered: 2np - ns ICARS ~ Ip2Is Large signal when: np-ns = D D CARS Advantage: The nAS signal beam is spatially and temporally removed from the fluorescence signal.