Slide 1

Surface-Enhanced Raman Scattering (SERS) Laser Excitation ( 0 ) Raman Scattering ( 0 vib ) = E ChemicalElectromagnetic Haynes, McFarland, and Van Duyne, Anal. Chem.,77, 338A-346A (2005). Enhancement Factor (EF) = SERS Raman

Slide 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 ) No roughness requirement Contributes EF ~ 10 2 10 4 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 > 10 4

Slide 3

Localized Surface Plasmon Resonance Non-resonantResonant 1) 1)Resonant is absorbed 2) 2)EM fields localized at nanoparticle surface

Slide 4

Metal Salt Reducing Agent Capping Agent Metal Colloids coated with Reducing Agent/Capping Agent heat or sonication h Aged Metal Colloids Noble Metal Nanoparticles

Slide 5

50 nm D = 24.8 4.1 nm Noble Metal Nanoparticles

Slide 6

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

Slide 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.

Slide 8

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. 20 m

Slide 9

Measuring the LSPR Wavelength (nm) S c a t t e r i n g I n t e n s i t y 400500600700800900 0 200 400 600 800 1000 400500600700800900 0 200 400 600 800 1000 S c a t t e r i n g I n t e n s i t y 400500600700800900 0 200 400 600 800 1000 S c a t t e r i n g I n t e n s i t y 400500600700800900 0 200 400 600 800 1000 S c a t t e r i n g I n t e n s i t y

Slide 10

LSPR Dielectric Response Blue = N 2 (1.000), Green = Methanol (1.329), Red = 1-Propanol (1.385), Purple = Chloroform (1.446), Orange = Benzene (1.501)

Slide 11

Single Nanoparticle Sensing Proof of Concept Wide-field Image

Slide 12

Biosensing with Single Nanoparticles Streptavidin: 60kDa Tetrameric Protein ~4 nm x 4 nm x 5nm Biotin: Vitamin H K a = 10 14 M -1 http://relic.bio.anl.gov

Slide 13

Biosensing with Single Nanoparticles 450500550600 0 400 800 1200 508.0520.7 Wavelength (nm) I n t e n s i t y max = +12.7 nm Conc = 10 nM SA ~700 SA molecules max = +12.7 nm Conc = 10 nM SA ~700 SA molecules Monitoring Biotin-Streptavidin Binding with Single Nanoparticles

Slide 14

Comparison of Unenhanced and Enhanced Raman Spectra

Slide 15

Relationship between the LSPR and Laser Wavelength max = 690 nm 1575 cm -1 band N = 13 points Range = 475 700 nm High = 662 nm EF = 1.9 x 10 7 max = 690 nm 1575 cm -1 band N = 13 points Range = 475 700 nm High = 662 nm EF = 1.9 x 10 7

Slide 16

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

Slide 17

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

Slide 18

Are you getting the concept? Why hasnt surface-enhanced Raman replaced normal Raman completely? In other words, why would someone do a normal Raman scattering experiment?

Slide 19

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

Slide 20

Polychlorinated Biphenyls (PCBs) Present in soil, water, and air worldwide Classified as persistent organic pollutants Analysis traditionally done by GC-MS Complicated by low concentrations and multiple congeners Prohibitively difficult for in situ environmental analysis

Slide 21

Partitioning PCBs

Slide 22

Other Experiments Use band intensities and shifts to understand the partitioning mechanism Environmental interferants not a problem Substrates can be reused

Slide 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 10 14 molecules/cm 2 ), and measures the spectrum with a laser spot size of 1.26 mm 2. The intensity of the 1000 cm -1 shift ring breathing stretch is 35793 adus. For her standard, she puts undiluted benzenethiol ( = 1.073 g/cm 3 ) 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)?

Slide 24

Single Molecule SERS S. Nie, et. al. Science 1997, 275, 1102-1106 EF= 10 14 -10 15 ! K. Kneipp, et. al. Phys. Rev. Lett. 1997, 78, 1667-1670

Slide 25

Hyper Raman and Surface-Enhanced Hyper Raman Spectroscopy With focused, pulsed laser, you can induce a non- linear interaction: Incident: 0 Scattered: 2 0, 2 0 1 Selection Rules: All IR active modes are also hyper-Raman active Some hyper-Raman active modes are neither IR or Raman active

Slide 26

Coherent Anti-Stokes Raman Phase-match p and s in a four wave mixing process: Incident: p, s Scattered: 2 p - s CARS Advantage: The AS signal beam is spatially and temporally removed from the fluorescence signal. I CARS ~ I p 2 I s Large signal when: p - s = p - s =