Surface Enhanced Fluorescence

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Surface Enhanced Fluorescence

• Ellane J. Park
• Turro Group Meeting
• July 15, 2008

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Surface Enhanced Fluorescence (SEF)

• Motivation biological systems
• Enhancement of Fluorescence Intensity
• Adjust fluorescence lifetime
• Techniques to couple SPP and photons
• High index materials and specific optical
  geometry --gt Increase momentum of photon
• Example metal on glass (e.g. Kretschmann
  configuation)
• Break up translational motion with corrugated or
  roughened metallic surfaces.

J. Phys. D Appl. Phys. (2008) 41, 013001
J. R. Lackowicz et. al. Proc. Of SPIE, 6099,
609909-1 (2006)
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SEF Distance and Orientation Dependence

• What is the enhancement factor?
• Magnitude of increase in fluorescence intensity
  of fluorophore in presence of metal, compared to
  that of fluorophore in the absence of metal
• Distance
• Less than 10 nm Non-radiative energy transfer
  can occur (i.e. quenching)
• Greater than 10 nm Fluorescence Intensity can be
  enhanced by up to 100-fold
• Dipole Orientation
• Dipoles that oscillate perpendicular to surface
  couple efficiently with surface plasmon modes

Calculated Fluorescence intensity of free
fluorophore as a function of distance to Au NP
J. Phys. D Appl. Phys. (2008) 41, 013001
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Fluorescence Intensity of Au Nanorods
CSR. 35, 209 (2006)
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Fluorescence Enhancement in Nanoholes
(a) Fluorescence decay curves of Rhodamine 6G in
open solution and into a d150 nm hole
(b) 3-D finite-element time-domain simulation of
intensity distribution for a d50 nm nanohole

• Lifetime reduction from 3.87 ns in open solution
  to 0.9 ns above nanohole
• Effects of nanohole diameters and periodicity

J. Phys. D Appl. Phys. (2008) 41, 013001
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Theory SEF in Ag Nanoshells

• Quantum Dots are highly photostable.
• Light absorbed by metal --gt fluorophore
• Potential Effects of fluorophore in Nanoshell
• Photostability (Protection from oxygen)
• Higher radiative decay rates and higher quantum
  yields
• Emission is 2-fold narrower
• Shorter lifetime --gt less time for photochemistry
  in excited state

J. R. Lackowicz et. al. Proc. Of SPIE, 6099,
609909-1 (2006)
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Thank You
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Surface Plasmons
lower e- density - higher e- density
? angular frequency c Speed of light ?
Incident angle with the normal to surface in
dielectric medium kspp In-plane wavevector of
SPP modes Kspp (greater momentum) is greater than
k0 (free space photon of same pulsation)

• Note Energy flow from fluorophore to SPP modes
  can be detrimental to SEF process

J. Phys. D Appl. Phys. (2008) 41, 013001
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