Transcript Document

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
SEFS Applications
Metals
Aluminum
Silver
Gold
Copper
Nanoholes
Nanoparticles
Thin Films
– High index materials and specific
optical geometry --> 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 2
J. R. Lackowicz et. al. Proc. Of SPIE, 6099, 609909-1 (2006)
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
y
x
AR= x
y
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 d=150 nm hole
(b) 3-D finite-element time-domain simulation of
intensity distribution for a d=50 nm nanohole
•
•
Lifetime reduction from 3.87 ns in
open solution to 0.9 ns above
nanohole
Effects of nanohole diameters and
periodicity
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J. Phys. D: Appl. Phys. (2008) 41, 013001
Theory: SEF in Ag Nanoshells
• Quantum Dots are highly
photostable.
• Light absorbed by metal -->
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 --> 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
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J. Phys. D: Appl. Phys. (2008) 41, 013001
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