1 Surface Enhanced Fluorescence Ellane J. Park Turro Group Meeting July 15, 2008

2 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 --> Increase momentum of photon Example: metal on glass (e.g. Kretschmann configuation) –Break up translational motion with corrugated or roughened metallic surfaces. J. R. Lackowicz et. al. Proc. Of SPIE, 6099, (2006) J. Phys. D: Appl. Phys. (2008) 41,

3 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 J. Phys. D: Appl. Phys. (2008) 41, Calculated Fluorescence intensity of free fluorophore as a function of distance to Au NP

4 Fluorescence Intensity of Au Nanorods CSR. 35, 209 (2006) y x AR= x y

5 Fluorescence Enhancement in Nanoholes 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, (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

6 Theory: SEF in Ag Nanoshells J. R. Lackowicz et. al. Proc. Of SPIE, 6099, (2006) 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

7 Thank You

8 Surface Plasmons J. Phys. D: Appl. Phys. (2008) 41,  : angular frequency c: Speed of light  : Incident angle with the normal to surface in dielectric medium k spp : In-plane wavevector of SPP modes K spp (greater momentum) is greater than k 0 (free space photon of same pulsation) +: lower e- density -: higher e- density Note: Energy flow from fluorophore to SPP modes can be detrimental to SEF process

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