plasmon assisted nanotrapping e. p. furlani, a. baev and p. n. prasad the institute for lasers,...
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Plasmon Assisted Nanotrapping
E. P. Furlani, A. Baev and P. N. Prasad
The Institute for Lasers, Photonics and Biophotonics University at Buffalo, SUNY
Overview
Introduction
Applications
Experimental Results
Modeling Nanotrapping Systems
Summary
Optical Trapping – Laser Tweezers
D. G. Grier Nature 424 2003
Powerful tool for remote manipulation of microscopic biomaterial.
Strongly focused laser beam creates
gradient optical force that traps particles.
Not ideal for nanoscale trapping (diffraction limitation, heating).
Not well suited for integration with Lab-
on-Chip systems (opto- fluidics).
Plasmonic-based Optical Nano-trapping
Locally enhanced field near illuminated metallic nanostructures creates gradient
optical force that traps nanoparticles.
Well suited for trapping sub-wavelength metallic or dielectric particles.
Potential for integration with Lab-on-Chip
systems (opto-fluidics).
Gold Nanocones
DielectricNanoparticle
Einc(t)
p
+ -
+ - + -
+ -
Surface Plasmon Resonance (SPR)and Localized SPR (LSPR) in Metallic Nanostructures
Plasmon: Quantized charge density wave in free electron gas.
LSPR: Resonant scattering modes in
sub-wavelength metallic nanoparticles
SPR: Surface plasmons confined to metal/dielectric interface.
1/2
sin( )m dsp d
m d
k kc
Wave vectors
E(t)
- - -
+ + + - - -
+ + +
- - - + + + - - - + + + - - -
m
d
E
H.
Strong Local Field
Motivation for LSPR Nanotrapping
Higher Resolution: optical nano-manipulation of sub-
wavelength particles (d << ) (overcome diffraction limit).
Reduced Power: optical intensity an order of magnitude
lower then conventional optical tweezers
Multiplexed Nano-trapping: multiplexed parallel
manipulation of particles using arrays of metallic nanopaticles
Microsystem Integration: integrated optical particle
manipulation/separation for BioMEMS, Lab-on-a-Chip systems.
E(t)
Local Field Enhancement
Metallic Nanoparticles
Optical Absorption - Scattering
Local Field Enhancement Re ( ) 2 ( )mp d
Absorption frequency/bandwidth depend on particle size, shape, composition and surrounding media etc.
P(t) = E(t)- - -
+ + + - - -
+ + +
30
( )4
( ) 2mp d
d pmp d
R
mp
d
Analytical Dielectric Function for Au Nanostructures Experimental and analytical
dielectric values vs.
Analytical Dielectric Function for Au used in Analysis*
2
2
1,2
1
1 1
1 1 1 1 1 1
n n
Au
pp
i in
n n
n n n n
i
A e e
i i
*P. G. Etchegoin et al. J. Chem. Phys. 125, 164705 (2006)
Einc
+ -
+ - + -
+ -
Optical Trapping of Sub-Wavelength Neutral Particles
Dielectric Nanoparticle
Metallic Nanostructures
Force on Dielectric Nanoparticle caused by Local Field Gradient produced by Illuminated Metallic Nanoparticles
J. Aizpurua et al., PRL 90 2003T. Atay et al., Nano Letters 4 2004
Nano-cone Array
Nano-Pillar Array
Nano-Ring Array
Fabricated Metallic Nanostructures
Experimental Results
Optical trapping of nanoparticles using tapered metallic nanopillars
Collaboration with A. N. Grigorenko et. al, Nanometric optical tweezers based on nanostructured substrates, U. Manchester UK
1 m
120 nm
90 nm
Optical Trapping of Microbubbleson Nanostructured Substrate
A.R. Sidorov et al. Optics Communications 278 (2007)
120 nm
90 nm
Enhanced Optical Trapping Au Nanoparticle Array
Array of Au Nanostructures
Trapped Dielectric SphereMoving Dielectric Sphere
X. Maio and L. Y. Lin, Opt. Letters. 32 2007, also unpublished work 2008
Size of Trapped Particle D = 6.8 m D = 1 m D = 0.8 m
Optical Trapping Intensity (W/m2) with Au NP Array 0.71 3.4 3.8
Optical Trapping Intensity (W/m2) with Glass Slide 7.1 6.0 7.6
Plasmonic Trapping of Cells
Single Yeast Cell Trapped in Square (other cells moving at constant speed)
Trapped Cell Moving Cells
X. Maio and L. Y. Lin, IEEE J. Sel. Topics Quant. Elec. 13 2007
Optical intensity required for stable trapping of single yeast cell is 78.8 W/m2
Array of Au Nanostructures
Modeling Optical Nanotrapping
Dielectric Model for Metallic Nanoparticles.
Predict EM Field (Full-Wave Time-Harmonic Analysis)
Compute Time-averaged Optical Force Fopt on Dielectric Nanoparticles (Dipolar Force)
Identify Regions of Trapping
Use Fopt to Predict Particle Motion.
Optical Force on a Dielectric Nanoparticle
( )pillarsP E
*, 0 0
1Re ( )
2i
opt i p j jj
F E E
0 inc scatE E E
0 0
23
0
4
21
3
dp
p
kik
R
30 2
p dp
p d
R
Time-averaged Optical Dipolar Force Fopt is a function of
several variables: , p, mp (), d, and the geometry,
composition and coupling of metallic nanostructures.
d
Einc(t)
p
+ -
+ - + -
+ -mp()mp()
p
Trapping and Scattering Force Components
Re[ ] Im[ ]p p pi
3grad pF R
*, 0 0
1Re
2i
opt i p j jj
F E E
2
0
1Re[ ]
4grad pF E
6scat pF R
2
0
1Im[ ]
2scat pF E k
3pR
6pR
Trapping Potential Vtrap: Vgrad trapF
(Electric Field Energy Density)V trap eW
2 m
k
Symmetry Boundary Conditions: PEC, PMC
Full-Wave Time-Harmonic Analysis(Array of Nanopillars: Glass Substrate covered with H2O)
Computational Domain
3.4 m
2 m 2 m
PML
PML
y x
k
PEC
PMCGlass
H2O p
Symmetry Boundary Conditions: PEC, PMC
Computational Model
Computational Domain
Surface current Jx BC chosen to produce plane wave: Ex = 2106 V/m. FEA Model: 43,904 cubic vector elements with 838,485 degrees of freedom.
3.4 m
2 m 2 m
PML
PML
y x
k
PEC
PMCGlass
H2O
Jx
Incident Intensity5.3 mW/m2
CPU Platform Dual Processor (3 GHz)
Quad Core Windows XP 64 Bit
32 GB Ram Time: 15 min per given
p
Axial Optical Force
vs. Field Polarization
p
Einc
k
TE
TM
Fz along this line
Glass
H2O
k
TrapTrap
k
Trap
TM polarization
Optical Force Analysis
Force Vectors in x-y Plane
Glass
H2O
TrappingPotential
-<We> J/m3
Glass
H2O
k
Trap
Rp = 50 nm
= 1000 nm
TE Analysis
TM Analysis -<We> J/m3TE Analysis
Einc
k
TE
TM
p
Trapping Force Analysis
kk
Force vs. Particle Size Force vs. Cone Separation
No Trapping for Large ParticlesScattering Force Dominates
Einc
k
TE
TM
d
p
TE Polarization = 635 nm
Rp = 50 nm
Axial Optical Force
vs. Field Polarization
p
Einc
k
TE
TM
Fz along this line
Glass
H2O
k
TrapTrap
k
Trap
Induced Electromagnetic Modes
Top View – Induced Ez Side View
E(t)
-z
x
Induced Ez
+ +
+
+ +
+
Top View
---
---
+ -
- + - +
+ -
= 635 nm
= 1000 nm
p
Einc
k
TE
TM
Fz along this line
Glass
H2O
2D Array of PillarsTE Trapping vs.
k
Rp = 100 nm
TE Analysis
k
Rp = 100 nm
Trap
Glass/Air
Glass/H2O
TE Analysis
Trap
p
Einc
k
TE
TM
Fz along this line
Glass
H2O
2D Array of RingsTE Trapping vs.
600 nm
200 nm
300 nm
k
Air Only
Trap
Rp = 100 nm
Rp = 100 nm
k
Glass/H2O
Trap
Optical trapping of neutral sub-wavelength particles can be achieved using local field enhancement near illuminated metallic nanostuctures.
Nano-trapping can be achieved with plane wave illumination.
Trapping force depends on particle size, , polarization and background permittivity.
Integration in Lab-on-Chip applications: Opto-fluidics
Summary and Conclusions