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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.

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Plasmon assisted nanotrapping l.jpg
Plasmon Assisted Nanotrapping

E. P. Furlani, A. Baev and P. N. Prasad

The Institute for Lasers, Photonics and Biophotonics University at Buffalo, SUNY


Overview l.jpg
Overview

  • Introduction

  • Applications

  • Experimental Results

  • Modeling Nanotrapping Systems

  • Summary


Optical trapping laser tweezers l.jpg
Optical Trapping – Laser Tweezers

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).

D. G. Grier Nature 424 2003


Plasmonic based optical nano trapping l.jpg

+-

+-

+-

+-

Plasmonic-based Optical Nano-trapping

Locally enhanced field near illuminated metallic nanostructures creates gradient optical force that traps nanoparticles.

Einc(t)

DielectricNanoparticle

p

Well suited for trapping sub-wavelength metallic or dielectric particles.

Potential for integration with Lab-on-Chip systems (opto-fluidics).

Gold Nanocones


Surface plasmon resonance spr and localized spr lspr in metallic nanostructures l.jpg

E

Strong Local Field

d

- - -

- - -

- - -

+ + +

+ + +

m

H

.

E(t)

- - -

+ + +

+ + +

- - -

Surface Plasmon Resonance (SPR)and Localized SPR (LSPR) in Metallic Nanostructures

Plasmon: Quantized charge density wave in free electron gas.

SPR: Surface plasmons confined to metal/dielectric interface.

Wave vectors

LSPR: Resonant scattering modes in sub-wavelength metallic nanoparticles


Motivation for lspr nanotrapping l.jpg
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:integratedoptical particle manipulation/separation for BioMEMS, Lab-on-a-Chip systems.


Slide7 l.jpg

- - -

+ + +

+ + +

- - -

Local Field Enhancement Metallic Nanoparticles

E(t)

d

mp

P(t) = E(t)

Optical Absorption - Scattering Local Field Enhancement

Absorption frequency/bandwidth depend on particle size, shape, composition and surrounding media etc.


Analytical dielectric function for au nanostructures l.jpg
Analytical Dielectric Function for Au Nanostructures

+-

+-

+-

+-

Experimental and analytical dielectric values vs. 

Einc

Analytical Dielectric Function for Au used in Analysis*

*P. G. Etchegoin et al. J. Chem. Phys. 125, 164705 (2006)


Optical trapping of sub wavelength neutral particles l.jpg
Optical Trapping of Sub-Wavelength Neutral Particles

Force on Dielectric Nanoparticle caused by Local Field Gradient produced by Illuminated Metallic Nanoparticles

Dielectric Nanoparticle

Metallic Nanostructures


Slide10 l.jpg

Fabricated Metallic Nanostructures

Nano-cone Array

Nano-Ring Array

Nano-Pillar Array

T. Atay et al.,Nano Letters 4 2004

J. Aizpurua et al., PRL 90 2003


Experimental results l.jpg

90 nm

120 nm

Experimental Results

Optical trapping of nanoparticles using taperedmetallic nanopillars

1 m

Collaboration with A. N. Grigorenko et. al, Nanometric optical tweezers based on nanostructured substrates, U. Manchester UK


Optical trapping of microbubbles on nanostructured substrate l.jpg

90 nm

120 nm

Optical Trapping of Microbubbleson Nanostructured Substrate

A.R. Sidorov et al.Optics Communications 278 (2007)


Enhanced optical trapping au nanoparticle array l.jpg

Moving Dielectric Sphere

Trapped Dielectric Sphere

Array of Au Nanostructures

Enhanced Optical Trapping Au Nanoparticle Array

X. Maio and L. Y. Lin, Opt. Letters. 32 2007,also unpublished work 2008


Plasmonic trapping of cells l.jpg

Array of Au Nanostructures

Plasmonic Trapping of Cells

Single Yeast Cell Trapped in Square (other cells moving at constant speed)

Optical intensity required for stable trapping of single yeast cell is 78.8 W/m2

Moving Cells

Trapped Cell

X. Maio and L. Y. Lin, IEEE J. Sel. Topics Quant. Elec. 132007


Modeling optical nanotrapping l.jpg
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 l.jpg
Optical Force on a Dielectric Nanoparticle

Einc(t)

p

p

+-

+-

+-

+-

d

mp()

mp()

Time-averaged Optical Dipolar Force Fopt is a function of several variables: , p, mp(),d,and the geometry, composition and coupling of metallic nanostructures.


Trapping and scattering force components l.jpg
Trapping and Scattering Force Components

Trapping Potential Vtrap:


Full wave time harmonic analysis array of nanopillars glass substrate covered with h2o l.jpg
Full-Wave Time-Harmonic Analysis(Array of Nanopillars: Glass Substrate covered with H2O)

k

y

x

p

k

z

y

x

Computational Domain

PML

H2O

PEC

3.4 m

Glass

2 m

PMC

PML

2 m

2 m

Symmetry Boundary Conditions: PEC, PMC


Computational model l.jpg
Computational Model

y

x

p

k

z

y

x

Surface current Jx BC chosen to produce plane wave: Ex = 2106 V/m. FEA Model: 43,904 cubic vector elements with 838,485 degrees of freedom.

Computational Domain

CPU Platform Dual Processor (3 GHz)Quad Core Windows XP 64 Bit32 GB Ram Time: 15 min per given 

Jx

PML

Incident Intensity5.3 mW/m2

H2O

PEC

3.4 m

Glass

PMC

PML

2 m

2 m

Symmetry Boundary Conditions: PEC, PMC


Axial optical force vs field polarization l.jpg
Axial Optical Forcevs. Field Polarization

Trap

Einc

TE

TM

k

k

TM polarization

Trap

k

p

Fz along this line

H2O

Glass


Optical force analysis l.jpg

Rp = 50 nm

 = 1000 nm

Einc

TE

Trap

TM

k

p

k

Optical Force Analysis

TE Analysis

TM Analysis

-<We>J/m3

-<We>J/m3

TE Analysis

TrappingPotential

Force Vectors in x-y Plane

H2O

H2O

Glass

Glass


Trapping force analysis l.jpg

Einc

TE

TM

k

d

p

k

k

Trapping Force Analysis

TE Polarization = 635 nm

Force vs. Cone Separation

Force vs. Particle Size

Rp = 50 nm

No Trapping for Large ParticlesScattering Force Dominates


Axial optical force vs field polarization23 l.jpg
Axial Optical Forcevs. Field Polarization

Trap

Einc

TE

TM

k

k

Fz along this line

Trap

H2O

Glass

k

p


Induced electromagnetic modes l.jpg
Induced Electromagnetic Modes

 = 635 nm

-+

-+

Top View

+-

+-

-

-

-

-

-

-

+ + +

+ + +

 = 1000 nm

Side View

Top View – Induced Ez

x

Induced Ez

E(t)

-z


Slide25 l.jpg

Rp = 100 nm

Trap

Einc

TE Analysis

k

Glass/Air

TE

TM

k

Rp = 100 nm

Trap

TE Analysis

Glass/H2O

k

p

2D Array of PillarsTE Trapping vs. 

Fz along this line

H2O

Glass


Slide26 l.jpg

Rp = 100 nm

Trap

Einc

Air Only

TE

TM

k

k

k

Rp = 100 nm

Trap

Glass/H2O

p

2D Array of RingsTE Trapping vs. 

Fz along this line

300 nm

H2O

200 nm

600 nm

Glass


Summary and conclusions l.jpg
Summary and Conclusions

  • 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