gold nanoparticles embedded in glassblair/t/ece6461/notes/intro.pdflocalized resonances/ -...

4

Gold nanoparticles embedded in glass

“Labors of the Months” (Norwich, England, ca. 1480).The ruby color is attributed to gold nanoparticles.

2pω

pω

3pω

++ -- ++ -- ++ --

+ + + +

+++

---

Bulkmetal

Metalsurface

Metal spherelocalized SPPs

Plasmon resonance positions in vacuumPlasmon resonance positions in vacuum

0=ε

1−=ε

2−=εdrudemodel

- - - -

drudemodel

Surface Plasmon PhotonicsSurface Plasmon PhotonicsOptical technology using- propagating surface plasmon polaritons- localized plasmon polaritons

Topics include:

Localized resonances/ - nanoscopic particleslocal field enhancement - near-field tips

Propagation and guiding - photonic devices- near-field probes

Enhanced transmission - aperture probes- filters

Negative index of refraction - perfect lensand metamaterials

SERS/TERS - surface/tip enhanced Raman scattering

Molecules and - enhanced fluoresencequantum dots

Also called:• Plasmonics• Plasmon photonics• Plasmon optics

Plasmon-PolaritonsWhat is a plasmon ?

• Compare electron gas in a metal and real gas of molecules

• Metals are expected to allow for electron density waves: plasmons

Strong local field

Metal

Dielectric

z

I

E

HNote: This is a TM wave

• Sometimes called a surface plasmon-polariton (strong coupling to EM field)

Surface plasmon

Bulk plasmon• Metals allow for EM wave propagation above the plasma frequency

They become transparent!

Local Field Intensity Depends on Wavelength

Long wavelength Short wavelength

z

I

z

I

D << λo

Characteristics plasmon-polariton • Strong localization of the EM field • High local field intensities easy to obtain

Applications: • Guiding of light below the diffraction limit (near-field optics)• Non-linear optics• Sensitive optical studies of surfaces and interfaces• Bio-sensors• Study film growth• ……

Optical Properties of an Electron Gas (Metal)Dielectric constant of a free electron gas (no interband transitions)

( ) ( ) ( ){ }Re expt i tω ω= −E E• Consider a time varying field:

• Equation of motion electron (no damping)2

2

dm edt

= −r E

• Harmonic time dependence ( ) ( ) ( ){ }Re expt i tω ω= −p p

• Substitution p into Eq. of motion: ( ) ( )2 2m eω ω ω− =p E

( ) ( )2

2

1em

ω ωω

= −p E• This can be manipulated into:

• The dielectric constant is:

• Dipole moment electron ( ) ( )t e t= −p r

22

2

dm edt

=p E

( )( )

22

2 20 0

11 1 1 pr

N Nem

ωωε χ

ε ω ε ω ω= + = = − = −

pE

ωrε

pω

6

Resonance conditions

)(1)(

2

γωωω

ωεj

p

+−=

Use a Drude model: Free electron (Lorenz model with no restoring force)

Bulk

Bulk Resonance condition : ε(ω)=0 ω=ωp.

Dispersion Relation for EM Waves in Electron Gas Determination of dispersion relation for bulk plasmons

( ) ( )2

22 2

,,r tt

cε ∂

= ∇∂E r

E rt

• The wave equation is given by:

• Investigate solutions of the form: ( ) ( ) ( ){ }, Re , expt i i tω ω= ⋅ −E r E r k r

2 2 2r c kω ε =

2

21 pr

ωε

ω= −• Dielectric constant:

22 2 2 2 2

21 pp c k

ωω ω ω

ω − = − =

ω

k

pω

No allowed propagating modes (imaginary k)

ckω =

2 2 2p c kω ω= +• Dispersion relation:

Note1: Solutions lie above light lineNote2: Metals: ħωp ≈ 10 eV; Semiconductors ħωp < 0.5 eV (depending on dopant conc.)

Dispersion Relation Surface-Plasmon PolaritonsSolve Maxwell’s equations with boundary conditions

• Maxwell’s Equations in medium i (i = metal or dielectric):

0iε∇ ⋅ =E 0∇⋅ =H 0µ∂

∇× = −∂HEt iε

∂∇× =

∂EHt

• At the boundary:

Metal

DielectriczE

H

, ,x m x dE E=

x

ym ydH H=m zm d zmE Eε ε=

• We are looking for solutions that look like:

( ) ( )0, ,0 expm ym xm zmH i k x k z tω= + −H

( ) ( ),0, expm xm zm xm zmE E i k x k z tω= + −E

( ) ( )0, ,0 expd yd xd zdH i k x k z tω= + −H( ) ( ),0, expd xd zd xd zdE E i k x k z tω= + −E

• Mathematically: z<0

z>0

ii iε

∂∇× =

∂EHt

Dispersion Relation Surface-Plasmon Polaritons

• Start with curl equation for H in medium i (as we did for EM waves in vacuum)

( ) ( )0, ,0 expi yi xi ziH i k x k z tω= + −Hwhere

( ) ( ),0, expi xi zi xi ziE E i k x k z tω= + −E

( ) ( ), , ,0, ,0,yi yizi xi zi xizi yi xi yi i xi i zi

H HH H H H ik H ik H i E i Ey z z x x y

ωε ωε∂ ∂ ∂ ∂ ∂ ∂

− − − = = − ∂ ∂ ∂ ∂ ∂ ∂

zi yi i xik H Eωε= −• We will use that: zm yi m xmk H Eωε= −

zd yd d xdk H Eωε= −

• E// across boundary is continuous: , ,x m x dE E=

zm zdym yd

m d

k kH Hε ε

=

• H// across boundary is continuous: ym ydH H=

Combine with: zm zdym yd

m d

k kH Hε ε

=zm zd

m d

k kε ε

=


Relations between k vectors

• Condition for SP’s to exist: zm zd

m d

k kε ε

=

• Relation for kx (Continuity E//, H//) : xm xdk k=

• For any EM wave:

zdk

zmkExample

1mε = −

1dε =z

z

22 2x zi ik k

cωε + =

22

sp x i zik k kcωε = = −

• Both in the metal and dielectric:

zm zd

m d

k kε ε

=

1/ 2

m dx

m d

kc

ε εωε ε

= +

Dispersion relation

homework

Example Air

SiO2true at any boundary

blair

Cross-Out


1/ 2

m dx

m d

kc

ε εωε ε

= +

Plot of the dispersion relation

• Last page:

• Plot dielectric constants

• Low ω: 1/ 2

limm

m dx d

m d

kc cε

ε εω ω εε ε→−∞

= ≈ +

• At ω = ωsp (when εm = -εd):

ω

rε

pωspωdε−

dε dielectricmetal

xk →∞

ω

k

spω

dkcω ε=

• Note: Solution lies below the light line


Dispersion relation plasma modes and SPP

• Note: Higher index medium on metal results in lower ωsp2

21 pm d

ωε ε

ω= − = − 2 2 2

p dω ω ε ω− = −2

2

1p

d

ωω

ε=

+ω = ωsp when:

Metal/air

Metal/dielectric with εd

1p

d

ωω

ε=

+

,SP Airω

, dSP εω

11

Propagation length

Methods of SPP excitationMethods of SPP excitation

nprism > nL !!

zx

E0θ

R

kxdε

mε

0ε

Excitation by ATRExcitation by ATR

Kretschmann configuration Otto configuration

zx

E0θ

R

kx

dεmε

0ε

total reflection at prism/metal interface-> evanescent field in metal-> excites surface plasmon polariton at

interface metal/dielectric medium

metal thickness < skin depth

total reflection at prism/dielectric medium-> evanescent field excites surface plasmon

at interface dielectric medium/metal

usful for surfaces that should not be damagedor for surface phonon polaritons on thick crystals

distance metal – prism of about λ

ATR: Attenuated Total Reflection

zx

θ

R

kSP,xdε

mε

0ε kphoton,x

< kSP,xkphoton,x

θ

R

kSP,x

kphoton,x

= kSP,xkphoton,x

no SPP excitation SPP excitation

Excitation by ATRExcitation by ATR

SPP excitation requires = kSP,xkphoton,x

Excitation by Kretschmann configurationExcitation by Kretschmann configuration

photon indielectric

photonin air

xk

ω

SPP dispersion

ck=ω

z

x

0θ

dε

mε0ε

0εωc

k =

ck ω

=

( )00 sin θεωc

kx =

( )00 sin/ θεω xkc=

0ω

( )0000

sin1

θεεεω cc

k m

m

x

=+

= Resonancecondition

0xk

1+=

m

mx c

kε

εω

Kretschmann configuration – angle scanKretschmann configuration – angle scan

0θ R

0θ

p-polarized

s-polarized-> no excitation of SPPs

illumination freq. ω0= const.

photonin air

kx

ω

0ω

R

0θ

21

Transmission EnhancementSingle hole

T. Thio et al., “ Optical transmission through a single sub-wavelength aperture,” Opt. Lett. 26, 1972 (2001).

Sample Parameters300 nm thick Ni filmFIB milling 5 nm resolution100nm AG film on one side30 nm Ag layer sputtered

Plan view

22

Extraordinary transmission through an array of holes

a0 = separationd= hole diametert=film thickness

23

Ebbesen experiment

24

TheoryNormal incidence

25

Hole period scaling

13

Localized surface plasmonresonance

Dipole surface plasmon is excited when a long-wavelength electromagnetic wave (λ>>d) is incident on a metallic sphere

Metallic sphere

EM wave

Plane-wave E-field E0e-i ω t

dλ

ε0εm

2

Plasmon-resonant nanoparticlesSurface plasmon (SP): collective excitation of conduction

electrons, using light at a resonant (visible to NIR) frequency

www.gold.org

Scattering from single Au nanospheres

Ag NPs (20−150 nm): λSP = 380−600 nm

Plasmon-enhanced extinction:ε = 109−1011 M-1 cm-1

Csca = 10-13−10-9 cm2

φsca = 0.04−0.90

Au NPs (20−150 nm): λSP = 520−660 nm

Lycurgus Cup, 4th century A.D.

(Ag-Au NP’s embedded in

glass)

Absorption: red Scattering: green

Brit

ish

Mus

eum

, Lon

don

14

Localized SPR frequency

00

0

23 EE

min εε

ε+

=

)()(1 222

22

22

2

γωωωγ

γωω

ε+

−+

−= ppm j

Field inside the metal particle

Complex function

Simple Drude model for a metal

ωp is the plasma frequency , the dielectric function has a negative real part for ω < ωp.

Real part of denominator vanishes at the SPR: 12 0 +=

εω

ω pSPR

nanopar&cle sca,ering and ex&nc&on

par&cle polarizability

ex&nc&on cross-‐sec&on (units of area)

total sca,ering cross-‐sec&on (units of area)

€

α = 4πa3 εm −ε oεm + 2ε o

a = particle radius ε o = surrounding medium

€

Cext =2πλImaginary α{ }

€

Csca =16π

2πλ

⎛

⎝ ⎜

⎞

⎠ ⎟ 4

α 2

Kriebig and Vollmer, Optical Properties of Metal Clusters, c.1995.

Physical description of plasmons (cont’d)Electrodynamic Mie TheoryCan calculate dipolar optical response with great accuracy,especially if performed under “quasi-static” conditions(valid when particle size is less than 30 nm)

1240 62

0

413

310

Generalized Mie Theory:Can calculate approximate optical response for metal nanoparticles of all shapes and sizes; accounts for higher-order effects such as phase retardation, quadrupolar resonances, etc.

Calculated plasmon response from spherical Au nanoparticles in H2O:

Yguerabide, Anal. Biochem. 1998, 262, 137.

Calculated response (extinction) from metal nanoparticles (in air):

eV-to-λ (nm)conversion: eV

1239=λ

λ (nm)

6

Size effects on localized SPRs

Surface scattering of oscillating electrons: plasmon lineshape (Γ) broadens with 1/R

Calculated plasmon response from spherical Ag nanoparticles in H2O: Yguerabide, Anal. Biochem. 1998, 262, 137.

Phase retardation: redshift and broadening of λSP for particles greater than LE, the electron mean free path (40-50 nm)

Higher-order plasmon resonances: increase in probability with larger particle size (also a function of LE)

Dipolar mode

Quadrupolar mode

Octupolar mode

6

15

SPR – refinements – particle shape and core/shell

• Gold and silver metal particles –shape dependence

)3(21

21

)3( |)(|)( χωγωγχ =eff

• Core-shell particles have larger enhancement

Ellipsoidal shapes

M&M – metal shell creates resonance in the coreεs

εc

Γ+Γ−

=)()1(

)(11

11 ωεε

εωγmii

−−+++−+−++

=))((2)2)(2()]/()2)(()2[()(

11

1111 εεεεδεεεε

εεεεεεδεεεωγ

sscscs

ssscsc

εm

16

Nanoshells

17

Absorption and Field enhancementCdS/Ag

core-shell ratio of 0.7The field magnitudes are scaled to the asymptotic applied field value. The surface plasmon resonance appears near a wavelength of 600 nm.

18

Heterostructured nanoparticles

core

Shell

Metal shell: surface plasmon resonance shifts by more than 500 nm observed. Enhanced nonlinear effects and intrinsic optical bistability observed.

PRB 47, 1359 (1993); PRB 50, 12052 (1994).

Exp.: A gold sulfide sample is decomposed into gold particles. The transformation begins at the surface.Numbers are time lapses.

19

Tunability

12

SP modes as a function of aspect ratio:Link and El-Sayed, J. Phys. Chem. B 1999, 103, 3073

Transverse SP

Longitudinal SP(λmax)

Au

LSP

TSP

Au NRs: Tunable resonances in the NIR

Anisotropic metal nanoparticles: Au nanorods

Attenuation is minimized between 750 nm and 1.3 μm

H2 O

1 0 - 2

1 0 2

1

1 0

.2 .4 .6 .8 1 .0 2 . 4 . 6 . 8 .

H b O 2-1

Abs

orpt

ion

Coe

ffici

ent

Wavelength (µm)

Absorption Transmission Absorption

1 0 - 1

“Biological window” in tissue at NIR wavelengths:

Anisotropic metal nanoparticles: Au nanorods

13

Seeded growth using micellar surfactants (CTAB):

Sau and Murphy, Langmuir 2004, 20, 6414.Zweifel and Wei, Chem. Mater. 2005, 17, 4256.

AgNO3, CTAB

AuCl4, ascorbic acid15-60 min

3-nm Au particle seeds

Two-stage growth kinetics: effect on LPR wavelength

Wavelength (nm)400 500 600 700 800 900 1000

Nor

mal

ized

O.D

.

1x wash, 0 d1x wash, 1 d2x wash, 0 d2x wash, 1 d

1st growth stage (fast): dumbbell-shaped NRs(stabilized after Na2S)

2nd growth stage (slow):Cylindrical NRs

Au avg. width: 15-20 nm

avg. length: 40-60 nm

Synthesis of NIR-resonant Au nanorods

14

Nanostars (seeded growth from Au NPs)

Pentagonal bipyramids (decahedra)

Nanoshells(SiO2@Au)

Nanocages (growth on Ag nanocubes, with galvanic displacement)

Nanoprisms (by nanosphere lithography)

Haynes and van Duyne, J. Phys. Chem. B 2001, 105, 5599.

Kelly et al, J. Phys. Chem. B2003, 107, 668

Sanchez-Igleisias et al,Adv. Mater. 2006, 18,

2529

Lal et al., Acc. Chem. Res.2008, 41, 1842

Siekkinen et al, J. Am. Chem. Soc. 2006, 128, 14776

Nehl, Liao, and Hafner, Nano Lett. 2006, 6, 683

Other anisotropic Au nanoparticles

Local field factors increase nonlinearly as a function of particle diameter–spacing ratio (γ)

Size of ensemble, unit particle size are also important factors in EM enhancement

EM field factors in NP assemblies:

Calculation of G = (E/E0)4 in Ag NP dimer, as a function of interparticle separation

Xu et al, Phys. Rev. E 2000, 62, 4318.

λex=514.5 nm; 2R =90 nm, S= 1 or 5 nm (Ag)

GEM

S = 1 nm

S = 5 nm

Local EM field factors (E/E0): extends for several nanometers from NP surface, in direction of LSPR mode

Origin of plasmon-amplified signals in surface-enhanced Raman scattering (SERS) and other optical emissions

Plasmon-enhanced field effects

7

A. Surface-enhanced Raman scattering (SERS)

N

R'

H

R

nanostructured Ag and Au surfaces(roughness ~ 10-200 nm)

200 400 600 800 1000 1200 1400

cm -1

analyte

hν1 hν2

Raman spectrum

• Label-free chemical sensing• Multiplexing capabilities• Water is Raman-silent

• relationship between nanostructure and activityoften not well-defined

• SERS-active substrates are easy to make, but can be tricky to reproduce

Plasmon-enhanced emissions

8

SERS activity is strongly correlated with local electromagnetic (EM) field factors

“Hot spots” can be found at edges and tips of anisotropic NPs, but can be even stronger in gaps between closely spaced metal nanostructures

Liu et al. Adv. Mater. 2005, 17, 2683.

SERS-active “nano-crescents” Self-assembled Au nanoparticle arrays

Wei et al, ChemPhysChem2001, 2, 743.

Genov, Sarychev, Shalaev, Wei, Nano Lett. 2004, 4, 153.

λex=647 nm; γ = 5 or 10 (Au)2D array of 87-nm Au NPs

“Hot Spots” in SERS-active substrates

9

B. Surface-enhanced fluorescence (SEF)Highly sensitive to distance between fluorophore and metal surface: SEF also relies on local EM field factors, but excited states can be quenched by back-electron transfer

Multilayers of phospholipid or BSA−biotin/avidin over Ag NPs, then coated with fluorophore

Fluorescence intensity of biotin−FITC on top of (1) six, (2) four, and (3) two monolayers formed by alternating avidin and BSA−biotin.

Nanometric coatings for optimizing SEF (up to 20-fold increase in fluorescence)

Sokolov, Chumanov, and Cotton, Anal. Chem. 1998, 70, 3898.

No SEF


10

C. Förster resonance energy transfer (FRET)

Energy transfer mediated by overlap between emission and absorption (donor−acceptor) bands; D−A distance <10 nm

Dye-doped Ag@SiO2 core-shell NPs

Plasmon-enhanced FRET: greater efficency and range

Lessard-Viger et al, Nano Lett. 2009, 9, 3066.Wang and Wang, Integr. Biol. 2009, 1, 565

Shell=7 nm 13 nm 23 nm

D A


11

A. Resonant light scattering: Darkfield microscopy

Aaron et al, Opt. Express 2008, 16, 2153.

Cross-polarized scattering: a novel method of noise reduction for anisotropic NP labels

Ag nanoparticles of variable size and shape

Plasmon-resonant NPs used as biological imaging labels must also compete with other scatterers.

Spherical NP

Stellated NP 90° scattering (from incident polarization)

A431 cells with anti-EGFR labeled nanostars

Linear pol. Cross pol.

no NPs

Imaging: Metal NPs as optical contrast agents

12

B. Multiphoton excitation

400 500 600 700 800 9000.0

0.4

0.8

1.2

0.0

0.2

0.4

0.6

0.8

I PL (a

.u.)

Abso

rban

ce (a

.u.)

Wavelength (nm)

sp-hole relaxation after 2-photon absorption

2ν ν’5d

6sp

TPL intensity vs. Au NR absorption:

Wang et al. PNAS 2005, 102, 15752.

Au

Au

fs-pulsed

laser excitation

TPL of Au NRs on glass slide

1

2

pol.

Two-photon excited luminescence (TPL) from Au nanorods


13

(a) TPL image of Au NRs (green) internalized by KB cells after a 5-hour incubation (linescan = 75 µm).

(b) Intensity profile across yellow linescan in (a); high SNR provided by TPL contrast.

a b

Huff et al, Nanomedicine 2007, 2, 105.

In vivo TPL imaging of Au NRs flowing through blood

vessel in mouse ear

In vitro TPL imaging of Au NR uptake by KB cell: single-particle sensitivity

Wang et al. PNAS 2005, 102, 15752.

Multiphoton imaging has very low autofluorescence

14

SERS reporter label: Malachite Green

Targeted in vivo delivery of SERS labels to tumor in nude mouse model:

in vitro detection of labeled SERS tags: compares well with fluorescence imaging

Qian et al, Nat. Biotechnol.2008, 26, 83.

C. Au NPs as SERS tags


15

Optical coherence tomography

200 um

tissue surface

Oldenburg et al, J. Mater. Chem. 2009, 19, 6407.Eghtedari et al, Nano Lett. 2007,7, 1914.

Relatively high loadings of Au NPs are still required to generate sufficient contrast in tissue for these imaging modalities.

Photoacoustic tomography

PAT of Au NRs within nude mouse (before and after injection)

OCT contrast by Au NRs in human breast carcinoma tissue

After Au NR injection

D. Other optical modalities for biomedical imaging


17Govorov and Richardson, Nano Today 2007, 2, 30.

Absorbed light is mostly converted into heat

abs

p

ETmc

∆ =Estimation of surface temperature on Au NP:

0

( )4

NPV QT rk rπ

∆ =

Eabs =absorbed photon energym =mass of Au NPcp = heat capacity of Au

ΔT for 5-nm Au sphere =15 K at LSPR saturation

Estimation of heat transfer to environment of Au NP:

1/r dependence

VNP = volume of NPQ = heat of NPk0 = thermal conductivity of mediumr = distance from surface

Photothermal activity of metal nanoparticles

18

((( )))

Link and El-Sayed, Int. Rev. Phys. Chem. 2000, 19, 409.Pitsillides et al, Biophys. J. 2003, 84, 4023.

10-15 (fs) 10-12 (ps) 10-9 (ns) 10-6 (μs) 10-3 (ms) 100 (s)

Au

1. Electron thermalization;transient plasmon bleaching

2. Electron-phonon collisions;local heating by 100s of °C

Au

3. Cavitation dynamics:microbubble expansion

Au

4. Microbubble collapse; acoustic energy released

Superheating can lead to mechanical release of energy

Timescale of photothermal response, induced by pulsed laser excitation:

Photothermal activity of metal nanoparticles

19

Internalized Au NRs

81 s scan, cw mode:Laser power = 6 mw; fluence = 24 J/cm2

Membrane-bound Au NRs on tumor cells

6mw CW

before

10 µm

after, w/ EB stain

Threshold fluence for hyperthermic damage (blebbing)

is 10X lower or more when nanorods are localized on cell

membranes

before after, w/ EB stain

Tong et al, Adv. Mater. 2007 19, 3136.

81 s scan, cw mode:Laser power = 60 mw; fluence = 240 J/cm2

before after, w/ EB stain

81 s scan, fs-pulsed mode:Laser power = 0.75 mw; fluence = 3 J/cm2

Photothermolysis of tumor cells mediated by Au NRs targeted to cell membranes

Why nanophotonics needs plasmons?

Courtesy of M. Brongersma

31

• Surface plasmon resonance• Continuous films

– Propagating mode couples to the surface and propagates

-Reflection dip at the phase matching angle for coupling

• Disontinuous films– Local field resonance condition

• Applications• Bio/chem assays• Cancer therapy• Photonic waveguides

Summary

32

References • BookP. N. Prasad, Nanophotonics, Wiley-Interscience (2004) Optics Express, Volume 12, Issue 16, (9 August 2004), Focus Issue: Extraordinary

Light Transmission Through Sub-Wavelength Structured SurfacesMetal particles: shape and core-shell effectsM. J. Bloemer et al., “Broadband Waveguide Polarizers Based On The Anisotropic

Optical Constants Of Nanocomposite Films,” J. Lightwave Tech. 14, 1534 (1996).

H.S. Zhou et al., “The Controlled Synthesis and Quantum Size Effect in Gold Coated Nanoparticles,” Phys. Rev. B 50, 12052 (1994).

J.W. Haus et al., “Enhanced Optical Properties of Metal-coated Nanoparticles,” J. Appl. Phys. 73, 1043 (1993).

J.W. Haus et al., ”Intrinsic Optical Bistability for Coated Particles,” Phys. Rev. A 42, 5613 (1990).

A. Neeves and M. Birnboim, Opt. Lett. 13, 1087 (1998).J. Haus, H.S. Zhou, S. Takami, M. Hirasawa, I. Honma, and H. Komiyama, J. Appl.

Phys. 73, 1043 (1993).R. Eychmuller, A. Mews, and H. Weller, Chem. Phys. Lett. 208, 58 (1993).H. Zhou, I. Honma, H. Komiyama, and J. Haus, J. Phys. Chem. 97, 895 (1993)H.S. Zhou, I. Honma, H. Komiyama, and J.W. Haus, Phys. Rev. B 50, 10210 (1994).R. Neuendorf, M. Quinten, and U. Kreibig, J. Chem. Phys. 104, 6348 (1996).

33

ReferencesV.M.Shalaev, Nanoscale Linear and Nonlinear Optics, eds: M. Bertolotti and C.Sibilia, AIP p239-241 (2001).S. Oldenburg, R. D. Averitt, S. Westcott, and N. J. Halas, Chem. Phys. Lett. 288, 243

(1998).Y. Sun, Y. Xia, Anal. Chem. 74, 5297 (2002).Attridge, J.W.; Daniels, P.B.; Deacon, J.K.; Robinson, G.A.; Davidson, G.P. (1991)

Sensitivity enhancement of optical immunosensors by the use of a surface plasmonresonance fluoroimmunoassay, Biosens. Bioelectron. 1991; 6(3): 201-214

Bain C.D., Whitesides G.M. (1989) Modeling organic surfaces with self-assembled monolayers, Adv. Mater. 4: 110

K. Lance Kelly, Eduardo Coronado, Lin Lin Zhao, and George C. Schatz, J. Phys.Chem. B 107, 668-677 (2003).E. Prodan, C. Radloff, N.J. Halas and P. Nordlander, Science 302, 419-422 (2003).E.Prodan, P. Nordlander, Nano Lett. 3, 543-547 (2003).M.Brongersma, Nature Materials 2, 296, (2003).C.Loo, A. Lin, L. Hirsch, Min-Ho Lee, J. Barton, N. Halas, J. West, R. Drezek,Technology in Cancer Research and Treatment 3, 33-40 (Feb. 2004).E. Prodan and P. Nordlander,, J. Chem. Phys. 120, 5444-5454, (2004).

Websiteshttp://shay.ecn.purdue.edu/~ece695s/http://lanp.rice.edu/Plasmonics/publications.phphttp://www-ece.rice.edu/~halas/pubs.html

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