Surface-Plasmon Sensors

Surface-Plasmon Sensors

Seok Ho Song

Physics Department in Hanyang University

Dongho Shin, Jaewoong Yun, Kihyong Choi

Gwansu Lee, Samsung Electro-Mechanics

Dispersion relation of surface plasmons

Sensors based on surface plasmon resonance (SPR) Localized surface plasmon resonance (LSPR) sensors Surface-plasmon-polaritons waveguide sensors

Contents

Surface plasmons

at dielectric-metal boundaries

Dispersion relation of surface plasmons

2 2

1 )

( ω

ω ω

ε

= −

m d x

m d

k c

ω ε ε

ε ε

= +

• Plot of the dielectric constants:

• Plot of the dispersion relation:

d p sp

d m

ω

ω ε

ω ε

ε

= +

≡

∞

→

⇒

−

→

•

1 , k

, When

x

2 2 2 2

) 1

(

) (

p d

d p sp

x

k c

k ε ω ω

ε ω ω ω

− +

= −

=

Surface plasmon dispersion relation:

2 / 1

⎟⎟ ⎠

⎜⎜ ⎞

⎝

⎛

= +

d m

d m

x

c

k ε ε

ε ε ω

ω

ω

d p

ε ω

+ 1

Re k _x

real k

real k

imaginary k

real k

real k

imaginary k

d

ck

ε

Bound modes Radiative modes

Quasi-bound modes

Dielectric:

ε_d

Metal: ε_m= ε_m^'+ ε_m^"

x z

(ε'

> 0)

(−ε

< ε'

< 0)

(ε'

< −ε

)

2 2 2 2

p c kx

ω

ω

Surface plasmon dispersion relation

2 1/ 2 i zi

m d

k c

ε ω

ε ε

⎛ ⎞

= ⎜ ⎝ + ⎟ ⎠

Plasma resonance in summary

Excitation of surface plasmons

Brewster condition?

x

BREWSTER’S ANGLE BREWSTER’S ANGLE

Figure 2.5 Reflection and transmission coefficients as a function of incident angle for air to glass interface.

Brewster angle only for TM pol.

= 0 ; when θ

+ θ

= 90

(Note)

Brewster’s condition is a consequence of impedance matching with reference to the vertical direction Æ

From Snell’s law : n

sin θ

= n

sin θ

→ η

sin θ

= η

sin θ

x

x 2

1

η

η = : Brewster’s condition

Åθ₁ + θ₂= 90^o For TM :

No reflection

Does the condition of the surface plasmon resonance match the Brewster’s condition?

Does the condition of the surface plasmon resonance match the Brewster’s condition?

θ

= θ

!!!

x

x 2

1

η

η =

Åθ₁ + θ₂= 90^o

ε

ε

θ

θ

metal

E E = 0

ε

θ

1

sin

sin

,

sin

sin

n θ = n θ n θ = n θ

Snell’s law:

2 2

3 2 1

3 3

2

2 3

2 2

1 3

3 3 1

2 2 1 2

3 3 2 2

1 2

sin sin cos

1 sin 1 sin

sin

n n

n n

n

n n

n n n

n n n

n n

θ θ θ

θ θ

θ

= =

⎛ ⎞

= − = − ⎜ ⎟

⎝ ⎠

⇒ =

+

( )

( )

2 2

1 2 1 2

3 0 3 2 2

1 2 1 2

3 0 3

sin

sin

n k n n

c n n c

n k k

ε ε

ω ω

θ ε ε

θ

⎛ ⎞ ⎛ ⎞

= ⎜ ⎟ ⎝ ⎠ + = ⎜ ⎟ ⎝ ⎠ +

≡

1 2

1 2

k sp

c

ε ε ω

ε ε

= ⎜ ⎟ ⎛ ⎞ ⎝ ⎠ +

when θ₁ + θ₂ = 90^o

Brewster’s condition Æ Matching of characteristic wave impedance at normal direction

Let’s consider the light propagation in reciprocal direction

Sensors based on surface plasmon resonance (SPR)

Surface plasmon resonance (SPR) sensor

Concept of SPR Biosensing

Re{ } Im{ }

M D

M D

c

ω ε ε

β β β

ε ε

= = +

+

Re{ } β ≅ ⋅ k n k: free-space wavenumber

The propagation constant k of the SPW can be determined by measuring changes in one of these characteristics.

angular modulation intensity modulation

wavelength=682nm Angle of incidence 54

Concept of SPR Biosensing

• Spatially-filtered, expanded, p-polarized HeNe laser

beam illuminates the gold sample through a prism coupler.

• Reflected light from the

gold surface, containing the SPR image, is monitored with a CCD camera.

• The angle of incidence can be changed by rotating the entire sample assembly.

A.J. Thiel et. al., Anal. Chem. 69 (1997), pp. 4948–4956.

SPR imaging

2D and 3D Images of ssDNA

•Shows the 5 spots of self

assembled thio-oligonucleotide DNA probes immobilized on the gold surface

•Color variation indicates

variation in the thickness of the self assembled monolayer

(SAM)

•R. Rella, et al. Biosensors and Bioelectronics. 20 (2004), pp.1140-1148.

(from propagating to localized plasmons)

Localized surface plasmon resonance (LSPR)

A novel ultrahigh-resolution surface plasmon resonance biosensor with an Au nanocluster-embedded dielectric film

Biosensors and Bioelectronics 19 (2004) 1465–1471 The detection performance of conventional surface plasmon resonance (SPR) biosensors is

limited to a 1 pg/mm²surface coverage of biomolecules.

Au nanocluster-enhanced SPR biosensor provides the potential to achieve an ultrahigh-resolution detection performance of approximately 0.1 pg/mm²surface coverage of biomolecules.

Au nanoclusters 4 nm size

6 nm interval

GAS

DNA

Localized surface plasmon resonance (LSPR)

Sensing using Nanoshells

Waveguide sensors based on

long-range surface plasmon polaritons (LR-SPPs)

Metal strips guiding surface plasmon polaritons

metal strip

dielectric

thickness ~ 10 nm

surface plasmon-polaritons

frequency

in-plane wavevector

Long-Range SPP:

weak surface confinement, low loss

Short-Range SPP:

strong surface confinement, high loss

Coupling of Surface Plasmon Polaritons

LR-SPP and SR-SPP on thin metal films

Dispersion curves of a metal slab

0 50 100 150 200

1.5 1.6 1.7 1.8 1.9 2.0

a_b s_b

β r/k 0

thickness (h : nm)

0 50 100 150 200

10^-7 10^-6 1x10^-5 1x10^-4 10^-3 10^-2 10^-1

10⁰ a_b

s_b

β i/k 0

thickness (h : nm)

-3 -2 -1 0 1 2 3

-1.0 -0.5 0.0 0.5 1.0

H y(a.u.)

length (μm)

ab

s_b

Field Profile Symmetric Mode

Anti-Symmetric Mode

Real part of Effective index Imaginary part of Effective index

Field profile of slab SPP modes)

-4 -2 0 2 4

-1.0 -0.5 0.0 0.5 1.0

length (μm)

h=20nm h=40nm h=100nm h=200nm

H y(a.u.)

-4 -2 0 2 4

0.0 0.2 0.4 0.6 0.8 1.0

H y(a.u.)

length (μm)

h=20nm h=40nm h=100nm h=200nm

-0.2 -0.1 0.0 0.1 0.2

-1.0 -0.5 0.0 0.5 1.0

h=20nm h=40nm h=100nm h=200nm

H y(a.u.)

length (μm)

-0.2 -0.1 0.0 0.1 0.2

0.0 0.2 0.4 0.6 0.8 1.0

length (μm)

H y(a.u.)

h=20nm h=40nm h=100nm h=200nm

Symmetric Mode

Anti-Symmetric Mode

Field enhancement at the boundary

Æ Sensitive to environment

Dispersion curves of a finite-width strip

0 50 100 150 200

1.50 1.52 1.54 1.56 1.58 1.60 1.62 1.64

β r/k 0

aa_b^o ss_b⁰

thickness of metal(nm)

0 50 100 150 200

10^-7 10^-6 1x10^-5 1x10^-4 10^-3 10^-2

β i/k 0

aab o

ssb 0

thickness of metal(nm)

0 5 10 15 20 25 30

1.500 1.502 1.565 1.570 1.575

slab(20nm) β r/k 0

aab o

ss_b⁰

metal stipe width(μm)

5 10 15 20 25 30

1x10^-5 1.3x10^-2 1.4x10^-2

slab(20nm)

metal stipe width(μm)

aa_b^o ssb

0

β i/k 0

Metal Thickness Metal Stripe width

Long-Range Surface Plasmon Polaritons Waveguide LongLong--Range Surface Plasmon Polaritons WaveguideRange Surface Plasmon Polaritons Waveguide

SiO2 Au

~ 20nm

~ 5um

LR-SPPs W/G Structure

mode SS

Mode profile of

Best measurements:

- Attenuation: 3.2 dB/cm - Coupling to SMF: < 0.2 dB

LR-SPPs Waveguide Devices

Optical modulator & switch

Sergey I. Bozhevolnyi Group (Denmark)

Optical add/drop filter

Bragg grating filter Pierre Berini Group (Canada) Vertical directional coupler

Seok Ho Song Group (Korea)

optical Sensor ?

LR-SPP waveguides

Long-Range Surface Plasmon Polaritons Waveguide Sensor Long-Long-Range Surface Plasmon Polaritons Waveguide SensorRange Surface Plasmon Polaritons Waveguide Sensor

Metal waveguide

1.330 1.331 1.332 1.333 1.334 1.335 1.336 0

50 100 150 200 250 300 350

Intensity (uW)

Refractive index of water

Reference arm Sensing arm If something is changed

Æ Mode of LR-SPP & output signal is changed

Output signal

- Air or water background - Polarizing waveguide

- Higher waveguide sensitivity - Higher waveguide loss

: Hybrid waveguide structure - Added functionality

: In situ heating or electric field

Metal waveguide sensor Dielectric waveguide sensor

- Air or water background - Non polarizing waveguide - Low waveguide sensitivity - Lower waveguide loss - No added functionality

LR-SPP Waveguide Sensor

Metal waveguide

Reference arm Sensing arm

If something is changed

Æ Mode of LR-SPP is changed

ÆThe output signal (Interferometer signal) is changed

LR-SPP Waveguide Sensor

Region 1 Region 2

Region 1 Cross Section

Region 2 Cross Section

~ 1.47( )

nclad dielectric

em

, d

ε ε

, d

~ 1.33( ) n

water

em

, d

ε ε

, d

Liquids

(ex. Bio-molecules)

LR-SPP Waveguide on a membrane

1.3305 1.3310 1.3315 1.3320 1.3325 1.3330

20 40 60 80 100 0

1 2 3 4 5 6

thickness of membrane (nm)

Propagation loss (dB/mm)

N eff

2 2

1.55

, 20 , 5

1.33 , 1.45

m Au Au

c em

m

d nm w m

λ μ

ε ε μ

ε ε

=

= = =

= =

Region 2 (sensing region)

0 2 4 6 8 10 12 14 16 18 20 22 1.3314

1.3315 1.3316 1.3317 1.3318

dem=50nm

N sens

thickness of d

a(nm) εc

em,dem

ε

Au,dAu

ε

, (variable)

a da

ε

1.330 1.332 1.334 1.336 1.338 1.340 1.330

1.332 1.334 1.336 1.338 1.340 1.342

d_em=50nm

N sens

index(n_c)

1.91 10 /

a

n nm

d

∂

= ×

∂

Sensitivity of LR-SPP Waveguide Sensor

0.99465

eff c

n n

∂ =

∂

Index change by thermal/density

Index change by thichness

Almost 1 (varialbe)

εc em,dem

ε

Au,dAu

ε

Sensitivity of LR-SPP sensor : an embedded structure

εc em,dem

ε

Au,dAu

ε εa^,da^(variable)

2 4 6 8 10 12 14 16 18 20 22

1.3328 1.3329 1.3330 1.3331 1.3332

dem=100nm

Effective Index, N eff

Thickness of d

a [nm]

1.92 10 /

a

n nm

d

∂

= ×

∂

εc em,dem

ε ε^Au,dAu

, (variable)

a da

ε

4 6 8 10 12 14 16 18 20 22 24

1.3386 1.3387 1.3388 1.3389 1.3390 1.3391 1.3392 1.3393

d_em=100nm

Effective Index, N sens

Thickness of d

a [nm]

3.6 10 /

a

n nm

d

∂

= ×

∂

Sensitivity of LR-SPP sensor : embedded thickness

Increase in embedded layer thickness

Reduction of mode size

Increase in E-Field

Stronger interaction

Better sensitivity

SiO2(1.47) Air(1.0) SiO2

water Cross section Cross section

metal 5 mμ

20nm 2

100nm SiO2

1

1000 mμ

In Out

1000 mμ 500 mμ 500 mμ 2000 mμ 500 mμ 500 mμ 1000 mμ 40 mμ

1

2

Intensity modulation from an interferometer

membrane 1

membrane 2 Metal

Receptor

dielectric dielectric substrate

If a detector has 0.1 uW sensitivity, 3 pm thickness variation can be detectable.

If a detector has 0.1 uW sensitivity, 3x10^-7 index difference can be detected

0 10 20 30 40 50

0 100 200 300 400 500

Intensity (uW)

Thickness of water (nm)

1.330 1.331 1.332 1.333 1.334 1.335 1.336 0

50 100 150 200 250 300 350

Intensity (uW)

Refractive index of water

Sensitivity

Dielectric/metal Hybrid MZI

1000 mμ

In Out

1000 mμ 1000 mμ 1000 mμ 2000 mμ 1000 mμ 1000 mμ 1000 mμ

Coupling Loss : Fiber-Dielectric WG : ~ 1.26 dB

Insertion Loss : Y-junction : ~ 0.5dB

Coupling Loss : Dielectric WG-Metal WG : ~0.6dB

Propagation Loss of Metal WG : ~ 8.5dB/mm Propagation Loss of Dielectric WG : ~ 0.02dB/mm

10 m5 mμμ

5 mμ

s 1.45 n=

core 1.49 n = 3 mμ

0.4 mμ 50nm

3 mμ

50nm 15nm

1.333 ncl=

em 1.49 n =

s 1.45 n =

h a

λ=780 nm: 5mW

Total Loss : ~ 15 dB

Loss Layer structures

Y-Branch : ~ 3dB

dielectric metal dielectric

Comparison of sensors

Dielectric Au

Sensing Au Surface Sensing layer

Added function

size Optical

loss Sensitivity

Polarizati on Archi- tecture

In situ heating -

Electrical signal transmission -

Integrated Optics (Smaller amount of analyte,

Easy to make array) Integrated Optics

(Smaller amount of analyte, Easy to make array) Bulk optics

(Larger amount of analyte Difficult to make array)

Lowest (MZI) Lower

(MZI possible) High

(ATR required)

Higher Higher

High

TE and TM TM

TM

Dielectric Waveguide MZI LRSP Waveguide MZI

SPR in ATR

angle/wavelength scan in ATR

Metal on high index prism

Metal on membrane waveguide

Dielectric waveguide Phase difference detection in MZI Phase difference detection in MZI

Summary of SP

Summary of SP - - waveguide Sensors waveguide Sensors

z High Sensitivity

- Ability to detect small molecules (e.g. a water monolayer in water) - Determination of concentration, specificity, kinetic parameters

z Label free

z Requires less amount of analyte z Compact size

z Broadly applicable platform

- receptor provide specificity to target analytes - waterly (bio), gas, chemical concentration z Novel technology

z Easy to make array format

z Micro-fluidic flow cell can be integrated

z Potential one chip integration of MZI/LD/PD

Ekmel Ozbay, Science, vol.311, pp.189-193 (13 Jan. 2006).

Some of the challenges that face plasmonics research in the coming years are

(i) demonstrate optical frequency subwavelength metallic wired circuits

with a propagation loss that is comparable to conventional optical waveguides;

(ii) develop highly efficient plasmonic organic and inorganic LEDs with tunable radiation properties;

(iii) achieve active control of plasmonic signals by implementing electro-optic, all-optical, and piezoelectric modulation and gain mechanisms to plasmonic structures;

(iv) demonstrate 2D plasmonic optical components, including lenses and grating couplers, that can couple single mode fiber directly to plasmonic circuits;

(v) develop deep subwavelength plasmonic nanolithography over large surfaces;

(vi) develop highly sensitive plasmonic sensors that can couple to conventional waveguides;

(vii) demonstrate quantum information processing by mesoscopic plasmonics.

Nano-plasmonics