Surface-Plasmon Sensors

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1 Surface-Plasmon Sensors Seok Ho Song Physics Department in Hanyang University Dongho Shin, Jaewoong Yun, Kihyong Choi Gwansu Lee, Samsung Electro-Mechanics

2 Contents Dispersion relation of surface plasmons Sensors based on surface plasmon resonance (SPR) Localized surface plasmon resonance (LSPR) sensors Surface-plasmon-polaritons waveguide sensors

3 Surface plasmons at dielectric-metal boundaries

4 Dispersion relation of surface plasmons ) ( ω ω ω ε p m = m d x m d k c ε ε ω 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 ) (1 ) ( p d d p sp x c k k ω ω ε ε ω ω ω + = =

Surface plasmon dispersion relation: k x ω ε mε d = c ε m + ε d 1/ 2 k zi 2 ω ε i = c εm + εd 1/2 ω ω = ω + ck 2 2 2 2 p x ck x ε d Radiative modes (ε' m > 0) real k x real k z

5 Surface plasmon dispersion relation: k x ω ε mε d = c ε m + ε d 1/ 2 k zi 2 ω ε i = c εm + εd 1/2 ω ω = ω + ck p x ck x ε d Radiative modes (ε' m > 0) real k x real k z ω p ω p Quasi-bound modes ( ε d < ε' m < 0) imaginary k x real k z 1+ ε d z Dielectric: ε d x Metal: ε m = ε ' m + ε " m Bound modes (ε' m < ε d ) real k x imaginary k z Re k x

6 Plasma resonance in summary

7 Excitation of surface plasmons

9 Brewster condition?

10 BREWSTER S ANGLE = 0 ; when θ 1 + θ 2 = 90 o Brewster angle only for TM pol. Figure 2.5 Reflection and transmission coefficients as a function of incident angle for air to glass interface. (Note) Brewster s condition is a consequence of impedance matching with reference to the vertical direction x No reflection For TM : θ 1 + θ 2 = 90 o From Snell s law : n1 sinθ 1 = n2 sinθ2 η2 sinθ1 = η1 sinθ2 η 1x = η2x : Brewster s condition

11 Does Does the the condition condition of of the the surface surface plasmon plasmon resonance resonance match match the the Brewster s Brewster s condition? condition? θ sp = θ Brewster!!! Brewster s condition Matching of characteristic wave impedance at normal direction Snell s law: η 1x = η2x n sinθ = n sin θ, n sinθ = n sinθ n n sinθ = sinθ = cosθ n3 n3 n2 2 n 2 n 3 = 1 sin θ1 = 1 sinθ3 n3 n3 n1 nn sinθ3 2 2 n1 + n2 n = ( nk ) ( nk ) θ 1 + θ 2 = 90 o ε sinθ3 = = 2 2 c n1 + n2 c ε1+ ε 2 sinθ k ω sp when θ 1 + θ 2 = 90 o Let s consider the light propagation in reciprocal direction nn ω 2 ε ε E ε 1 θ 1 ε 3 k sp metal θ 2 θ3 E = 0 ω ε1ε 2 = c ε + ε 1 2

12 Sensors based on surface plasmon resonance (SPR)

13 Surface plasmon resonance (SPR) sensor

15 Concept of SPR Biosensing ω εmεd β = = Re{ β} + Im{ β} c ε + ε M D Re{ β} k n k: free-space wavenumber

16 Concept of SPR Biosensing 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 o

18 SPR imaging 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

19 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

20 Localized surface plasmon resonance (LSPR) (from propagating to localized plasmons)

A novel ultrahigh-resolution surface plasmon resonance biosensor with an Au nanocluster-embedded dielectric film The detection performance of conventional surface plasmon resonance (SPR) biosensors

22 A novel ultrahigh-resolution surface plasmon resonance biosensor with an Au nanocluster-embedded dielectric film The detection performance of conventional surface plasmon resonance (SPR) biosensors is limited to a 1 pg/mm 2 surface coverage of biomolecules. Au nanocluster-enhanced SPR biosensor provides the potential to achieve an ultrahigh-resolution detection performance of approximately 0.1 pg/mm 2 surface coverage of biomolecules. GAS Au nanoclusters 4 nm size 6 nm interval DNA Biosensors and Bioelectronics 19 (2004)

23 Localized surface plasmon resonance (LSPR)

24 Sensing using Nanoshells

26 Waveguide sensors based on long-range surface plasmon polaritons (LR-SPPs)

27 Metal strips guiding surface plasmon polaritons thickness ~ 10 nm metal strip dielectric

28 surface plasmon-polaritons Long-Range SPP: weak surface confinement, low loss frequency Short-Range SPP: strong surface confinement, high loss in-plane wavevector

29 LR-SPP and SR-SPP on thin metal films Coupling of Surface Plasmon Polaritons

30 Dispersion curves of a metal slab 2.0 Real part of Effective index Imaginary part of Effective index a b 10 0 a b 1.9 s b 10-1 s b β r /k β i /k x x thickness (h : nm) Symmetric Mode Field Profile a b s b thickness (h : nm) H y (a.u.) 0.0 Anti-Symmetric Mode length (μm)

31 Field profile of slab SPP modes) Symmetric Mode H y (a.u.) H y (a.u.) h=20nm h=40nm h=100nm h=200nm h=20nm 0.2 h=40nm h=100nm h=200nm length (μm) Field enhancement at the boundary length (μm) Sensitive to environment Anti-Symmetric Mode h=20nm h=40nm h=100nm h=200nm H y (a.u.) H y (a.u.) h=20nm h=40nm h=100nm h=200nm length (μm) length (μm)

Dispersion curves of a finite-width strip Metal Thickness Metal Stripe width 1.64 1.62 1.60 aa b o ss b 0 1.575 1.

500 0 50 100 150 200 thickness of metal(nm) 0 5 10 15 20 25 30 metal stipe width(μm) 1.4x10-2 10-2 10-3 1.

32 Dispersion curves of a finite-width strip Metal Thickness Metal Stripe width aa b o ss b β r /k β r /k slab(20nm) aa b o ss b thickness of metal(nm) metal stipe width(μm) 1.4x x10-2 β i /k 0 1x10-4 1x10-5 aa b o ss b 0 β i /k 0 slab(20nm) x10-5 aa b o ss b thickness of metal(nm) metal stipe width(μm)

33 LR-SPP waveguides Long-Range Long-Range Surface Surface Plasmon Plasmon Polaritons Polaritons Waveguide Waveguide LR-SPPs W/G Structure SiO2 Au ~ 20nm LR-SPPs Waveguide Devices Optical modulator & switch Optical add/drop filter Sergey I. Bozhevolnyi Group (Denmark) ~ 5um Mode profile of SS 0 b mode Vertical directional coupler Seok Ho Song Group (Korea) Bragg grating filter Pierre Berini Group (Canada) optical Sensor? Best measurements: - Attenuation: 3.2 db/cm - Coupling to SMF: < 0.2 db

LR-SPP Waveguide Sensor Long-Range Long-Range Surface Surface Plasmon Plasmon Polaritons Polaritons Waveguide Waveguide Sensor Sensor 350 Output signal 300 Intensity (uw) 250 200 150 100 50 Metal

34 LR-SPP Waveguide Sensor Long-Range Long-Range Surface Surface Plasmon Plasmon Polaritons Polaritons Waveguide Waveguide Sensor Sensor 350 Output signal 300 Intensity (uw) Metal waveguide Reference arm Sensing arm Refractive index of water If something is changed Mode of LR-SPP & output signal is changed Metal waveguide sensor - Air or water background - Polarizing waveguide - Higher waveguide sensitivity - Higher waveguide loss : Hybrid waveguide structure - Added functionality : In situ heating or electric field Dielectric waveguide sensor - Air or water background - Non polarizing waveguide - Low waveguide sensitivity - Lower waveguide loss - No added functionality

35 LR-SPP Waveguide Sensor Region 1 Region 2 If something is changed Mode of LR-SPP is changed The output signal (Interferometer signal) is changed Region 1 Cross Section ε em, d em ε Au, d Au nclad ~1.47( dielectric) Metal waveguide Reference arm Sensing arm Region 2 Cross Section ε em, d em ε Au, d Au Liquids (ex. Bio-molecules) nsens ~1.33( water)

36 LR-SPP Waveguide on a membrane Region 2 (sensing region) λ = 1.55μm ε = ε, d = 20 nm, w= 5μm m Au Au ε = 1.33, ε = 1.45 c 2 2 em N eff thickness of membrane (nm) Propagation loss (db/mm)

37 Sensitivity of LR-SPP Waveguide Sensor ε ε, d Au Au, d em em (varialbe) ε c Index change by thermal/density Index change by thichness ε ε Au em ε c,, d Au d em ε, d (variable) a a Almost 1 n eff n c = d em =50nm n d eff a d em =50nm = / nm N sens N sens index(n c ) thickness of d a (nm)

38 Sensitivity of LR-SPP sensor : an embedded structure ε, ε, d (variable) a a Au ε, em d Au dem ε, em dem ε, d (variable) a a ε, d Au Au ε c ε c Effective Index, N eff n d eff a = / d em =100nm nm Effective Index, N sens n eff d a d em =100nm = / nm Thickness of d a [nm] Thickness of d a [nm]

39 Sensitivity of LR-SPP sensor : embedded thickness Increase in embedded layer thickness Reduction of mode size Increase in E-Field Stronger interaction Better sensitivity

Cross section Metal 5μm Receptor dielectric SiO2 20nm SiO2 100nm

40 Intensity modulation from an interferometer 1000μm 2 In 1 Out 40μm 1000μm 500μm 500μm 2000μm 500μm 500μm 1000μm 1 Cross section 2 Cross section Metal 5μm Receptor dielectric SiO2 20nm SiO2 100nm dielectric SiO2(1.47) metal Air(1.0) water substrate membrane 1 membrane 2

41 Sensitivity Intensity (uw) Intensity (uw) Thickness of water (nm) Refractive index of water 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

6dB Insertion Loss : Y-junction : ~ 0.5dB Y-Branch : ~ 3dB Propagation Loss of Metal WG : ~ 8.5dB/mm 50nm n = 1.45 s 3μm n = 1.

42 Dielectric/metal Hybrid MZI λ=780 nm: 5mW In dielectric metal 1000μm dielectric Out 1000μm 1000μm 1000μm 2000μm 1000μm 1000μm 1000μm Loss Layer structures Coupling Loss : Fiber-Dielectric WG : ~ 1.26 db Coupling Loss : Dielectric WG-Metal WG : ~0.6dB Insertion Loss : Y-junction : ~ 0.5dB Y-Branch : ~ 3dB Propagation Loss of Metal WG : ~ 8.5dB/mm 50nm n = 1.45 s 3μm n = 1.49 core 0.4μm n = 1.45 s 15nm n = 1.49 em n = cl 3μm a h 50nm Propagation Loss of Dielectric WG : ~ 0.02dB/mm Total Loss : ~ 15 db 5μm 10μm 5μm

Comparison of sensors SPR in ATR LRSP Waveguide MZI Dielectric

difference detection in MZI Phase difference detection in MZI Sensing

waveguide Polarizati on TM TM TE and TM Sensitivity High Higher Higher

size Bulk optics (Larger amount of analyte Difficult to make array)

Sensing Surface Au Au Dielectric Added function - In situ heating

43 Comparison of sensors SPR in ATR LRSP Waveguide MZI Dielectric Waveguide MZI Architecture angle/wavelength scan in ATR Phase difference detection in MZI Phase difference detection in MZI Sensing layer Metal on high index prism Metal on membrane waveguide Dielectric waveguide Polarizati on TM TM TE and TM Sensitivity High Higher Higher Optical loss High (ATR required) Lower (MZI possible) Lowest (MZI) size Bulk optics (Larger amount of analyte Difficult to make array) Integrated Optics (Smaller amount of analyte, Easy to make array) Integrated Optics (Smaller amount of analyte, Easy to make array) Sensing Surface Au Au Dielectric Added function - In situ heating Electrical signal transmission -

44 Summary of SP-waveguide Sensors Novel technology High Sensitivity - Ability to detect small molecules (e.g. a water monolayer in water) - Determination of concentration, specificity, kinetic parameters Label free Compact size Requires less amount of analyte Broadly applicable platform - receptor provide specificity to target analytes - waterly (bio), gas, chemical concentration Easy to make array format Micro-fluidic flow cell can be integrated Potential one chip integration of MZI/LD/PD

45 Nano-plasmonics Ekmel Ozbay, Science, vol.311, pp (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.

Surface plasmon waveguides

Surface plasmon waveguides Introduction Size Mismatch between Scaled CMOS Electronics and Planar Photonics Photonic integrated system with subwavelength scale components CMOS transistor: Medium-sized molecule