plasmons surface plasmon resonance plasmonic effects and...

Plasmons

Surface Plasmon Resonance

Plasmonic Effects and Applications

Introduction

• During the last two decades many researches devoted to develop optical sensors for the measurement of chemical and biological quantities. In the beginning, the optical chemical sensors were based on the measurement of changes in absorption spectrum and were developed for the measurement of CO2 and O2

concentrations. Since then, a large variety of optical methods have been used in chemical and biosensors, among them, Surface Plasmon Resonance. In these sensors, a desired quantity is determined by measuring the refractive index, absorbance and fluorescence properties of analyte molecules.

Introduction

• Plasmon: The quanta of waves produced by collective effects of large numbers of electrons in matter when the electrons are disturbed from equilibrium.

• The quantum of Plasma Oscillation is called Plasmon

• Metals provide the best evidence of plasmons, because they have a high density of electrons free to move.

• The name plasmon derives from the physical plasma as a state of matter in which the atoms are ionized. At the lowest densities this means an ionized gas, or classical plasma; but densities are much higher in a metal, the atoms of a solid metal being in the form of ions. In both types of physical plasma, the frequency of plasma-wave oscillation is determined by the electronic density. In a quantum plasma the energy of the plasmon is its frequency multiplied by Planck's constant, a basic relationship of quantum mechanics.

Introduction

• Plasmons play a large role in the optical properties of metals. Light of frequency below the plasma frequency is reflected, because the electrons in the metal screen the electric field of the light. Light of frequency above the plasma frequency is transmitted, because the electrons cannot respond fast enough to screen it. In most metals, the plasma frequency is in the ultraviolet, making them shiny (reflective) in the visible range. On the other hand, some metals, such as copper, have a plasmon frequency in the visible range, yielding their distinct color.

• The geometry of the metal film plays an important role in plasmon frequency. For example gold, has plasmon frequency in the deep ultraviolet, but geometric factors bring it close to the visible.

• In doped semiconductors, the plasma frequency is usually in the infrared.

5

Introduction

• High interest of artists regarding scattering absorption of light from noble metal nanoparticles – source of colors in stained glass windows even before scientifically investigated.

• Sizes, shapes, and compositions of metal nanoparticles can be systematically varied to produce materials with distinct light-scattering properties.

Introduction

• The plasmon energy for most metals corresponds to that of an ultraviolet photon. However, as mentioned above for some metals like silver, gold, the alkali metals, and a few other materials, the plasmon energy can be sufficiently low to correspond to that of a visible or near-ultraviolet photon. This means there is a possibility of exciting plasmons by light.

• If plasmons are confined upon a surface, optical effects can be easily observed. In this case, the quanta are called surface plasmons, SP, and they have the bulk plasmon energy as an upper energy limit.

• Surface plasmons were first proposed to explain energy losses by electrons reflected from metal surfaces. Since then, numerous experiments have involved coupling photons to surface plasmons. Potential applications extend to new light sources, solar cells, holography, Raman spectroscopy, microscopy, and sensors.

Introduction

• Surface plasmons are those plasmons that are confined to surfaces and that interact strongly with light resulting in a polariton, SPP. They occur at the interface of a material with a positive dielectric constant with that of a negative dielectric constant (usually a metal or doped dielectric).

Introduction

Surface plasmons on a plane surface are non-radiative electromagnetic modes, that is, SPP cannot be generated directly by light nor can they decay spontaneously into photons. The origin of the non-radiative nature of SPP is that the interaction between light and SP cannot simultaneously satisfy energy and momentum conservation. This restriction can be circumvented by relaxing the momentum conservation requirement by roughening or corrugating the metal surface. Other method is to increase the effective wave vector (and hence momentum) of the light by some means (discussed later).


• The excitation of surface plasmons by light is denoted as a surface plasmon resonance (SPR) for planar surfaces or localized surface plasmon resonance(LSPR) for nanometer-sized metallic structures.

• Surface plasmon polaritons (SPP), ( coupling between photon and an excitation of a material) are surface electromagnetic waves that propagate parallel along a metal/dielectric interface. For surface plasmons to exist, the complex dielectric constants of the two media must be of opposite sign. This condition is met in the IR-visible wavelength region for air/metal and water/metal interfaces (where the real dielectric constant of a metal is negative and that of air or water is positive). Typical metals that support surface plasmons are silver and gold, but metals such as copper, titanium, or chromium can also support surface plasmon generation.

Surface Plasmon and Localized Surface Plasmon

Resonance

• Surface Plasmon (SP): Charge density wave that exists at the interface between metal and dielectric -Plasmons propagate along metal dielectric interface

• Excitation of SP: momentum of incident photon = that of plasmon →resonance

• Sensing; measurement of absorption: function of angle of incidence or function λ (we used the latter)

• Light at certain λ causes conduction electrons oscillate around the nanoparticles

• LSPR is similar to SPR but it is localized – refers to the frequency at which plasmons oscillate around the nanoparticle – or when light is in resonance with collective oscillation of electrons

• Sensing; measurement of absorption: function of angle of incidence or function λ (we used the latter)

Derivation of dispersion relation of Surface Plasmon Polaritons

Dielectric

Metal

)(exp)0,,0( tzkxkiHH zdxdydd

)(exp),0,( tzkxkiEEE zdxdzdxdd

)(exp)0,,0( tzkxkiHH zmxmymm

)(exp),0,( tzkxkiEEE zmxmzmxmm Z>0 Z<0

Maxwell’s equation in the medium i ( i = metal or dielectric )

t

EH i

i

t

HE i

0 0 Ei 0 H

At the boundaries

dxmx EE ,, zddzmm EE dymy HH ,,

t

EH i

ii

Start with curl equation for H in the medium i

)(exp)0,,0( tzkxkiHH zixiyii

)(exp),0,( tzkxkiEEE zixizixii

),0,(),0,(,, ziixiiyixiyizixiyizixiyizi EiEiHikHikx

H

x

H

x

H

z

H

z

H

y

H

xiiyizi EHk xmmymzm EHk

xddydzd EHk

dxmx EE ,,

yd

d

zdym

m

zm Hk

Hk

xm xdH Hd

zd

m

zm kk

Continuity of E|| And H|| across the boundary

Existence condition for SPPs

d

zd

m

zm kk

Existence condition for SPPs

Dispersion Relation

xdxm kk Relation for kx ( continuity of E|| and H|| )

True at any boundary

For any EM wave

2

22

ckk izix

Both for metals and dielectrics 2

2

ziixsp kc

kk

d

zd

m

zm kk

2/1

dm

dmxc

k


n2

i

n1 > n

2

i

Incident

light

t

Transmitted

(refract ed) light

Reflected

light

kt

i>

c

c

TIR

c

Evanescent wave

ki

kr

(a) (b) (c)

Light wave travelling in a more dense medium strikes a less dense medium. Depending onthe incidence angle with respect to c, which is determined by the ratio of the refractive

indices , the wave may be transmitted (refracted) or reflected. (a) i < c (b) i = c (c) i

> c and total internal reflection (TIR).

© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

SPP

• Condition for possible SPP: The frequency-dependent permittivity of the metal, εm and the dielectric material, εd , must have opposite signs. This condition is satisfied for metals.

• For example, the SP wavevector for a silver–air interface in the red part of the visible spectrum is found to be 1.03k0. This increase in momentum is associated with the binding of the SP to the surface, and the resulting momentum mismatch between light and SPP of the same frequency must be bridged if light is to be used to generate SPP.

SPP

• Another characteristic of the interaction between

the surface charges and the electromagnetic

field is that, the field perpendicular to the surface

decays exponentially with distance from the

surface and SPP propagate along the surface, .

The field is called evanescence or near field and

is due to the bound, non-radiative nature of SPP,

which prevents power from propagating away

from the surface.


2/1

dm

dmsp

ck

Techniques to Induce Surface Plasmon Resonance

• Several configurations of SPR devices exist, and serve as sensors. These optical devices are capable of exciting the SPWs and are also used to interrogate the SPR. The configurations that are known and used today are the following:

• Surface plasmon resonance sensors using optical prism couplers

• Surface plasmon resonance sensors using grating couplers

• Surface plasmon resonance sensors using optical waveguides

• Surface plasmon resonance sensors based on optical fibers

• Scattering from a defect on a surface, such as a hole with subwavelength scales (generates LSP).

• A periodic nanostructures in the metal surface.


n2

i

n1 > n

2

i

Incident

light

t

Transmitted

(refract ed) light

Reflected

light

kt

i>

c

c

TIR

c

Evanescent wave

ki

kr

(a) (b) (c)

Light wave travelling in a more dense medium strikes a less dense medium. Depending onthe incidence angle with respect to c, which is determined by the ratio of the refractive

indices , the wave may be transmitted (refracted) or reflected. (a) i < c (b) i = c (c) i

> c and total internal reflection (TIR).


E

By

Bz

z

y

O

B

E// Ey

Ez

(b) TM mode(a) TE mode

B//

x (into paper)

Possible modes can be classified in terms of (a) transelectric field (TE)and (b) transmagnetic field (TM). Plane of incidence is the paper.


Note energy matching between SPP

and incident light


• Surface Plasmon resonance (SPR) is a non-destructive analysistechnique, which is used in the investigation of thin layers of molecules upon a material surface. More specifically SPR is capable of detecting changes in the refractive index (n) occurring near the surface of a metal (within ~200nm). It is a physical process, which occurs when plane polarized light hits a metal film under total internal reflection conditions.

• When a light beam, traveling from a dense to a less dense medium, strikes the surface of a prism this causes the light to bend towards the interface plane. As depicted in the figure changing the angle of incidence changes the resulting light until a critical angle is reached. Upon reaching the critical angle all the incoming light is reflected within the prism, this is referred to as total internal reflection (TIR). Light is not generated during TIR, however the electrical field of the photons extends approximately a quarter of the wave length beyond the reflecting surface.


• The prism described above is generally coated with a thin metal film placed in contact with the base of the prism (usually the reflection site), e.g. gold. The use of a metal sensing surface in SPR is critical as this technique capitalizes upon the fact that metals contain electrons, which behave as a continuous “sea” of charge. This "sea" of charge can undergo charge-density oscillations, plasmons, at the surface of the conductor, particularly at a surface in contact with an insulator. Furthermore a molecular layer of interest can be coated onto the thin metal film on the side opposite the prism.


• The metal film used must have conduction band electrons capable of resonating with the incoming light at a suitable wavelength. Metals that satisfy this condition are silver, gold, copper, aluminum, sodium and indium. In addition, the metal on the sensor surface must be free of oxides, sulfides and should not react to other molecules on exposure to the atmosphere or liquid. The thickness of the metal layer is also of great importance. Above an optimum thickness the dip in reflective light becomes shallow, and below an optimum thickness the dip becomes broader; thus affecting the SPR angle.


• When a particular type of light (from the light source) strikes the metal sensor, surface plasmon waves (SPW) are generated at the interface between the conductive metal and the insulating molecular layer. In addition to the generation of the SPWs, light is also reflected off of the metal surface. As indicated earlier at TIR, all the energy from the incident light wave will be transferred to the reflected light wave. However, at a particular angle, past the point of TIR, which results in the SPR angle, a majority of the incidence light energy will interact with the generated SPW’s. This results in a phenomenon called resonance. At resonance, the reflected light intensity will be minimal; this intensity corresponds with the SPR angle (the intensity of the reflected light may be measured using the photo-detector.


• The SPR angle is dependent upon several factors, including: properties of the metal film, the wavelength of the incident light and the refractive index of the media on either side of the metal film i.e. molecular layer in contact with the metal sensing surface; (the refractive index is sensitive to temperature, therefore it is important to perform the measurements at defined temperatures as well).


Wavelength vs Reflectance

Surface plasmon resonance sensors using optical prism couplers

– A very suitable geometry for sensors using

attenuated total reflection (ATR) is the

Kretschmann Prism. The Kretschmann

prism is used to measure reactions on a

sensor chip attached to a prism. The

apparatus consists of a sensor chip, a light

source, a light detector, and a prism also

referred to as the Kretschmann Prism.


• In order to promote evanescent waves, rather than coating the prism with a material with a high index of refraction, a sensor chip is attached to the prism with a thin layer of metal. In this scenario, waves are present in the “sea of free electrons” in the metal. when the plasmons have similar properties to that of the evanescent wave, the two couple resulting in SPR. SPR uses energy, therefore the intensity of the light which reflects back from the surface is less than that of the incident on the surface. This intensity may be measured in order to determine the occurrence of SPR.

• Furthermore when a sensor chip is fabricated such that it is capable of changing the nature of its surface plasmon in the presence of an analyte, the presence or concentration of this analyte may be determined.


• Most sensors are operated in the following manner:– “Monochromatic light is directed through the prism

through a range of angles which all cause total internal reflection.

– The sensor chip is coated with receptors to a specific analyte. The concentration of the analyte present on the opposite surface of the sensor chip modifies the resonant frequency of the Surface Plasmon.

– The intensity of the reflected light vs. incident angle will have a minimum that corresponds to the resonant frequency. From the location and magnitude of this minimum the concentration of the analyte can be determined.”

Surface plasmon resonance sensors using optical grating

• In this technique, (see the picture in the next page) the incident electromagnetic radiation is directed towards a medium whose surface has a spatial periodicity (D) similar to the wavelength of the radiation, for example a reflection diffraction grating. The incident beam (red line) is diffracted producing propagating modes which travel away from the interface (blue lines) and evanescent modes which exist only at the interface. The evanescent modes have wavevectors parallel to the interface similar to the incident radiation but with integer 'quanta' of the grating wavevector added or subtracted from it. These modes couple to Surface Plasmons (green line), which run along the interface between the grating and the ambient medium.

Surface plasmon resonance sensors using optical grating

Optical waveguide SPR coupling

mGkk sp ||

Grating coupling geometry

Periodic dielectric constant couples waves for which the K-vectors

differ by reciprocal lattice vector G

Strong coupling occurs when

sin||c

kk de

PG /2

2-D periodic grating structure

Transmission

sp

spk

Kspp

ck

mG

Kair

max2 2

( , ) m d

m d

Pi j

i j

min2 2

( , )d

i j Pi j

Contributed by WA modes Contributed by SPP modes

SPP Model

|| x yG Gspk k i j || x yG Gdiffk k i j

Light illuminated on the surfce of a 2-D periodic perforated film.

Coupling matching equations:

This is an approximated model

Surface plasmon resonance sensors using optical waveguides

– The use of optical waveguides in SPR sensors provides numerous attractive features such as a simple way to control the optical path in the sensor system to suppress the effect of stray light. The process of exciting an SPW in this configuration is similar to that of the Kretschmann ATR coupler. A light wave is guided by the waveguide and, entering the region with a thin metal layer, it evanescently penetrates through the metal layer. If the SPW and the guided mode are phase matched, the light wave excites an SPW at the outer interface of the metal. Theoretically, the sensitivity of waveguide-based SPR devices is approximately the same as that of the corresponding ATR configurations.

Light

n2

A planar dielectric waveguide has a central rectangular region ofhigher refractive index n1 than the surrounding region which hasa refractive index n2. It is assumed that the waveguide isinfinitely wide and the central region is of thickness 2 a. It isilluminated at one end by a monochromatic light source.

n2

n1 > n2

Light

LightLight


n

y

n2 n

1

Cladding

Core z

y

r

Fiber axis

The step index optical fiber. The central region, the core, has greater refractiveindex than the outer region, the cladding. The fiber has cylindrical symmetry. Weuse the coordinates r, , z to represent any point in the fiber. Cladding isnormally much thicker than shown.


y

E(y)m = 0 m = 1 m = 2

Cladding

Cladding

Core 2an

1

n2

n2

The electric field patterns of the first three modes (m = 0, 1, 2)traveling wave along the guide. Notice different extents of fieldpenetration into the cladding.


Fiber axis

12

34

5

Skew ray1

3

2

4

5

Fiber axis

1

2

3

Meridional ray

1, 3

2

(a) A meridionalray alwayscrosses the fiberaxis.

(b) A skew raydoes not haveto cross thefiber axis. Itzigzags aroundthe fiber axis.

Illustration of the difference between a meridional ray and a skew ray.Numbers represent reflections of the ray.

Along the fiber

Ray path projectedon to a plane normalto fiber axis

Ray path along the fiber


Low order modeHigh order mode

Cladding

Core

Ligh t pulse

t0 t

Spread,

Broadened

light pulse

IntensityIntensity

Axial

Schematic illustration of light propagation in a slab dielectric waveguide. Light pulseentering the waveguide breaks up into various modes whic h then propagate at differentgroup velocities down the guide. At the end of the guide, the modes combine toconstitute the output light pulse which is broader than the input light pulse.

© 1999 S.O. Kasap , Optoelectronics (Prentice Hall)

Surface plasmon resonance sensors based on optical fibers

• Optical fiber SPR probes present the highest level of miniaturization of SPR devices, allowing for chemical and biological sensing in inaccessible locations. The ability to transmit optical signals over a long distance makes the use of optical fibers very attractive. Fiber optic waveguides have a number of advantages over prism-based sensors. They are inexpensive and can easily be used to make disposable sensors for medical tasks. Fibers are also very small and have no moving parts, giving them a much broader range than the Kretschmann sensors and making multiple sensorarrays a possibility.


• A fiber optic SPR sensor is built using a large diameter (~400 micron) and multimode fiber. Cladding is removed from a portion of the fiber, and a surface plasmon metal layer e.g. silver is deposited instead. The length from which the cladding is removed is dependant upon the diameter of the fiber, and determines the number of reflections occurring at the surface plasmon metal interface. If the length is too short, not enough coupling will occur. If the length is too long, coupling will be very strong and the minimum coupling intensity will be difficult to determine.


• When light enters a fiber at a specific angle, corresponding to a specific mode, it will propagate through a multimode optical fiber. Although modes are more of an energy distribution, in the fiber, they can also be thought of as angles of total internal reflection as the light bounces back and forth along the fiber. Light which enters the fiber at larger angles (i.e. low-order modes) bounces back and forth at a slow pace, whereas light which enter the fiber at a tighter angles (i.e. higher-order modes) bounces back and forth a fast pace. At low-order modes the energy is distributed in the fiber core, whereas the energy for high-order modes spreads into the cladding, and beyond the waveguide.


• In order to achieve SPR sensing, as opposed to sweeping through a range of coupling angles in the Kretschmann Prism, the fiber only sweeps through a number of coupling wavelengths. The wavelengths are interrogated, i.e. measuring the amount of each wavelength leaving the fiber, using a broadband, multi-wavelength source e.g. white light. Using a spectrophotometer it is then possible to determine which wavelength coupled with the surface plasmon and how much analyte (species being analyzed) is present.

Single Hole

Holes & Periodic nanostructures in the metal surface

Enhanced Optical Transmission

T/f ~(d/)2

Beth theory Ebbesen

observation

T = Transmission

f= Fraction of area

Enhanced transmission through nano

apertures

Enhanced transmission through nano

apertures

1. Nano apertures in plane metal surface

2. Periodic holes convert photons in SPPs

3. SPPs reemit photons behind metal

Ebbesen et al Extraordinary optical transmission through sub-wavelength hole arrays. Nature 391, 667–669 (1998).

Ebbesen et al. Nature 1998, 391,667

• 200 nm thick Ag

• 150 nm holes

• 900 nm spacing

• Transmission efficiency =

fraction of light transmitted/

fraction of surface holes area

= 2.

• More than twice the light

that impinges on the holes is

transmitted through the film!

Ebbesen et al. Nature 1998, 391,667

• Hole spacing determines peak position

•Peak position independent of hole d

• Independent of metal (Ag, Cr, Au)

• Must be metal (Ge doesn’t work)

Single hole in metallic surface

Ahmadreza Hajiaboli, Mojtaba Kahrizi and Vo-Van Truong

J. Physics D: Applied Physics

Applications

• The SPR signal is directly dependent on the change of the refractive index of the medium on the sensor side of the SPR surface.

• The spectra will be generated for a metal surface once with and once without a coated molecular layer. Then, the shift in SPR angle between the two can be quantified and used to calculate the thickness or refractive index of the adhered molecules. SPR has proven useful in determining both growth in the thickness of a molecular layer and loss in thickness, even of a single monolayer.

• Along with its ability to determine the thickness of coated films, SPR has also emerged as a technology in the area of sensors (e.g., for the detection of physical quantities, chemicals and biological purposes). Physical quantities (such as temperature and humidity) can be deduced from changes in refractive index.

Applications

• Surface plasmons (SP) are of interest to many scientists, ranging from physicists, chemists, biologists and engineers. Advanced technologies allow metals to be structured and characterized on the nanometer scale to enabled us to control SPP properties for specific applications. For example, SPP is being explored for their potential in optics, magneto-optic data storage, microscopy and solar cells, as well as being used to construct sensors for detecting biological molecules.

60

Applications

• Provide platform for monitoring molecular interactions

• Detect local refractive index change occurring when target analytebinds to metal film independent of chemical nature - various molecules can be used

• Sensitivity arises from the distance dependence of the electric fields that extend from the nanoparticles’ surface – ld

• SPR sensor sensitivity higher than that of LSPR

• SPR spectroscopy uses conventional ATR Kreschmann config –LSPR uses extinction or transmission measurements – less expensive

Applications

• Chemical sensing can use changes in refractive index to indicate changing concentrations of molecules adhered to the metal surface (as a result of chemical reactions). Biosensing can also use refractive index changes to deduce the occurrence of binding interactions (such as between antigens and antibodies). SPR also provides the important advantage of being able to monitor reactions in real-time, without the need to go through the often complicated process of labeling molecules with fluorescent or radioactive probes.

• Like all surface analysis techniques, SPR has its limitations in terms of sensitivity (the smallest amount of molecule detectable), resolution (the smallest difference in SPR angle distinguishable) and sample characteristics(geometry, thickness, etc.). However, this technique still provides a remarkable variety of capabilities for the characterization of reaction kinetics and thin film properties, with a high degree of sensitivity.

Applications

• Most of the interesting SPP-mediated effects happen when the metal surface at which the SPP is generated is covered with a dielectric thin film. The presence of even very thin films measurably alters the behavior of the SP reflectivity resonance -- typically shifting the incident angle at which resonance occurs and broadening the reflectivity dip. These effects can be used to make devices. For example, if the film is electro-optically active, one can make an optical modulator; chemical changes in the dielectric over layer can be used to make a chemical sensor.

Applications

• There are many areas of applications of SPR sensors. For instance they are used for measurements of physical quantities, chemical sensing, and biosensing.Because of the complexity of biological systems and the number of possible interference to chemical nanosensors, the need for added specificity in cellular analyses can arise: nanobiosensors are then employed. Biological receptor molecules (i.e., antibodies, enzymes, etc.) are used to provide added specificity. The different types of bioreceptor molecules that have been used for the fabrication of nanobiosensors include antibodies, oligonucleotides, and enzymes, thereby allowing for the detection of a wide array of analytes.

Applications in Technology

• Plasmons have been considered as a means of transmitting information on computer chips, since plasmons can support much higher frequencies (into the 100 THz range, while conventional wires can not tolerate even tens of GHz.

• They have also been proposed as a means of high resolution lithography and microscopy due to their extremely small wavelengths. Both of these applications have seen successful demonstrations in laboratory environment.


• It is evident that deeply sub-wavelength focal spots cannot be formed through conventional focusing using a lens system or microscope objective. This is due, primarily, to the lack of high-index media at visible frequencies. What if, however, one was able to achieve a high effective index with conventional optical materials? That is the potential of surface plasmon optics. By employing geometries of conductors (such as metals or doped semiconductors) with dielectrics (such as air or glass), modes at optical frequencies can be created with effective indices of refraction that are orders of magnitude higher than those of the constituent materials. In fact, these indices can be so high as to create X-ray wavelengths (less than 10nm) with visible frequencies.

• The reason surface plasmon modes can achieve anomalously high wave-vectors at visible frequencies is because they are mediated by electrons rather than free space optical fields.

High Index of refraction

Super Lenses??

38

39

19

/103)10(

106.12mJ

m

JeVityEnergyDens

34 /2.0/ mJcTityEnergyDens

Energy of 2eV stored in a volume of 1nm3

Energy density of our solar system


• The ability to focus the optical field to deeply sub-wavelength dimensions opens the door to an entirely new class of photonic devices. If one could combine the imaging powers of X-ray wavelengths with the economy and maturity of visible light sources, one could greatly broaden the practical engineering toolbox. Imagine focusing visible photons to spatial dimensions less than ten nanometers. By doing so, electron beam microscopy is immediately displaced by optical microscopy, replacing expensive electron beam sources with inexpensive visible lasers. Beyond simple economics, though, this achievement would allow for the nanoscale imaging of living biological samples.

•


• Combining Plasmonics Effects and Photonic Crystals

• Photonic band structure refers to the modification of the propagation properties of electromagnetic waves traveling through a periodically modulated dielectric. The effects of scattering and interference of the light by the periodic structure would result in a change in the propagation of the waves. The alteration in the propagation properties is particularly significant when the wavelength of the light is approximately equal to the spacing between the dielectric structures. In this regime photonic band gaps--frequency intervals in which no photon modes are allowed--can be created for appropriately designed dielectric arrays. The ability to create volumes of space in which no photons of a given band of energies can exist has a number of fundamental and applied consequences.

Application in Health Science

• Surface plasmon resonance is used by biochemists to detect the presence of a molecule on a surface.

• SPR reflectivity measurements can be used to detect DNA or proteins by the changes in the local index of refraction upon adsorption of the target molecule to the metal surface. If the surface is patterned with different biopolymers, the technique is denoted as Surface Plasmon Resonance Imaging (SPRI).

• For nanoparticles, localized surface plasmon oscillations can give rise to the intense colors of solutions of plasmon resonance nanoparticles and/or very intense scattering. Nanoparticles of noble metals exhibit strong ultraviolet-Visible absorption bands that are not present in the bulk metal. Shifts in this resonance due to changes in the local index of refraction upon adsorption of biopolymers to the nanoparticles can be used to detect biopolymers such as DNA or proteins.


• Areas of interest in this domain are for instance

the examination of protein-protein or protein-DNA

interactions, in order to detect conformation

changes in an immobilized protein. In addition to

above mentioned, biosensors may also be used

to monitor the glucose levels in diabetic patients.

The system under study would be based upon

direct measurements of the reflection and

transmission spectra in the near infrared

spectrum.


– Drug discovery

– Traditionally drugs were discovered via tedious efforts, however with the advent of biosensors this process may be sped up. Biosensors offer the possibility of detecting the interaction between a particular target and a possible drug. This is made possible without the use of markers or the detection of color changes of fluorescence, which in turn eliminates any potential cause of interference and furthermore test samples do not need to be purified and can be reused. Biosensors also have the capability of measuring how quickly and how well a potential drug binds to a target.

72

Researches done in our group

• AFM of Au-PS

colloidal crystal (Au

can’t be seen here –

too small)

• Ordered multilayers of

composites 18-20

layers

PS microspheres: 510 nm; Au: 5 nm

Vertical deposition 55oC, 3 days

Aluminium cap

Meniscus

back

Meniscus

front

Surface

dropping

velocity

PS – Au

suspension

topcock

Water

evaporation

x

z

Substrate

Convective

flow

Meniscus region

Attractive capillary forces

Inclination

angle

nanospheres colloidal crystal

(b) (c)

(a)

a) Vd = 100 µm/s

b) Vd = 40 µm/s

c) Vd = 15 µm/s

S. Badilescu, M. Kahrizi, Journal of Materials Science: Materials, 2007

Self-Assembly Techniques

74

Results

• Sample prepared with 200 nm PS

Spheres – not annealed

• Nanohole present – evenly

distributed



• Nanoholes present – some imperfections

Nanoholes fabricated using Porous Silicon Method

Nanocups Nanorings

Potential Applications

Mirror

Nanoholes metallic

structure

Cladding Core

Optical Biosensor

A.R. Hajiaboli & M. Kahrizi,.. CSTC, 2007

79



• Nanorings and nanoholes present

• Aggregation effects around holes

•Size of holes is less than the size of

spheres

An Example to fabricate periodic nanostructures

• Fabricated many samples – PS sphere sizes: 100 nm, 200 nm, 500 nm and 700 nm

• Resulted in hole and ring structures

• Ring structures are not continuous ring structures - made of nanoparticles which do not touch one another

• Some samples were annealed and some were not

• Observed aggregation effects around holes for certain samples

• Observed PS spheres not completely removed in some cases

• Nanohole/nanoring array prepared with 530 nm PS and 20 nm Au – more rings

• Sample annealed at 900C for 20 min

• Inset: enlarged image of a region where PS spheres were not completely removed. - Au nanoparticles are around and on the top of the spheres

81

Sample Preparation

Silanization

Substrate

Si

R

NH2

Silane

Molecule

Amino

Group

Organic

Radical

OH group on substrate will

react with silane molecule

Amino Silane will bond to Au

82

Sample Preparation

Preparation of Colloidal Au by Reduction of

Chloroauric Acid

15-20 mg of chloroauric acid is dissolved

in ~80mL of DI water – solution heated

Solution begins to boil - Au sodium citrate

solution (1%) added to boiled solution

Solution boiled for another 10-15 minutes

- left to cool down to room temperature

Once ready the solution became a

deep red/purple

83

Sample Preparation

Sample Preparation: Self-Assembly

Silanized Substrate

Silanized sample immersed in Au

and PS mixture

Multilayer of Au and PS composite

structure formed by self assembly

Substrate kept in this mixture at 55-600C

For 2-3 days

84

Results

Structure of the Au Nanoparticles

• X-ray diffraction patterns of PS-Au composite

• Trace a and b depict presence of Au, Trace c refers to sample with very low amount of Au

• Trace a weak peaks= less Au, Trace b stronger peak = more Au

• Trace b indicates 6-9 nm particle sizes

Gold Crystalline Structure - fcc

85

Results

Geometrical Characteristics

Sensitivity decreases as spacing

increases between holes

Sensitivity increases for smaller spheres

Density of the holes decreases as sphere sizes increases

Average spacing of the holes increases

linearly with diameter of PS spheres

Average hole diameter increases linearly with diameter of PS spheres

86

Results

UV-VIS Spectrum of a Nanohole/Nanoring Array -

Sensitivity of the Structure (/n)

A) In water and B) 2-PROPANOL (sample annealed for 30 min at

110C)

Au LSPR band red-shifted by 8 nm in 2-propanol S = 340 nm/RIU

87

Sample Preparation

Expression of Protein (AT5G0701.1)

and Production of Antibody• Preparation was done in collaboration with the

Department of Biology at Concordia University

• Adsorption of Antibody on the sensor platform:– Dilution

– Incubation of Polyclonal antibody – 1 hour

– Rinsing of the platform

– Recording of spectrum

• Adsorption of Protein on the sensor platform:– Incubation of AT5G07010.1

– Adsorption of BSA

– Rinsing of the platform

– Recording of spectrum

88

Sample Preparation

Functionalization and Adsorption of

Protein and Antibody

Au nanoparticle film functionalized with

3-mercaptopropionic acid

Adsorption of Protein and Antibody

Glass

Glass

89

Spectra corresponding to the protein-antibody interaction:

A) spectrum of the functionalized substrate using Au that

was prepared in the lab B) spectrum of the antibody

adsorbed on the substrate C) spectrum of the previously

absorbed antibody followed by the adsorption of the protein

on the substrate

• Observed shift of +10 nm when antibody adsorbed

• After protein adsorption no additional shift but observed

shoulder around 600 nm

90

Spectrum corresponding to the protein sandwiched between two antibody

layers: A) Spectrum of the functionalized substrate with antibody and protein

adsorption – using Au that was prepared in the lab B) spectrum when an

additional antibody layer is adsorbed on the system corresponding to trace A

Results

Biomolecular Interactions cont’d

Sandwiched system: Using the previous system – additional

antibody layer adsorbed

Additional antibody layer results in shift of +10 nm

91

Results

Biomolecular Interactions

• ADDL is a biological molecule that may cause neurological dysfunctions relevant to memory –associated to Alzheimer’s disease

• Alzheimer’s disease leading cause of dementia in people over age of 65

• First patient diagnosed with Alzheimer’s disease was in 1906 – Aguste D

• Amyloid beta (Aβ) 42-amino acid peptide involved in neurotoxic assemblies

• Amyloid plaques causes:

– Neuronal degeneration

– Memory loss

– Progressive dementia

• (Aβ) protein monomers present in humans –not toxic until assemble into amyloid fibrils

• ADDLs are 3-24mers of (Aβ) monomer and are potent –

– Affect central nervous system

– Memory loss

• Elevated levels of ADDLs in autopsied brains of Alzheimer’s disease subjects

Interaction with Amyloid β–Derived Diffusible Ligands (ADDL)

92

Sample Preparation

Preparation of ADDL

• Preparation was done in collaboration with the

Department of Biology at Concordia University

• Prepared by the Lambert Protocol

• Two parts to the procedure:

– PART I: Monomerization (polymer that defragments

into monomers) by HFIP and storage of Aβ peptide

– PART II: Preparation of ADDL

93

Results

Biomolecular Interactions cont’d

• ADDL deposited on

functionalized gold

structures

• Left in contact with

sensor platform for

24 hours

• Large shift of

LSPR band

observed Δλ = 30nm

Δλ = λ in PBS without ADDL – λ in

PBS with ADDL

94

Results

Raman CharacteristicsDetection of Marine toxins using Au nanostructures: Gonyautoxin/Saxitoxin-e

GTX II: R1, R3 and R4= H, R2 = OSO3

GTX III: R1, R2 and R4= H, R3 = OSO3

Structures of both toxins similar – position of radicals different

Very toxic and an analytical method, without

complicated preparation, is very important.

The samples are simply drop-coated on the

gold nanostructure, dried and then,

measured.

Biomedical Sensors (SPR devices)

Spectrophotometry

15

20

25

30

35

40

0,2

0,4

0,6

0,8

1,0

1,2

250 500 750 1000 1250 1500 1750

0

2

4

6

8

10

12

On 5 nm Au network

Experimental condition

Filter : D1 (reduces the incident radion by 10 times)

A

C

On DCDR substrate


Filter : D1 (reduces the incident radion by 10 times)

Inte

ns

ity

(c

ou

nts

/se

c)

BOn DCDR substrate


Filter : No filter

Wavenumber (cm-1)

A. R. Hajiabol & M.Kahrizi, CSTC 2007

Comparing the Raman intensity to the toxin on DCDR

substrate (commercially available)

plasmons surface plasmon resonance plasmonic effects and...

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