Download Surface plasmon resonance sensing

Surface plasmon resonance sensing
Surface plasmon waves extend few hundred nanometres above the metal
film. They are affected by the refractive index in this region.
Z
Evanescen
t Field
Dielectric
Surface
Plasmon
Metal
≈ 50nm
Prism
θi = θsp
θ
θ
i
r
θi = θr
θi > θc

 
 sin  
c
c  
1
1
Fi  f ()   i ,
i  1,, n
Gi  g ()  i ,
i  1,, n
Di  Fi  Gi
Surface plasmon
resonance sensors are
important for
ultrasensitive
immunoassays
with applications in
health diagnostics
2
1
1
2
Conventional sensor system
Principle of immunoassays:
• Reactions between two protein
molecules can be extremely specific.
• One type of molecule (antibody) can
be immobilised on gold sensor surface
• The second (antigen) will bind
changing the refractive index
• This change is detected by changed
angle of surface plasmon resonance
Simulation based on n-layer system
p-polarised light
To detector
z
Incident
zn-1
Reflected
n (εn)
n-1 (εn-1)
zj
zj-1
z1
j+1 (εj+1)
j (εj)
surface plasmon at
interface, wavevector k||
dj = zj – zj-1
j-1 (εj-1)
• Simulation based on Fresnel
reflectivity equations for an nlayered system
• System consisted of a BK7
hemispherical prism, a 50nm
gold layer and an analyte layer
• Simulation produced R vs θ
curves from system parameters
(incident light wavelength λ and
angle θ, layer thicknesses d and
permittivities ε)
2 (ε2)
1 (ε1)
Transmitted
x
Source: S. Orfanidis, “Electromagnetic waves and antennas” pp.81-108
R.U.S. Kurosawa et al, PRB 33,789 (1986)
2
R  rn ,l 
rn ,n 1  rn 1,l e
2 idn 1k zn1 2
1  rn ,n 1rn 1,l e 2idn 1k zn1
Surface Plasmon Resonance Sensing System
Opportunities:
Challenges:
• LED must be stable, preferably
at a
level 10-7
• Detector response must be linear, with
similar accuracy
• Readout must be very fast
• Surface plasmons probe ultrathin regio
(monolayer is enough)
• System can use inexpensive componen
can run on Palm
• Sample can be extremely small
(microfluidics)
Statistical hypothesis testing for
sensitivity improvement

Two SPR curves Fi and Gi
produce difference curve Di

From the average value of D
and the variance S define a
standardised Z value

Central Limit Theorem states
that Z has approximately
standard normal distribution
Fi  f ()   i ,
i 1

Hypothesis: that two curves Fi
and Gi are the same
Gi  g ()  i ,
i

Choose to reject hypothesis for
significance level =0.05:
(Z>1.96)

Di  Fi  Gi
Probability that this was wrong
decision is less than 5%
1
D
n
n
D
k
k 1
1 n
S 
( Dk  D ) 2
n  1 k 1
2

D
Z
n
S
Test parameters used
• Input wavelength 632.8nm
• 3 layered system (BK7 glass
prism, 50nm gold layer,
analyte layer of water and
isopropanol solutions)
• Collection device - array
detector from Ames Photonics
Inc.
–
–
384 simulation points (3mm
laser diameter over 1024
pixels contained in 7.99mm)
Noise standard deviation 3 x
10-6 (based on noise specifics
for detector, total
integration time of 100s with
1ms integration time)

Test applied to curve regions within
front edge of reflectance curve
Nanotechnology approach for the optical
sensing of trace pathogens
• Aim:
Develop a new optical
based sensor
technology for rapid
detection of trace
pathogens and
chemicals in the
environment.
• Novel approach:
Apply surface nanopatterning techniques
to a Surface Plasmon
Resonance (SPR)
sensing system to
achieve unprecedented
sensitivity levels
Surface plasmons are
electromagnetic waves
excited by light in
metal films.
Surface plasmons
sense the analyte
Sensor readout
Nanostructures
increase device
sensitivity
Examples of nanostructures
105.16 nm
5 µm
52.58 nm
0 nm
5 µm
2.5 µm
2.5 µm
0 µm
0 µm
Rigorous coupled wave analysis for modelling nanomodified surface plasmon based sensing systems
EXAMPLES OF NANOMODIFIED SENSOR SETUPS
Nanomodification of SPR sensors is achieved through the binding of noble metal colloids near the sensor surface
or through direct nanostructuring of the sensing surface via lithographic or direct writing processes. Examples of
two nanomodified SPR setups are presented below.
(b)
(a)
1.
2.
3.
4.
1.
2.
3.
4.
Figure 2: Two nano-modified SPR sensor configurations reported in the literature:
(a)
1. Prism for coupling to SP, 2. Thin metal layer(s), 3. Self Assembled Monolayer (typically 1,6-hexanedithiol or 2mercaptoethylamine, 4. Attached metal colloids (typically Au or Ag, between 10 nm and 50 nm diameter) [11]
(a)
1. Prism for coupling to SP, 2. Thin metal layer(s), 3. Metal nanowires formed usually by nanolithography, 4. Self
Assembled Monolayer either on top of structure or between nanowires and thin metal layers [12]
MODEL:
pproach was developed by Moharam and Gaylord [20] and is a full vectorial solution of Maxwell's equations.
proach is based on the following steps:
entation of periodically varying permittivity (for example in a grating structure) using Fourier series expansion:
 ( x, z )   ( x  , z )   m ( z ) exp( j 2mx  )
m
cation of Maxwell’s wave equations for incident light polarisation, through consideration of the orientation to the electromagne
to the periodicity of the grating, using vector identities:
  
2 E   E    k 2 ( x, z ) E  0
 


2 H 
   H  k 2 ( x, z ) H  0 *

n * is simplified for p-polarised (transverse magnetic) light incidence as (from figure 1) H is perpendicular to  so   H  0 an
he vector identity     H  (  H )  (  ) H  ( H  )  H  (   ) and     0 producing:
  
2 H  
   H  k 2 ( x, z ) H  0



ctric or magnetic field within the grating is written using a space-harmonic representation:
H ( x, z ) 

U ( z) exp(  jk
xi x )
i
i  
Fourier harmonics within the grating are a function of the grating perpendicular direction only, this allows the Maxwell equatio
o be written as a set of ordinary coupled differential equations with constant coefficients (in the case of a rectangular grating)
lue approach to their solution.
ontinuity considerations of the electromagnetic field at the boundary of the grating, the Fourier harmonics may be matched to
on of the fields beyond the grating region to determine the efficiency of each propagating order.
ry conditions for p-polarisation are:
H  ( x, z) z0  H  ( x, z) z0
1

H  ( x, z )

1

H  ( x, z )
1.0
0.9
Simulation results
θ
0.8
Prism
Gold
SAM
H
Reflectance
0.7
These simulations were carried
out using DiffractMOD, an RCWA
based software package from
RSoft
W
Λ
0.6
0.5
Nanowire period:
200 nm
400 nm
600 nm
800 nm
1000 nm
0.4
0.3
0.2
No nanowires:
No SAM
SAM
0.1
0.0
40
42
44
46
48
50
Angle (degrees)
Reflectance results showing the effect of variation of
nanowire period Λ. Insert: Diagram of setup under consideration.
1.0
0.9
θ
4.0
0.8
Prism
1.4
Gold
Nanowire size:
10 nm
20 nm
30 nm
40 nm
50 nm
60 nm
0.4
0.3
0.2
No nanowires:
No SAM
SAM
0.1
0.0
40
42
44
46
48
50
52
54
Sensitivity (figure of merit)
Reflectance
W
0.6
0.5
3.5
SAM
H
0.7
1.2
3.0
1.0
2.5
0.8
2.0
0.6
1.5
1.0
0.4
0.5
0.2
Angle (degrees)
0.0
0.0
0
200 400 600 800 1000
Nanowire period (nm)
Reflectance results showing the effect of variation of
nanowire width and height (W, H).
Insert: Diagram of setup under consideration.
0
10
20
30
40
Nanowire size (nm)
Surface plasmon coupled emission
514 nm
• Fluorescence emission is strongly directional
• Applications for fluorescence bioassays
R 101
In PVA
Gold
Film
514 Notch
Filter
Optical Fiber
Surface Plasmon Coupled
Emission
Evanescent
SP Field
SPCE Coupling
Layer ~ 200 nm
Excitation scheme adapted
for microscopy
Silica
Gold
SP Wave
SPCE
Cone
Silica Protective
Layer
Sample
Glass
Slide
TIRF
SPR
SPCE
Objective
SPR
SPCE
Semitransparent
Metallic Film
g
Two photon
SPCE
demonstrated
SPCE INTENSITY at 665 nm, a.u.
400
Schematic diagram of a model bioassay
BUFFER
SERUM
WHOLE BLOOD
300
200
100
0
640
680
720
WAVELENGTH, nm
Feasibility of bioassays
in dense media
Relevant publications
• “Plastic Versus Glass Support for an Immunoassay on Metal-Coated Surfaces in
•
•
•
Optically Dense Samples Utilizing Directional Surface Plasmon-Coupled Emission
Evgenia G. Matveeva, Ignacy Gryczynski, Joanna Malicka, Zygmunt Gryczynski, Ewa
Goldys, Joseph Howe, Klaus W. Berndt, and Joseph R. Lakowicz, Journal of
Fluorescence vol.15, no.6 : 865-71, Nov. 2005
“Directional two-photon induced surface plasmon-coupled emission” Gryczynski,
Ignacy; Malicka, Joanna; Lakowicz, Joseph R.; Goldys, Ewa M.; Calander, Nils;
Gryczynski, Zygmunt, Thin Solid Films, 491(1-2), 173-176, (2005).
“Ultrasensitive detection in optically dense physiological media: applications to
fast reliable biological assays” . Matveeva, Evgenia G.; Gryczynski, Ignacy; Berndt,
Klaus W.; Lakowicz, Joseph R.; Goldys, Ewa; Gryczynski, Zygmunt. Proceedings of
SPIE-The International Society for Optical Engineering (2006), 6092 125-133.
“Detection limit improvement of surface plasmon resonance based biosensors
using statistical hypothesis testing”, Barnett, Anne; Goldys, Ewa M.; Dybek, Konrad,
Proceedings of SPIE-The International Society for Optical Engineering (2005),
5703(Plasmonics in Biology and Medicine II), 71-78. “Strategies for noise reduction
and sensitivity increase for a Surface Plasmon Resonance (SPR) based biosensing
system”, A. Barnett, E.M. Goldys, K. Dybek. OWLS Conference, Optics Within Life
Sciences” Melbourne 28 Nov 2004 – 1 Dec 2004