evanescent wave based biosensors

EVANESCENT WAVE BASED
BIOSENSORS
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Annual Examination
Subject :Biosensors
Maximum Marks :60
Date :,Monday,30 November2009
Time : 9A.M to 12 P.M
Venue : Seminar Room (# 502),
Sanhakyon Building
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Outline
•Evanescent waves
•Applications:Biosensors
•Summary
•References
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What is an Evanescent Wave?
An evanescent wave is a near field standing wave with an intensity that
exhibits exponential decay with distance from the boundary at which the wave
is formed. Evanescent waves are a general property of wave-equations, and
can in principle occur in any context to which a wave-equation applies. They
are formed at the boundary between two "media" with different properties in
respect of wave motion, and are most intense within one-third of a wavelength
from the surface of formation.
In particular, evanescent waves can occur in the contexts of: optics and
other forms of electromagnetic radiation, acoustics, quantum mechanics
and "waves on strings".
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Plain wave at the boundary of two dielectrics.
Let us consider two dielectric media with refractive indices n1 and n2 respectively.
A plane wave strikes the boundary between the two media at an angle α.
Fig. 1. Plain wave at the boundary of two dielectrics
Taking into account boundary conditions between the dielectric
media we get:
Equations (1) lead us easily to the well known Snell's law.
The amplitudes of the reflected and refracted beams are described by the Fresnel
equations:
where n21=n2/n1. Superscripts _|_ and || denote perpendicular (TE) and parallel (TM)
polarization of the incident wave respectively.
Total internal reflection, critical angle
•
If n1 > n2 (the beam comes from the optically denser medium) and
angle of incidence α is greater than critical angle αc:
then sinγ > 1 and the total internal reflection occures. The light can no
longer propagate within less dense medium and is therefore totally
reflected. We can re-write the Fresnel equations:
where the phase θ is the solution of the following equations:
The described phenomenon was first recognized by Newton.
Evanescent wave
Surprisingly, there are still waves present in the less dense
medium. If we calculate the components of the wave vector for
the refracted wave we get:
One can see that the wave vector possesses components parallel (kx) and
perpendicular (kz) to the dielectrics' boundary. Equations (6) give us the
phase factor of the discussed wave:
The wave (called evanescent wave) propagates along the boundary and decays
exponentially with increasing the distance from the boundary.
"Evanescent" means "tending to vanish", which is because the intensity of evanescent waves
decays exponentially (rather than sinusoidally) with distance from the interface at which they are
formed. Evanescent waves are formed when sinusoidal waves are (internally) reflected off an
interface at an angle greater than the critical angle so that total internal reflection occurs.
The colors in the image at right indicate the instantaneous electric field magnitude of the incident
light. In this view, the plane of the page is the plane of incidence (contains the wave vector ki and the
normal to the interface, the latter indicated by the black line). Surfaces on which the electric field
magnitude is uniform are planes normal to the wave vector ki. Hence the incident light is a linearly
polarized plane wave (LPPW). As time progresses, these planes move at the speed of light in a direction
given by the wave vector ki. A LPPW is the type of wave produced by a laser.
The next image at right shows the reflected wave, which is also a LPPW. The direction of the
wave vector kr is determined such that the angle of incidence equals the angle of reflection.
A wave (called the refracted wave) also arises on the other side of the interface where the
reflection occurs. The three arrows in the sketch at left represent the 3 wave vectors for the
incident, reflected and refracted waves. All 3 wave vectors lie in the same plane (the plane of
incidence). The angle of incidence qi and the angle of refraction qr are related by Snell's law:
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Evanescent Wave Coupling
Coupling is usually accomplished by placing two or more electromagnetic
elements such as optical waveguides close together so that the evanescent
field generated by one element does not decay much before it reaches the
other element. With waveguides, if the receiving waveguide can support modes
of the appropriate frequency, the evanescent field gives rise to propagating
wave modes, thereby connecting (or coupling) the wave from one waveguide to
the next.
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Types of Evanescent Based Biosensors
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Biosensor
Analyte
Response
Analysis
Detection
Signal
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Sample handling/preparation
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1. SPR based biosensors
There are four basic methods to excite the SPR, as shown in
Fig.: prism coupling, waveguide coupling, fiber optic coupling and
grating coupling.
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Principle of Evanescent waveguide based biosensors
In waveguides, the light propagating through it consists of two components: (i) the guided field in
the core and (ii) the exponentially decaying evanescent field in the cladding. The evanescent field is
sensitive to the change in the refractive index of the cladding.
nCO > nCL
Clad (nCL)
Evanescent field
Core (n CO)
Fig. 2.1: Schematic of a typical waveguide.
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The distance to which the evanescent field extends beyond the core-cladding
interface is described by the penetration depth, which is the distance where the
evanescent field decreases to 1/e of its value at the core-cladding interface and is
mathematically described by the equation (1)[9].
Where x is distance from the fiber core, starting at x = 0 at the
core-cladding interface, E0 is the magnitude of the field at the interface,
and dp is the penetration depth. The penetration depth is given by (2) [9].
E0 exp(-x/d p) ..............(1)
E(x)
Where λ is the wavelength of the light source, θ is the angle of incidence of
the light at the core-cladding interface, nCO and nCL are the refractive indices (RI) of
the core and cladding, respectively. Fig. 2.1 depicts the cross-sectional view of a
waveguide cut along the longitudinal axis, and provides a graphical representation of
the penetration depth and a hypothetical ray of light propagating along the fiber.
Thus from equation (1) and (2) it can be concluded that the evanescent field is
sensitive to the change in RI of the cladding material. A variation in the RI of the
cladding material will lead to variation in the evanescent filed thus affecting the
intensity of the output.
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dp
λ
(
2
2
2π nCO sin θ
nCL
2
)
................(2)
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Penetration depth
We define the penetration depth d reflecting the decrease of the
evanescent wave amplitude in the "z" direction:
The d is a decreasing function of the angle of incidence and for α-αo~0,1° "d" is
of the order of a wavelength.
Many bio-physical processes like antibody-antigen and receptor-ligand binding lead
to change in RI. Hence in evanescent field based biosensors the cladding of the
fiber is removed and the exposed core is biologically tailored with the antibody or
receptor that is specific to the antigen or ligand to be estimated. A typical
evanescent field based waveguide based biosensor is shown in figure.
Clad (nCL)
Analyte solution (nAN)
Evanescent field
nCO > n AN
nCO > n CL
Core (n CO)
Schematic of a typical evanescent field based biosensor
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2. Interferometer-based biosensors
2.1. Mach-Zehnder interferometer
The operation principle of the integrated Mach-Zehnder interferometer (MZI) is
illustrated in the next slide. Coherent, single frequency, single polarization light from
a laser enters the single-mode input waveguide and is split equally at a Y-junction.
One branch has a window over the top of it allowing the evanescent field of that
branch to interact with the sample while the reference armis protected fromthe
sample with a thick cladding layer. The two branches recombine at the output,
resulting in interference, and a photo-detector measures the intensity. A change in
the RI at the surface of the sensor arm results in an optical phase change on the
sensing arm and a subsequent change in the light intensity measured at the
photodetector, as described by:
I(∆neff)‫ן‬cos(∆neffk0L)
where ∆neff, k0, and L are the RI change, the amplitude of wave vector, and the length of the
sensing region, respectively. Typically, increasing the length of the sensingwindowincreases the
sensing signal. However, note that because of the cosine-dependent intensity function, the
signal change is not easily resolvable near the maximum and minimum of the cosine function.
This is one penalty of using the MZI device as a sensor as compared to sensors that have a
linear intensity response.
Heideman et al. [R.G. Heideman, R.P.H. Kooyman, J. Greve, Sens. Actuators B Chem. 10 (1993)
209.] created a MZI on a silicon substrate with a Si3N4 waveguide and etched gratings for
input/output coupling. The RI detection limit was experimentally determined to be around
5×10−6 RIU. An antibody for human chorionic gonadotropin (hCG) was adsorbed onto one
channel, and hCG was then specifically detected. The experimental detection limit was 50 pM
hCG.
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2.2. Young’s interferometer:
In parallel to the development of integrated MZI sensors, another interferometric
technique based on an integrated Young’s interferometer (YI) has been used in a similar
way for biosensing. In a YI, the coherent, single mode, single polarization light at the input
is split into a reference arm and a sensing arm. Instead of recombining the arms as in the
MZI, the optical output of the two arms combines to form interference fringes on a
detector screen, such as a CCD. The spatial intensity distribution, I(x), along the detector
screen, x, is given as following,
where λ0 is the wavelength in vacuum, n the effective RI, δ represents a phase shift due
to a RI change, and d and f are the distance between the two arms and the distance
between the YI output and the screen, respectively. The equation shows that a phase
change on the reference arm causes a shift in the position of the interference fringes,
which can be analyzed quickly with a fast Fourier transform of the spatial intensity.
Specific detection of herpes simplex virus type 1 (HSV-1) was performed using an antiHSV-1 antibody immobilized on the interferometer surface, showing that 105 particles/mL
in serum could be detected within only 30min and that a DL of 103 particles/mL in
phosphate buffered saline could be achieved[A. Ymeti, J. Greve, P.V. Lambeck, T. Wink,
S.W.F.M.v. Hovell, T.A.M. Beumer, R.R. Wijn, R.G. Heideman, V. Subramaniam, J.S. Kanger,
Nano Lett. 7 (2007) 394].
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2.3. Hartman interferometer:
A third and very similar interferometry configuration that has been used for
biosensing is the Hartman interferometer (HI). In this configuration,
functionalization molecules are patterned in strips on top of a planar waveguide,
as shown in Fig. Light is coupled into and out of the planar waveguide using
gratings. Integrated optics is placed near the output of the chip to create
interference between pairs of functionalized strips. In the first biosensing
demonstration with the device, human chorionic gonadotropin (hCG) was detected
down to concentrations of 5 ngmL−1 [B.H. Schneider, J.G. Edwards, N.F. Hartman,
Clin. Chem. 43 (1997) 1757]
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2.4. Backscattering interferometry:
Typically, a Backscattering interferometry system consists of a coherent single
wavelength laser focused onto a small sensing area and a detector to analyze
the reflected intensity. Sub-wavelength structures on the sensing surface
result in interference at the detector.
Capture of proteins onto a selected part of the illuminated structure change
the intensity on the detector due to a phase change of the reflection from this
surface. This produces a sensing transduction signal.
This technique was used by Lin et al., who demonstrated one of the first
implementations of this concept using a porous silicon sensor surface [V.S.-Y.
Lin, K. Motesharei, K.-P.S. Dancil, M.J. Sailor, M.R. Ghadiri, Science 278 (1997)
840]. The top and bottom surfaces of the porous sensor serve as the reflecting
surfaces.When analytes are specifically captured by biorecognition molecules
immobilized inside the pores, a shift in the interference signal is observed. The
authors show detection of 2 pM target DNA using this sensor.
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3. OPTICAL WAVEGUIDE BASED BIOSENSORS
An optical waveguide based biosensor is a device that employs an optical
waveguide or a bundle of optical waveguides, as a platform for the
biological recognition element, and as a conduit for excitation of light
and/or the resultant signal.
Apart from the limit of detection (LOD) and selectivity, it is important to
recognize the advantages of waveguide based biosensors including
chemical-inertness, their compatibility to a wide range of surface
modifications, the potential for remote sensing, low-cost, and the ready
availability of inexpensive lasers and photo-detectors. Optical waveguide
based biosensors are classified by the biological recognition element
used for sensing.
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3. Optical waveguide based biosensors
3.1 Resonant Mirror (RM) design:
In a resonant mirror, the mode is leaky at the waveguide-substrate boundary, in
contrast to a conventional waveguide in which total internal reflection occurs at
both waveguide-solution and waveguide substrate boundaries. Fig. shows the
structure of the RM, where the high RI waveguide and the high RI substrate (or
prism) are separated by a metal layer or a low loss and low RI dielectric layer.
When the incident light is at the resonant angle, the light can be coupled strongly
into the high-index waveguide layer and has a strong reflection at the output side
of the RM. This resonant light travels along in the waveguide and has the
evanescent field outside the waveguide. As a result, the resonant angle is sensitive
to the RI change near the waveguide, which can be detected at the output side of
the RM. Note that, unlike SPR, which operates only at the TM mode, RM supports
both TE and TM modes, which have different resonant angles [N.J. Goddard, D.
Pollard-Knight, C.H. Maule, Analyst 119 (1994) 583 ]. The RM-based biosensor is
commercialized by NeoSensors with a detection limit on the order of 0.1 pgmm−2
[Website, http://www.neosensors.com ].
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3.2 Metal clad waveguide (MCWG) or metal clad leaky waveguide (MCLW):
The structure of the MCWG is schematically shown in Figure. In the MCWG, the light is
guided in a low RI layer and the metal layer works as a spacer to separate the low RI
waveguide and the high RI substrate, and to push more light into the solution layer to
increase the light-matter interaction and hence the sensitivity.
There are two types of MCWGs, dip type and peak type. When the imaginary part of the
metal dielectric constant is small and the metal thickness is on the order of tens of
nanometers, the MCWG is operated as a dip type, in which the reflection features a
characteristic resonant dip. On the other hand, when the imaginary part of metal dielectric
constant is high and the metal thickness is thin (only a few nanometers), the MCWG is
operated as a peak type and a characteristic peak emerges in the reflection.
Both the dip and peak can be used as a sensing signal in which the response is an angular
shift due to changes of the RI of the solution layer. Although both dip and peak types of
the MCWG have a lower sensitivity than SPR, they have a much narrower dip or peak,
making them a competitive sensing technology to SPR [N. Skivesen, R. Horvath, H.C.
Pedersen, Opt. Lett. 30 (2005) 1659].
A comparison between RM and the MCWG shows the MCWG is three times more sensitive
to the bulk RI change in the solution, indicating a much larger fraction of light in the
evanescent field [M. Zourob, S. Mohr, P.R. Fielden, N.J. Goddard, Sens. Actuators B Chem.
94 (2003) 304]. Therefore, the MCWG is very suitable for detection of cells that are
typically a few microns in size [N. Skivesen, R. Horv’ ath, S. Thinggaard, N.B. Larsen,
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H.C.Pedersen, Biosens. Bioelectron. 22 (2007) 1282].
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3.3 Reverse symmetry waveguides:
Reverse symmetry waveguides bear the similar design motivation, which is to push
more light into solution to increase the light interaction with large biomolecules,
such as cells. In the conventional waveguide geometry, the lower cladding layer
has a RI higher than that of solution, which usually consists of water and has a RI
of 1.33. Therefore, the waveguide mode has a light intensity more concentrated
toward the lower cladding layer, thus leaving less light to interact with the
analytes near to sensing surface. As shown in Fig. , in a reverse symmetry
waveguide, nanoporous silica is used as a lower cladding layer.
Nanoporous silica has a RI of 1.193, much lower than that of water. As a
result, more light can be concentrated near the sensing surface to enhance
the sensor sensitivity. Non-specific detection of Escherichia coli was
demonstrated with reverse symmetry waveguides. The detection limit is
estimated to be 60 cells/mm2 [R. Horv’ ath, H.C. Pedersen, N. Skivesen, D.
Selmeczi, N.B. Larsen, Opt. Lett. 28 (2003) 1233 ], a few hundred times
better than that in the RM [H.J. Watts, C.R. Lowe, D.V. Pollard-Knight,
Anal. Chem. 66 (1994) 2465 ].
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4. Optical ring resonator based biosensors
In a ring resonator, the light propagates in the form of whispering gallery modes (WGMs) or
circulating waveguide modes, which result from total internal reflection of light along the
curved boundary between the high and low refractive index (RI) media. Since the WGM and
circulating waveguide mode can be calculated using Mie theory ,for simplicity, we will use the
term “WGM” to describe both types of modes. The WGM has the evanescent field present at the ring resonator surface and responds to the binding of biomolecules.
In contrast to the straight waveguide, the effective light–analyte interaction length of a ring
resonator sensor is no longer determined by the sensor’s physical size, but rather by the
number of revolutions of the light supported by the resonator, which is characterized by the
resonator quality factor, or the Q-factor. The effective length, Leff, is related to the Qfactor by:
Leff =Qλ/2 πn
where λis the resonant wavelength and n is the RI of the ring resonator.
The WGM spectral position, i.e., resonant wavelength, λ, is related to the RI through the
resonant condition:
λ=2πrneff/m
where r is the ring outer radius, neff the effective RI experienced by the WGM, and m is an
integer. neff changes when the RI near the ring resonator surface is modified due to the
capture of target molecules on the surface, which in turn leads to a shift in the WGM
spectral position. Thus, by directly or indirectly monitoring the WGM spectral shift, it is
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possible to obtain both quantitative and kinetic information about the binding of molecules
near the surface.
5. Optical fiber based biosensors:
5.1. Fiber Bragg grating-based biosensors:
Fiber Bragg gratings (FBGs) are currently among the most popular of all fiberbased optical sensors for analyzing load, strain, temperature, vibration, and RI
[A.D. Kersey, M.A. Davis, H.J. Patrick, M. LeBlanc, K.P. Koo, C.G. Askins, M.A.
Putnam, E.J. Friebele, J. Lightwave Technol. 15 (1997) 1442].
Illuminating the fiber with two focused intersecting laser beams, RI
perturbations can be written into the fiber core that have periodicities (A) on
the order of the wavelength. The resulting structure functions as a band
rejection filter, reflecting a narrow band of light at the Bragg wavelength (λ B)
according to the following relationship:
λ B = 2neffA
where neff is the effective RI encountered by the fiber core mode. By
monitoring λ B, the system functions as a RI sensor, which serves as the
foundation for biochemical sensing functionality. Recently biosensing was also
carried out with a D-shaped fiber patterned with a FBG (Fig.) which shows a
detection limit of 10−5 RIU [T.L. Lowder, J.D. Gordon, S.M. Schultz, R.H.
Selfridge, Opt. Lett. 32 (2007) 2523.].
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6. Other optical fiber based label-free biosensors:
Aside from gratings, several other fiber-based technologies have been under development very
recently that take advantage of optical fiber’s cost effectiveness and its waveguiding capabilities.
One technology is the nanofiber shown in Fig., a silica fiber that is pulled under heat to a diameter
less than 1 µm [L. Tong, R.R. Gattass, J.B. Ashcom, S. He, J. Lou, M. Shen, I. Maxwell, E. Mazur,
Nature 426 (2003) 816 ]. The nanofiber has a very large evanescent field outside of the fiber due to
its small size, and therefore, is sensitive to the RI change. There are a few optical structures
developed based on the nanofibers, such as ring resonators, coils, and Mach-Zehnder
interferometers [M. Sumetsky, Y. Dulashko, A. Hale, Opt. Express 12 (2004) 3521, F. Xu, P. Horak, G.
Brambilla, Opt. Express 15 (2007) 7888, L. Tong, J. Lou, Z. Ye, G.T. Svacha, E. Mazur,
Nanotechnology 16 (2005) 1445.].It has been estimated that the detection limit for these sensors
can approach 10−7 RIU [F. Xu, P. Horak, G. Brambilla, Opt. Express 15 (2007) 9385] and the
sensitivity can reach 700nm/RIU with fiber radii of 300 nm [F. Xu, V. Pruneri, V. Finazzi, G.
Brambilla, Opt. Express 16 (2008) 1062].
Coupled optical fibers or fiber couplers, shown in Fig., are another fiber-based biochemical sensor
platform. In this case, two identical optical fibers are fused together and tapered to a diameter of 9
µm. The transmission spectrum is sinusoidal and shows a RI sensitivity close to 70 nm/RIU with a
detection limit of 4 10−6 RIU [H. Tazawa, T. Kanie, M. Katayama, Appl. Phys. Lett. 91(2007) 113901].
Tazawa et al. demonstrated this sensor’s ability to detect streptavidin with concentrations between
0.5 and 2 µgmL−1 using covalent surface chemistries.
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Total protein measurement using a fiber-optic evanescent wave-based
biosensor
A novel method and instrumental system to determine the total protein
concentration in a liquid sample is described.
It uses a fiber optic total protein sensor (FOPS) based on the principles
of fiber optic evanescent wave spectroscopy.
The FOPS applies a dye-immobilized porous glass coating on a multi-mode
optical fiber. The evanescent waves at the fiber optic core-cladding
interface are used to monitor the protein-induced changes in the sensor
element.
The FOPS offers a single-step method for quantifying protein
concentrations without destroying the sample. The response time and
reusability of the FOPS are evaluated. This unique sensing method
presents a sensitive and accurate platform for the quantification of
protein.
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Project,CNU Preejith et al. Biotechnology Letters 25: 105–110, 2003
Graph showing the UV-visible absorption
spectrum of: (a) Coomassie Brilliant Blue
(CBB) G-250, and (b) CBB when it binds with
bovine serum albumin in a solution of ethanol,
phosphoric acid and water.
Graph
showing the UV-visible absorption spectrum
of: (A)Coomassie
CBB in sol-gel film when it binds with bovine serum albumin.
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Brilliant Blue (CBB) G-250 immobilized in sol-gel film
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Calibration curves of bovine serum albumin,
haemoglobin, ovalbumin and cytochrome c.
Temporal response of the fiber optic
total protein sensor when tested with
bovine serum albumin at 20 µgml−1.
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Serum protein measurement using a tapered fluorescent
fibre-optic evanescent wave-based biosensor
The method is based on the principles of fibreoptic evanescent wave spectroscopy. The
biosensor applies a fluorescent dyeimmobilized porous glass coating on a multimode optical fibre. The evanescent wave’s
intensity at the fibre-optic core-cladding
interface is used to monitor the proteininduced changes in the sensor element. The
sensor offers a rapid, single-step method for
quantifying protein concentrations without
destroying the sample. This unique sensing
method presents a sensitive and accurate
platform for the quantification of protein.
Schematic diagram of the experimental set-up.
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The entire protein detection process was done in one minute, which
is significantly faster than the current dye based protein assay
method which takes about 30 min or more.
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Preejith et al. Meas. Sci. Technol. 17 (2006) 3255–3260
The fibre-optic total protein sensor developed in this study is based on the
variation
in
the
evanescent
wave
phenomenon
at
the
core-cladding
interface. The theoretical formalization of this concept can be found
elsewhere. In the biosensor design, an optical fibre is used as the
transduction element. A fluorescent emitting chemical is used to generate
an analyte-dependent, spectroscopically detectable signal within the sensing
region of the optical fibre. The NanoOrange, a merocyanine dye reagent,
is
virtually
nonfluorescent
in
aqueous
solution.
It
becomes
strongly
fluorescent at about 610 nm upon interaction with proteins when excited at
about 470–490 nm as used in this study. The chemical change that occurs
because of the interaction between the analyte and immobilized indicator
are measured by monitoring the electromagnetic radiation that returns
from the sensing unit. In this work, the authors describe a fibre-optic
evanescent wave based protein sensor to determine the total protein
concentration in a liquid sample.
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(a) Excitation spectrum of NanoOrange in sol–gel matrix.
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(b) Emission spectrum of NanoOrange in sol–gel matrix.
Preejith et al. Meas. Sci. Technol. 17 (2006) 3255–3260
Optimized dimensions (in mm) for the profiled fibre
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Graph showing the effect of incubation time on the leaching of entrapped dye.
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Preejith et al. Meas. Sci. Technol. 17 (2006) 3255–3260
Graph showing the optimization of NanoOrange concentration.
NanoOrange fluorescence with varying serum albumin concentration
is the spectral signature.
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Graph showing the effect of salt concentration on fluorescence emission.
Calibration curve for serum albumin using NanoOrange.
Preejith et al. Meas. Sci. Technol. 17 (2006) 3255–3260
A Rapid and Automated Fiber Optic–Based Biosensor Assay
For the Detection of Salmonella in Spent Irrigation Water Used in
the Sprouting of Sprout Seeds
A rapid and automated ber-optic biosensor assay for the detection of Salmonella in sprout rinse water
was developed in this study. Alfalfa seeds contaminated with various concentrations of Salmonella Typhimurium
were sprouted. The spent irrigation water was assayed 67 h after alfalfa seed germination with the RAPTOR
(Research International, Monroe, Wash.), an automated ber optic–based detector. Salmonella Typhimurium
could be positively identi ed in spent irrigation water when seeds were contaminated with 50 CFU/g. Viable
Salmonella Typhimurium cells were also recovered from the waveguides after the assay. This biosensor assay
system has the potential to be directly connected to water lines within the sprout-processing facility and to
operate automatically, requiring manual labor only for preventative maintenance. Therefore, the presence of
Salmonella Typhimurium in spent irrigation water could be continuously and rapidly detected 3 to 5 days before
the completion of the sprouting process.
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Use of KPL CSA-1 Salmonella Typhimuriumantibody or BiosPaci. c Salmonella
Typhimurium monoclonal antibody as a detection molecule in the biosensor assay.
Salmonella Typhimurium resuspended in PBS was automatically injected into the RAPTOR
coupon containing streptavidin and biotinylated KPL CSA-1 coated waveguides. The
detection antibody (at 10 mg/ml) consisted of Cy-5-labeled KPL CSA-1 Salmonella
Typhimurium antibody or Cy-5-labeled BiosPaci. c Salmonella Typhimurium monoclonal
antibody.
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Comparison of the RAPTOR biosensor assay with samples of buffer (PBS) and spent sprout irrigation
water (spent irrigation water) spiked with Salmonella Typhimurium. Samples were automatically injected
into the RAPTOR coupon containing streptavidin and biotinylated KPL CSA-1 coated waveguides. The
detection antibody (at 10 mg/ml) consisted of Cy-5-lableled BiosPaci.c Salmonella
Typhimurium monoclonal antibody. The DpA previous signal minus the detection limit was calculated as
described in ‘‘Materials and Methods.’’ (A) A representative assay for the detection of Salmonella
Typhimurium. Four waveguides were used for testing buffer or spent irrigation water samples. (B) The
normalized values for the mean of the DpA previous signal minus the detection limit when four
waveguides were interrogated in the biosensor assays. Error bars represent 61 SD for the mean of the
four waveguides.
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Covalent Attachment of Carbohydrate Derivatives to an Evanescent
Wave Fiber Bragg Grating Biosensor
Figure (a) Diagram of the JDSU fiber housing and positions of the etchant during primary and
secondary etches; (b) fiber diameter profile after secondary etch.
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Spectrum of the etched core
Fiber Bragg Grating sensor.
The feature in the reflection
spectrum
that
is
being
monitored is also shown.
Time dependence of glucose-siloxane
(1) attachment to the fiber Bragg
grating in 95% ethanol. Inset shows
the observed wavelength shift after
washing the fiber in water.
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Figure: Synthesis of glucose-siloxane conjugate and surface functionalization.
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Time dependence of glucose-siloxane (1) attachment to the fiber
Bragg grating in 95% ethanol. Inset shows the observed wavelength
shift after washing the fiber in water.
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Aptamers Based Biosensors
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Aptamers
•Aptamers, which are ssDNA or RNA oligonucleotides, can bind to their
targets due to their specific three dimensional structures; they offer
specific properties which favor them as new biorecognition elements for
biosensors
•They offer specific properties which favor them as new biorecognition
elements for biosensors.
•Aptamers are equal to monoclonal antibodies concerning their binding
affinities, but furthermore, they provide decisive
Advantages.
Aptamers have been developed for all classes of targets ranging from
small molecules to large proteins and even cells, proteins seem to be the
biggest group of target molecules.
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Protein Detection with Aptamer Biosensors
Aptamers have been developed for different applications. Their
use as new biological recognition elements in biosensors promises
progress for fast and easy detection of proteins. This new generation
of biosensor (aptasensors) will be more stable and well adapted to
the conditions of real samples because of the specific properties of
aptamers.
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Project,CNU
Strehlitz et al. Sensors 2008, 8, 4296-4307
Optical aptasensors
Optical transduction methods in aptasensors comprise, for example, the utilization
of
surface plasmon
resonance,
evanescent
wave
spectroscopy,
as
well
as
fluorescence anisotropy and luminescence detection.
Surface plasmon resonance (SPR) and evanescent wave based biosensors rely on
the change of optical parameters upon changes in the layer closest to the sensitive
surface. Since
the binding of, for example, proteins to a receptor layer of those
biosensors changes the refractive index of the layer,
the event of binding can be
detected and quantified in a label free way.
Binding of increasing amounts of human thrombin (0.5 … 75 nM) to the immobilized 3' biotinylated anti-thrombin aptamer
(15 nt, G-quartet), measured by use of the IAsys-system. Conditions: measurement in TA-buffer (20 mM TRIS-HCl, pH 7.4, 140 mM
NaCl, 5 mM KCl, 1 mM CaCl2, 1 mM MgCl2), time 5 min, Negative controls.. Elastase and HSA (25 nM each).
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Saturation curves generated from results in Fig.2. Each point represents
the measuring signal for one thrombin concentration after 5 min measuring
time. The fitted curve was used for the determination of Kd by nonlinear
regression analysis (Kd = 11.06 nM).
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Aptamer biosensors for protein detection
In the following table (Table 1), aptamer biosensors for different protein targets are presented and
listed according to the kind of nucleic acid of the aptamer (DNA or RNA), the transduction mode and
their reporter units (mediators, enzymes, dyes, etc.). Also, the achieved detection limits and
linear detection ranges are listed.
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A Fiber-Optic Evanescent Wave DNA Biosensor
Based on Novel Molecular Beacons
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Project,CNU
Liu et al. Anal. Chem. 1999, 71, 5054 5059
Dynamics of hybridization of MB evanescent
wave sensor: (a) 100 nM noncomplementary
oligonucleotide; (b) 100 nM one-basemismatched oligonucleotide; (c) 100 nM
complementary oligonucleotide.
Effect of metal ions on the hybridization reaction of
the immobilized MB with its target DNA molecule,
[DNA] 100 nM.
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Summary
•Low background,
•Low noise,
•Remote working geometry,
•Monitoring surface interactions
•Diagnostics
•Biotechnology
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References
•A Fiber-Optic Evanescent Wave DNA Biosensor, Based on Novel
Molecular Beacons, Xiaojing Liu and Weihong Tan, Anal. Chem. 1999, 71,
5054-5059
•A Rapid and Automated Fiber Optic–Based Biosensor Assay for
the Detection of Salmonella in Spent Irrigation Water Used in
the Sprouting of Sprout Seeds, MARIANNE F. KRAMER* AND DANIEL
V. LIM, Journal of Food Protection, Vol. 67, No. 1, 2004, Pages 46–52
•Protein Detection with Aptamer Biosensors, Beate Strehlitz , Nadia
Nikolaus and Regina Stoltenburg, Sensors 2008, 8, 4296-4307; DOI:
10.3390/s8074296Sensors 2008, 8, 4296-4307; DOI:
10.3390/s8074296
•Serum protein measurement using a tapered fluorescent fibre-optic
evanescent wave-based biosensor, P V Preejith1, C S Lim1, and T F
Chia, Meas. Sci. Technol. 17 (2006) 3255–3260
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