biosensor presentation
TRANSCRIPT
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Whats Biosensor?
Principle of Biosensors
Role of Enzyme
Types of Biosensors
Applications
Markets
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
http://Sensors.blogfa.com Email: [email protected]
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Whats Biosensor?
A biosensor is an analytical device which
converts a biological response into an
electrical signal
Fig. 1
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Parts of Biosensor:
A biosensor has two components: a receptor and
a detector. The receptor is responsible for the
selectivity of the sensor. Examples includeenzymes, antibodies, and lipid layers. The
detector, which plays the role of the
transducer, translates the physical or chemical
change by recognizing the analyte and relaying
it through an electrical signal. The detector
is not selective. For example, it can be a pH-
electrode, an oxygen electrode or apiezoelectric crystal.
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Principle of Operation (See Fig 1):
The biocatalyst (a) converts the substrate
to product. This reaction is determined by
the transducer (b) which converts it to an
electrical signal. The output from the
transducer is amplified (c), processed (d)
and displayed (e).
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
http://Sensors.blogfa.com Email: [email protected]
What means by Biosensor?
The term 'biosensor' is often used to cover
sensor devices used in order to determine
the concentration of substances and other
parameters of biological interest even where
they do not utilize a biological system
directly.
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To have a successful biosensor:
1. The biocatalyst must be highly specific for thepurpose of the analyses and be stable undernormal storage conditions.2. The reaction should be as independent of suchphysical parameters as stirring, pH,temperature
3. The response should be accurate, precise,reproducible and linear over the usefulanalytical range. It should also be free fromelectrical noise
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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To have a successful biosensor (continued):4. The response should be accurate, precise,reproducible and linear and free from
electrical noise.5. The probe must be tiny and biocompatible, havingno toxic or antigenic effects.6. The complete biosensor should be cheap, small,portable and capable of being used by semi-skilled operators.7. There should be a market for the biosensor.
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Whats Enzyme?
Enzymes are biological
catalysts: this means that they
speed up the chemical reactionsin living things. Without
enzymes, our guts would take
weeks and weeks to digest ourfood, our muscles, nerves and
bones would not work properly
and so on - we would not be
living!
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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What Enzymes are made of?
All enzymes are made of protein; that is why
they are sensitive to heat, pH and heavy metal
ions. Unlike ordinary catalysts, they arespecific to one chemical reaction. An ordinary
catalyst may be used for several different
chemical reactions, but an enzyme only worksfor one specific reaction.
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Why we need Enzyme?
The biological response of the biosensor is
determined by the biocatalytic membrane which
performs the conversion of reactant (thingwhich responds to a stimulus) to product.
Immobilized (unable to move ) enzymes possess
a number of advantageous features which makesthem particularly applicable for use in such
systems.
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Need to Immobilized Enzyme:
Many enzymes are intrinsically stabilized by
the immobilization process, but even where
this does not occur there is usuallyconsiderable apparent stabilization. It is
normal to use an excess of the enzyme within
the immobilized sensor system. This gives acatalytic excessive which is sufficient to
ensure an increase in the apparent
stabilization of the immobilized enzyme.
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Type of Biosensors:
1. Photometric
2. Electrochemical
3. Piezoelectric
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Photometric Biosensors:
1. Based on the phenomenon of surface Plasmon
resonance
2. Utilizes a property shown of materials;
specifically that a thin layer of gold on a
high refractive index
3. Glass surface can absorb laser light,
producing electron waves (surface Plasmon) on
the gold surface
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Fig. 2:Principle of
Photometric
Biosensor
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Photometric Biosensors:
Plasmon Biosensors operate using a sensor chip
consisting of a plastic cassette supporting a
glass plate. One side is coated with amicroscopic layer of gold to contact the
optical detection apparatus of the instrument.
The opposite side is contacted with amicrofluidic flow system. to create channels
across which reagents can be passed in
solution. See Fig. 2 and 3)
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Photometric Biosensors:Light, at a fixed wavelength is reflected off the goldside of the chip and detected inside the instrument.This induces the disappearing wave to enter through theglass plate and someway into the liquid flowing over thesurface. Refractive index at the flow side of the chipsurface has a direct influence on the behavior of thelight reflected off the gold side. Binding to the flowside of the chip has an effect on the refractive indexand in this way biological interactions can be measuredto a high degree of sensitivity with some sort ofenergy.
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Fig. 2:Principle of
Photometric
Biosensor
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Fig. 3: Principle of Photometric Biosensor
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Photometric Biosensors:
Other optical biosensors are mainly based on
changes in absorbance or fluorescence of an
appropriate indicator compound and do not needa total internal reflection geometry. For
example, a fully operational prototype device
detecting casein in milk has been fabricated.
The devices is based on detecting change in
absorption of a gold layer (See Fig. 4)Ha Minh Hiep et al: A localized surface plasmon resonance based immunosensorfor the detection of casein in milk, Science and Technology o f Advanced M aterials
8 (2007) 331338
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
http://Sensors.blogfa.com Email: [email protected]
Fig. 4Ha Minh Hiep et al: Alocalized surfaceplasmon resonancebased immunosensorfor the detection ofcasein in m ilk, Scienceand Technology ofAdvanced Materials 8(2007) 331338
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Electrochemical Biosensors:Based on enzymatic catalysis of a reaction to produce orconsume electrons (Redox enzymes)Sensor substrate contains three electrodes, a referenceelectrode, an active electrode and a sink electrode. Anauxiliary electrode (or counter electrode) may also be presentas an ion sourceThe target analyte is involved in the reaction that takesplace on the active electrode surface to produce ionsIons produced create a potential which is subtracted from thatof the reference electrode to give a signal. We can eithermeasure the current (rate of flow of electrons is nowproportional to the analyte concentration) at a fixedpotential or the potential can be measured at zero current
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
http://Sensors.blogfa.com Email: [email protected]
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Fig. 4: A simple potentiometricbiosensor. A semi-permeable
membrane (a) surrounds the
biocatalyst (b) entrapped next tothe active glass membrane (c) of a
pH probe (d). The electrical
potential (e) is generated between
the internal Ag/AgCl electrode (f)bathed in dilute HCl (g) and an
external reference electrode (h).
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Electrochemical Biosensors:
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
http://Sensors.blogfa.com Email: [email protected]
The main body of the biosensor is ap-type silicon chip with two n-typesilicon areas; the negative sourceand the positive drain. The chip isinsulated by a thin layer (0.1 mmthick) of silica (SiO2) which formsthe gate of the FET. Above this gateis an equally thin layer of sensitive material (e.g.tantalum oxide). When a potential is applied between theelectrodes, a current flows through the FET dependent uponthe positive potential detected at the ion-selective gateand its consequent attraction of electrons into thedepletion layer.
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Piezoelectric Biosensors:It is well known that the resonant frequency
of an oscillating piezoelectric crystal can be
affected by a change in mass at the crystalsurface. Then Piezoelectric immunosensors are
able to measure a small change in mass. The
basic equations describing the relationship
between the resonant frequency of an
oscillating piezoelectric crystal and the mass
deposited on the crystal surface
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Piezoelectric Biosensors:
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Fig. 6:Principle of
Piezoelectric
sensors
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Piezoelectric Biosensors:They utilize crystals which undergo an elastic
deformation when an electrical potential is
applied. An alternating potential produces astanding wave in the crystal at a
characteristic frequency. This frequency is
highly dependent on the elastic properties of
the crystal, such that if a crystal is coated
with a biological recognition element the
binding of a target analyte to a receptor will
produce a change in the resonance frequency.
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Piezoelectric Biosensors:
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
http://Sensors.blogfa.com Email: [email protected]
Fig. 7: Impedanceanalysis is based on
electrical conductance
curve. The central
parameters of
measurement are theresonance frequency and
the bandwidth w.
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Applications: Glucose monitoring in diabetes patients
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Markets:
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
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Fig. 8:Global Market
of Biosensors
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Time to Question
M.H. Shahrokh Thick-Film Lab, Electronics Dept., Engs. Faculty, UPM
http://Sensors.blogfa.com Email: [email protected]