Biosensor Presentation

8/8/2019 Biosensor Presentation

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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




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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.




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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).




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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




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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.




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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!




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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.




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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.




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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.




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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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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)




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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.




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Fig. 2:Principle of

Photometric

Biosensor




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Fig. 3: Principle of Photometric Biosensor




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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




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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




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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).




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Electrochemical Biosensors:



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:



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.




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Piezoelectric Biosensors:



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:



Fig. 8:Global Market

of Biosensors


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Time to Question



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