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BIOSENSORS IN MONITORING

OF BIOPROCESS

SAJINA.KUMARI.S

3rd sem biotechnology

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Fermentation process are complex

systems, with many interacting variables Continuous monitoring of parameters such

as pH , temperature , and dissolved

oxygen levels, with direct feedback to

control systems, is standard even in the

smallest bioreactors and the enabling

technologies

Monitoring of other parameters, such asthe levels of substrates and products

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BIOSENSORS IN PROCESS

MONITORING The common theme is that a biosensors

couples a biological element , which

provides specific recognition of the targetanalyte, to a transducer, which generates

an electrical signal

Electrical signal can be directed to a digital

readout, or can be logged or used as an

input to a control system

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The biological recognition element may be

an enzyme, an antibody or similar bindingmolecule, or a living cell

Transducer may detect a redox reaction,light emission, altered levels of an ion, a

luminescent or fluorescent signal, or achange in mass associated with a surface

The aim of a biosensor is to provide arapid, highly specific, quantitativeresponse , with a minimal or zerorequirement for sample preprocessing

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The main types of recognition element

used are enzymes and antibodies

Biosensors are also applied to the

detection of many other analytes in the

clinical samples, pollutants, food industry,

metabolites during fermentation process

FIA automatic abstraction of samples

from the test system and their injection into

flow of a carrier liquid, which is constantlypassed through the detection element

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TRANSDUCTION METHODS

Amperometric - electrode is held poised at

a constant voltage relative to a reference

electrode usually Ag/AgC

l) by the use of acircuit known as a potentiostat

Potentiometric an ion selective electrode

is used, and the build-up of the appropriate

ion causes a change in potential with verylittle current flow

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Thermal- extremely sensitive temperature

sensing element (thermistor) used to

detect the increase in temperature due to

heat released by an enzyme- catalyzed

reaction

Optical- based on the transmission of lightalong an optical fiber to a detector.

Surface Plasmon Resonance(SPR)-It is

applied to the detection of small changesin mass due to ligand binding in a film of

immobilized antibodies

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Piezoelectric- In

this case, the film

is immobilized on

the surface of a

piezoelectric

crystal such asquartz, detection

based on changes

in the mechanicalproperties of the

surface film as its

mass increases.

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CATALYTIC BIOSENSORS: Enzymes

as Biological Sensing Elements

Enzymes form most widely used

Biosensors- Oxidoreductase : oxidize orreduce the substrate , they are involved in

the movement of electrons and lend to

amperometric detection methods

Some cases enzyme based system

require additional small molecules such as

co-factors or co-substrates

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AFFINITY BIOSENSORS: Antibodies as

Biological Detection Elements

Biosensors based on antibodies are

sometimes immunosensors Two types of Label-based assay

Sandwitch assay

Competitive assays

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IMMOBILIZATIONOF THE BIOLOGICAL

RECOGNITION ELEMENT

ADSORPTION- enzyme or antibody exposed

to the surface and attaches by adsorption

RETENTION WITHIN A MEMBRANE-BOUNDED

COMPARTMENT-electrode surrounded by

dialysis membrane, enzyme solution is

contained between this and anotherdialysis membrane

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INDIRECT AFFINITY SENSORS-Optical and

Electrical biosensors based on antibodies

Use of antibodies labeled with horseradish

peroxidase (HRP), such antibodies areused for colorimetric or fluorimetric

detection based on reaction of HRP with

luminol or chromogenic substrates( 4-amino-phenazone

When used in biosensors it can be

detected optically by chemiluminescence

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Using aptamersrather than using a

antibodies in a sandwich-type assay The captured aptamer was immobilized on

a gold electrode surface, and the detection

aptamer was labeled with PQQ-dependent

glucose dehydrogenase .

Amout of enzyme captured near the

electrode surface was detected

amperometrically following the addition ofglucose

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DIRECT AFFINITY DETECTION USING

SURFACE PLASMON RESONANCE ANDPIEZOELECTRIC BIOSENSORS

Here the binding of ligand to immobilizedcapture molecules is detected directly by

monitoring the amount of mass associated

with the capture surface

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Atttachment of large ligands to the capture

molecules increases the mass of the filmto a detectable degree

The main method used for such systems

are surface plasmon resonance(SPR) and

piezoelectric transduction, mainly quartz

crystal microbalance(QCM)

Surface Plasmon Resonance(SPR) is an

effect in which a beam of laser light isshown through a transparent medium

coated with a thin film of gold, with a fluid

layer on the other side of the gold film.

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Some reports have also described

integration of multiple sensors of differenttypes in a single chip

For eg: construction of an SPR

immunosensors chip for human IgG, alsobearing integrated amperiometric sensors

for glucose and lactate ; this was used for

simultaneous on-line monitoring of

glucose, lactate, and IgG in a cell culture

bioreactor

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Acoustic wave (piezoelectric) systems

used to measure mass changes due to

ligand binding in a film of immobilized

antibody

This detection is based on changes in the

nature of vibration of a piezoelectricmaterial such as quartz when an electrical

potential is applied

In this case, the antibody film isimmobilized on the surface of a

piezoelectrical crystal

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REFERENCES

Principlesoffermentationtechnology-

PeterF. Stanbury, Allan Whitaker

Fermentationmicrobiologyandbiotechnology- Mansi El-Mansi, Charles

F. A. Bryce