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BY
Sheikhasinah.S.M
Poornimadevi.S

 The first biosensor was described in 1962 by Clark and
Lyons who immobilized glucose oxidase (GOD) on an
amperometric oxygen electrode surface semipermeable
dialysis membrane in order to quantify glucose
concentration in a sample directly.
 They described how "to make electrochemical sensors
(pH, polarographic, potentiometric or conductometric)
more intelligent" by adding "enzyme transducers as
membrane enclosed sandwiches".

 Based on bioreceptors
 Enzyme biosensor
 Microbial biosensor
 Affinity biosensor
 Based on transducer
 Potentiometric
 Amperometric
 Conductometric
 Optical Acoustic or piezoelectric etc.

 Other names immuno-sensors,chemical
canaries, biochips, bio-computers.
 Principle::
Many chemical reactions produce or
consume ions or electrons which in turn cause
some change in the electrical properties of the
solution which can be sensed out and used as
measuring parameter.
 Classification :
(1) Amperometric biosensor
(2) Conductometric/Impedimetric biosensor
(3) Potentiometric biosensor

 Uses:
 Detection of Hybridized DNA
 DNA- binding Drugs &
 Glucose Concentration.
 Required Characteristics:
 Good Sensitivity
 Utility
 Low detection limit
 Field portability
 Low Cost
 Reliability
 Accuracy

 Measures Electrical Conductance/Resistance of
the solution.

 Enzymatic glucose biosensors
a. First generation glucose biosensor
b. Second generation glucose biosensor
c. Third generation glucose biosensor
 Non-enzymatic glucose biosensors

 High Sensitivity Biosensor.
 Measured Parameter – Current
 The simplest amperometric biosensors in
common usage involve the Clark oxygen
electrode.

 Developed by Updike and Hicks
 Enzyme Glucose oxidase catalyze the oxidation of
glucose by molecular oxygen producing
glucolactone and hydrogen peroxide.
 In order to work as a catalyst, GOx requires a
redox cofactor –flavin adenine dinucleotide (FAD),
works as an initial electron acceptor and is reduced
to FADH2.
Glucose + GOx –FAD  Glucolactone + GOx – FADH2

 The cofactor is regenerated by reacting with oxygen,
leading to the formation of hydrogen peroxide
GOx – FADH2 + O2  GOx – FAD + H2O2
• Hydrogen peroxide is oxidized at a platinum electrode.
The number of electron transfers, at electrode surface is
directly proportional to the number of glucose molecules
present in the blood.
H2O2  2H+ + O2 + 2 e-
• Three strategies used for the electrochemical sensing of
glucose are
 By measuring oxygen consumption
 By measuring the amount of hydrogen peroxide
produced by the enzyme reaction

Schematic diagram of a simple amperometric biosensor.

 Working Principle – When ramp voltage is applied
to an electrode in solution, a current flow occurs
because of electrochemical reactions.
 Measured Parameter – Oxidation / reduction
Potential of an Electrochemical rxn.
 This consists of an immobilised enzyme membrane
surrounding the probe from a pH-meter where the
catalysed reaction generates or absorbs hydrogen
ions. The reaction occurring next to the thin
sensing glass membrane causes a change in pH
which may be read directly from the pH- meter's
display.

Examples of Potentiometric Biosensor. Many
biosensors have been developed using pH sensor
as the base transducer. Some of the examples and
their performances are illustrated in the following.
1. Penicillin biosensor
 Penicillinase
 Penicillin -----------------------> penicillic acid + H+
2. Glucose biosensor
 Glucose oxidase
 Glucose ------------------------> gluconic acid + H2O2
3. Urea biosensor
 Urease
 Urea ----------------------------- 2 NH4
+ +NCO3
-

I. Food Analysis.
II. Study of Biomolecules & their Interaction.
III. Drug Development.
IV. Crime Detection.
V. Medical Diagnosis (Clin&Lab).
VI. Environmental Field Monitoring.
VII. Quality Control.
VIII. Industrial Process Control.
IX. Detection Systems for Biological Warfare Agents.
X. Manf. Of Pharmaceuticals & Replacement organs.
XI. Detection of viral, fungal, bacterial diseases of
plants.

o Pregnancy Test
o Old time - coal miners’ Biacore Biosensor
o light-addressable potentiometric sensors
(LAPS).- Used to detect Francisella tularensis

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