Leland Clark invented the Clark oxygen electrode, a pivotal biosensor that allows real-time monitoring of blood oxygen levels during surgery. A biosensor consists of a biological material like an enzyme or antibody immobilized on a transducer. When an analyte binds to the biological material, it produces a signal like electrons that are converted by the transducer into measurable electrical signals. Biosensors have important applications in clinical diagnostics like glucose monitoring, environmental monitoring of pollutants, and industrial processes like fermentation. Their low cost, small size, and sensitivity make them useful analytical tools.

1. BY - NEETIKA MEHTA
BSc MICROBIOLOGY( Hons.)
2ND YEAR

2. • Father of Biosensors Leland C. Clark invented the Clark Oxygen Electrode,
a pivotal device that allows real-time monitoring of patient’s blood
oxygen levels and has made surgery Safer and more successful for
millions around the world .
• BIOSENSOR
A biosensor is an analytical device containing an immobilized biological
material (enzyme, antibody, nucleic acid, hormone, organelle or whole
cell) which can specifically interact with an analyte and produce
physical, chemical or electrical signals that can be measured. An analyte
is a compound (e.g. glucose, urea, drug, pesticide) whose concentration
has to be measured. Biosensors basically involve the quantitative
analysis of various substances by converting their biological actions
into measurable signals.

3. • The biological material is immobilized and a contact is made between the
immobilized biological material and transducer.
• The analyte binds to the biological material to form a bound analyte
which in turn produces the electronic response that can be measured.
• Sometimes the analyte is converted to a product which could be associated
with the release of heat, gas(oxygen), electrons or hydrogen ions. The
transducer then converts the product linked changes into electrical signals
which can be amplified and measured.

4. • Analyte diffuses from the solution to
the surface of the Biosensor.
• Analyte reacts specifically and
efficiently with the biological
component of the biosensor.
• This reaction changes the
physicochemical properties of the
Transducer surface.
• This leads to a change in the
optical/electrical properties of the
Transducer surface.
• The change in the optical/electrical
properties is measured/converted into
electrical signals , which is detected.

6.  High specificity and selectivity (low interference).
 Sufficient sensitivity and resolution.
 Sufficient accuracy and repeatability.
 Sufficient speed of response .
 Sufficient dynamic range.
 Insensitive to environmental interference or their
effects must be compensated.

7. 1. Analyte
2. Biological elements
3. Transducer
4. Processor
5. Monitor

8. ANALYTE – What do you want to
detect?
BIOLOGICAL ELEMENT –It is the
sensitive biological element or
biological material (tissue,
microorganism, organelles, cell
receptor, enzymes, antibodies,
nucleic acids, etc.) that interacts
(binds or recognises) the analyte
under study.

9. TRANSDUCER-The transducer or the detector element transforms the signal
resulting from the interaction of the analyte with the biological recognition element
into another signal that can be more easily measured and quantified.
AMPLIFIER, MICROPROCESSOR, DISPLAY- Biosensor reader device with the
associated electronics or signal processors that are primarily responsible for the
display of the result .

10. Biosensor is broadly classified into two classes:
1. On the basis of biological element
a) Enzyme biosensor
b) Microbial biosensor
c) Antibody biosensor
2. On the basis of transducing element
a) Calorimetric/Thermal Detection Biosensor
b) Optical Biosensor
c) Resonant Biosensor
d) Piezoelectric Biosensor
e) Ion Sensitive Biosensor
f) Electrochemical Biosensor

11. Calorimetric/Thermal Detection Biosensor
• It consists of a heat insulated box fitted with heat
exchanger (aluminium cylinder). The reaction takes place
in a small enzyme packed bed reactor. As the substrate
enters the bed, it gets converted to a product and heat is
generated.
• The difference in the temperature between the substrate
and product is measured by thermistors. Even a small
change in the temperature can be detected by thermal
biosensors.
Optical Biosensor
• Optical biosensors are the devices that utilize the principle
of optical measurements (absorbance, fluorescence,
chemiluminescence etc.).
• Optical biosensors primarily involve enzymes an
antibodies as the transducing elements.

12. Piezoelectric biosensors
• Piezoelectric biosensors are based on the principle of acoustics (sound
vibrations), hence they are also called as acoustic biosensors. Piezoelectric
crystals form the basis of these biosensors. The crystals with positive and
negative charges vibrate with characteristic frequencies. Adsorption of certain
molecules on the crystal surface alters the resonance frequencies which can be
measured by electronic devices.
Electrochemical biosensors
• Generally, electrochemical biosensor works on the principle that many enzyme
catalysis reactions consumes or generates ions or electrons causing some change
in electrical properties of the solution which can be detected and used as a
measuring parameter.
• An electrochemical biosensor uses an electrochemical cell with electrodes of
different dimension and modifications.
• Three kinds of electrodes are generally used-
• Working electrode
• Reference electrode
• Counter or Auxilary electrode
• It is the working electrode where reaction occurs between electrode substrate
and analyte.

13. • Types of electrochemical biosensors
Electrochemical biosensors are classified into three types:
• Amperometric Biosensors
• Potentiometric Biosensors
• Conductimetric Biosensors
1. Amperometric Biosensors:
• These biosensors are based on the movement of electrons (i.e. determination of
electric current) as a result of enzyme-catalysed redox reactions. Normally, a
constant voltage passes between the electrodes which can be determined. In an
enzymatic reaction that occurs, the substrate or product can transfer an
electron with the electrode surface to be oxidised or reduced .This results in an
altered current flow that can be measured.
2. Potentiometric biosensors:
• Potentiometric biosensors use the ion-selective electrodes to convert the
biological reaction to electronic response.
• Most commonly used electrodes are pH meter glass electrodes (for cations
glass pH electrodes coated with a gas selective membrane for CO2, NH or
H2S.) or solid state electrodes.
• Biosensors detects and measures the ions or electrons generated in many
reactions, very weak buffer solutions are used in this case.
• Gas sensing electrodes detect and measure the amount of gas produced.

14. 3. Conductimetric biosensors:
• These biosensors measure electrical conductance/ resistance of the solution.
• Conductance measurement have comparatively low sensitivity.
4. Whole cell biosensors
• Whole cell biosensors are particularly useful for multi-step or cofactor requiring
reactions. These biosensors may employ live or dead microbial cells.

15. The advantages of biosensors include low cost, small size, quick and easy use,
as well as a sensitivity and selectivity greater than the current instruments.
Biosensors have many uses in clinical analysis, general health care monitoring. The
most popular example is glucose oxidase-based sensor used by individuals
suffering from diabetes to monitor glucose levels in blood. Biosensors have
found potential applications in the industrial processing and monitoring,
environmental pollution control, also in agricultural and food industries. The
introduction of suitable biosensors would have considerable impact in the following
areas:
A. Clinical and Diagnostic Applications:
1) Among wide range of applications of biosensors, the most important application
is in the field of medical diagnostics. The electrochemical variety is used now in
clinical biochemistry laboratories for measuring glucose and lactic acid.
2) Consumer self-testing, especially self-monitoring of blood components is another
important area of clinical medicine and healthcare to be impacted by commercial
biosensors.
3) Such testing will improve the efficiency of patient care, replacing the often slow
and labour intensive present tests. It will bring clinical medicine closer to bedside,
facilitating rapid clinical decision-making.

16. B. Industrial Applications:
1) Along with conventional industrial fermentation producing materials, many new
products are being produced by large-scale bacterial and eukaryotes cell culture.
2) The monitoring of these delicate and expensive processes is essential for
minimizing the costs of production; specific biosensors can be designed to
measure the generation of a fermentation product.
C. Environmental Monitoring:
1) Environmental water monitoring is an area in which whole cell biosensors may
have substantial advantages for combating the increasing number of pollutants
finding their way into the groundwater systems and hence into drinking water.
2) Important targets for pollution biosensors now include anionic pollutants such as
nitrates and phosphates. The area of biosensor development is of great
importance to military and defence applications such as detection of chemical and
biological species used in weapons.
D. Agricultural Industry:
1) Selective and sensitive microbial sensors for measurement of ammonia and
methane have been studied.
2) However, the only commercially available biosensors for wastewater quality
control are biological oxygen demand (BOD) analysers based on micro-organisms
like the bacteria Rhodococcus erythropolis immobilized in collagen or
polyacrylamide.