This document discusses biosensors, which are analytical devices that convert biological reactions into electrical signals. It outlines different types of biosensors including amperometric, potentiometric, conductometric, optical, piezoelectric, whole cell, and immunobiosensors. Applications of biosensors include food analysis, medical diagnosis, environmental monitoring, and industrial process control. The document concludes that biosensors have potential but are still evolving from research prototypes to commercial products.
3. INTRODUCTION
Biosensors are analytical devices that converts biological actions into
electrical signals in order to quantify them. They Make use of the
specificity of biological process: enzymes for their substrates or other
legands, antibodies for their antigens,lactins for carbohydrates and nuclic
acids for their complementary sequences or antibodies.
In 1987, for the first time yellow springs instruments co.USA developed
a biosensor for Diagnostic purposes, for measuring glucose in blood
plasma. It is a hand-held machine which measures 6 components of
blood plasma such as glucose,urea,nitrogen,sodium,Potassium and
chloride.
An indigenous glucose sensor has been developed by the scientists at
Central electro chemical research Institute (CECRI)Karaikudi.it gives
electrical signals for a glucose concentration as low as 0-15mM.
4. Schematic outline of biosensor
A biosensor is an analytical device consisting of an immobilized layer of
biological material (eg enzyme,antibody,organell,harmones,nucleic acids
or whole cell) in the intimate contact with a transducer that is a sensor
which analysis the biological signals and convert into an electrical
signal.
The substance to be measured pass through the membrane and interact
with the immobilized material and yield product.
The product passes through another membrane to the transducer.
The transducer converts the product into an electrical signals which is
amplified.
The signal processing equipment converts the amplified signals into a
display read out.
6. Amperometric biosensor
These biosensors are based on the movement of electrons (ie,
determination of electric current) as a result of enzyme catalyzed redox
reactions. Normally, a constant voltage passes between the electrodes
which can be determined. In the 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
7. Potentiometric biosensor
In these biosensors, changes in ionic concentrations are determined by
use of Ion selective electrodes. pH electrode is the most commonly used
Ion selective electrode, since many enzymatic reactions involve the
release or absorption of hydrogen ions. The Other important electrodes
are Ammonia selective and co2 selective electrodes.
The potential difference obtained between the potentiometric electrode
and the reference electrode can be measured. Ion selective field effect
transistors (ISFET) biosensor is a good example used to monitor
intramyocardial pH during open heart surgery
8. Conductometric biosensor
Many biological processes involve changes in the concentrations of ionic
species. Such changes can be utilised by biosensors that detect changes
in electrical conductivity. A typical example of such biosensor is the urea
sensor, utilising immobilized urease, and used as a monitor during renal
surgery and dialysis.
An alternating field between the two electrodes allows the conductivity
changes to be determined. The electrodes are interdigitated to give a
relatively long track length within a small sensing area. A steady state
response can be achieved in a few seconds allowing urea to be
determined in the range 0.1 to 10 mm
9. Optical biosensor
The optical biosensor is a device, that utilizes the principle of optical
measurements like fluorescence, absorbance etc.. they used in fibre
optics and optoelectronic transducers.The optical biosensors are safe for
non Electrical remote sensing of materials in the transducer elements
primarily optical biosensors involves in the enzymes and antibodies.
Usually these bus answers is not required a reference sensors and the
comparative signals are generated by using the sampling sensor
A simple example of this is fibre optic lactate sensor which senses
changes in molecular oxygen concentrations by determining its
quenching of a fluorescent dye.
10. Piezoelectric biosensor
The piezoelectric effect is due to some crystals containing positive and
negative charges that separates when the Crystal is subjected to a stress,
causing the establishment of an electric field. As a consequence, as this
crystal is subjected to an electric field of resonant frequency will cause
The Crystal to vibrate with the characteristic frequency dependent on its
composition and it's thickness as well as the way it has been cut. As this
resonant frequency varies when molecules absorb to the Crystal surface,
a piezoelectric crystal may form the basis of a biosensor
11. Whole cell biosensor
As biocatalysts whole microbial cells can offer some advantages over
pure enzymes when used in biosensors. Generally microbial cells are
cheaper have longer active life time and are less sensitive to inhibition,
pH and temperature variations than the isolated enzyme. Against these
advantages, such devices usually offer longer response and recovery
times and lower selectivity.they are particularly useful Where multi-step
or coenzyme requiring reactions are necessary. The microbial cells maybe
viable or dead.the advantage of using viable cells is that the sensor may
posses a self repairing capability.
Biochemical oxygen demand biosensors often use a single selected
microbial spaces.
12. Immuno biosensors
Immunosensors work on the principle of immunological specificity,
coupled with measurement based on amperometric or potentiometric
biosensors.there are several possible configuration for immuno
biosensors some of them or
A. An immobilized antibody to which antigen can bind directly.
B. An immobilized antigen that binds to antibody which in turn can bind
to a free second antigen.
C. An antibody bound to immobilized antigen which can be partially
released by competing with free antigen.
D. An immobilized antibody binding free antigen an enzyme labelled
antigen in competition.
For the biosensors A B and C piezoelectric devices can be used. The
immuno biosensors using enzymes are most commonly employee
amperometric or thermometric devices.
13.
14. Applications of biosensors
In recent years these sensors have been become very popular and they
are applicable in different fields some of them are mentioned below
1. Food analysis
2. Study of biomolecules and their interactions
3. Drug development
4. Crime detection
5. Medical diagnosis
6. Environmental field monitoring
7. Industrial process control
8. Manufacturing of pharmaceuticals and replacement of organs
15. Summary
A biosensor is an analytical device used for the detection of a
chemical substance, that combines a biological component with a
physico-chemical detector. Biosensors can be grouped according
to their biological element or the transduction elements. There are
many potential applications of biosensors of various types,the
main requirement for a biosensor approach to be valuable in
terms of research and commercial applications are the
identification of target molecule.
16. Conclusion
Biosensors form an interesting and varied part of biotechnology.
They have been applied to solve a number of analytical
problems and some have achieved notable commercial success.
They have been slow to evolve from research prototype to the
market and have not yet reached their full potential. Many more
commercial products are expected over the next few years,
particularly in medical diagnosis.
17. References
• Waalker.J.M And Rapley.R (2002) Molecular biology and
Biotechnology IVth edn.Panima Publishing Corporation.New Delhi
Pp555
• Dubey.R.C(1993) A Text of Biotechnology.S.Chand And Company
LTD.NewDelhi Pp702
• Elyn.d(2014) Biotechnolog.Scintific International PVT LTD.New
Delhi.Pp440
