PREVIOUS WORK DONE
WORKING OF E-NOSE
E-NOSE VS. BIO NOSE
An electronic nose is a
device that identifies the
specific components of an
odor and analyzes its
chemical makeup to find it.
It consists of certain
mechanisms such as an
array of electronic sensors
for chemical detection and
artificial neural network for
E-nose was first suggested by K. Persaud and
George Dodd of Warwick University in 1982.
Then afterwards in 1988, another professor of this
university named Julian Gardner conducted his
research on this.
It then came into popular use after 1989.
Since then, development of sensor array-based
instruments has been actively pursued in Asia, Europe
and North America.
The electronic nose was
developed in order to mimic
the human olfaction.
Essentially, e-nose consists of
three major parts:
• Sample Delivery System
• Detection System
• Computing system
•The sample delivery system enables the delivery
of sample( volatile compounds).
• The detection system, which consists of a
sensor set, is the “reactive” part of the
instrument. When in contact with volatile
compounds, the sensors experience a change of
electrical properties. Each sensor is sensitive to all
volatile molecules but each in their specific way.
•The computing system works to combine the
responses of all the sensors which represent the
input for the data treatment; it then performs
analysis and provides results.
•In a typical e-nose, an air sample is pulled by a vacuum
pump through a tube into a small chamber housing the
electronic sensor array.
•A sample-handling unit exposes the sensors to the
odorant, producing a response as the VOCs interact with
the active material.
•The sensor response is recorded and delivered to the
•Then a washing gas such as alcohol is applied to the
array for a few seconds or a minute, so as to remove the
odorant mixture from the active material.
Based on the type of sensors employed, e-nose can
be classified into the following categories:
• Conductivity Sensors
• Polymer Sensors
• Piezoelectric Sensors
• FET Gas Sensors
• Optical Sensors
CONDUCTIVITY SENSORS:These types of sensors exhibit a change in
conductance when exposed to volatile organic
POLYMER SENSORS :-
Here the active material is a conducting polymer from
such families as the Polypyrroles, thiophenes, indoles
or furans. Changes in the conductivity of these
materials occur as they are exposed to various types of
chemicals, as certain reactions take place.
All of the polymer films on a set of electrodes
(sensors) start out at a measured resistance, their
baseline resistance. If there has been no change in
the composition of the air, the films stay at the
baseline resistance and the percent change is zero.
Each polymer changes its size, and therefore its
resistance, by a different amount, making a pattern of
If a different compound had caused the polymer to
change, the pattern of the polymer films' change
would have been different.
A piezoelectric sensor is a device that uses the
piezoelectric effect to measure any physical change like
pressure, strain etc. Here, the gas adsorption leads to
change in mass of the sensor .
FET GAS SENSORS:Chemical FET(Field-effect transistor) is a type of a fieldeffect transistor acting as a chemical sensor. In this, the
charge on the gate electrode is applied by a chemical
process which may be used to detect atoms, molecules,
and ions in liquids and gases .
OPTICAL SENSORS:•These utilize glass fibers with a chemically active
material coating on their sides or ends.
•A light source is used to interrogate the active
material which responds with the change in color
to the presence of VOCs.
•The active material contains chemically active
fluorescent dyes. As the VOCs interact with it, the
color of the fluorescent dye changes, hence lead
1. It uses the lungs to bring the
odor to epithelium layer.
1. It employs a pump to
smell the odor.
2. It has mucus, membrane and
hair to act as filter.
2. It has an inlet sampling
system that provides
The human nose contains 3. E-nose has a variety of
sensors that interact
which contains millions of
differently with the
sensing cells that interact with
the odorous molecules in
The human receptors
responses to electronic
nerve impulses whose
propagated by neurons
through a complex network
before reaching the higher
brain for interpretation.
4. Similarly, the chemical
sensors in the E-nose react
with the sample and produce
electrical signals. A computer
reads the unique pattern of
signals, and interprets them
with some form of intelligent
•The Cyranose 320 is a
Pasadena, California in
using the Cyranose 320
includes the detection of
COPD, and other medical
conditions as well as
In environmental monitoring:
• For identification of volatile organic compounds in
air, water and soil samples.
•For environmental protection.
In quality control laboratories:
• Conformity of raw material, intermediate
• Detection of contamination, spoilage and
• Monitoring of storage conditions.
For medical diagnosis:As the sense of smell is an important sense to the
physician, an e-nose has applicability as a diagnostic
tool. It can examine odors from the body and thus can
identify possible problems.
In food industry:Currently, this is the biggest market for e-nose. Its
applications include quality assessment in food
production and monitoring various food items based on
The human sniffers are costly as compared to
e-nose. Also detection of hazardous gases by them
is not possible.
E-nose has wide range of sensitivity.
Results obtained by e-nose are fast and more
It is well- suited for repetitive or boring tasks.
It can also detect substances which are not
detected by our human nose, like mercury.
E-nose can only identify a standard set of odors
which is stored in its database.
Though it is effective but still it can’t mimic the
complex human olfactory system exactly.
They also have shorter lifetime because of the
sensors employed in them.
Moreover, e-noses available in market are not
In the field of health and security:
• The quality control of food products as it could be
conveniently placed in food packaging to clearly
indicate when food has started to rot.
• It is used to detect bacterial contamination in the
• It can be used to detect the cancers like brain and
• A more futuristic application of e-nose has been
recently proposed for telesurgery.
In the field of crime prevention:• The ability of the electronic nose to detect odorless
chemicals makes it ideal for use in the police
force, such as to detect drug odors despite other
airborne odors capable of confusing police dogs.
However this is unlikely in the mean time as the cost
of the electronic nose is too great and until its price
drops significantly it is unlikely to happen.
•It may also be used as a bomb detection method in
airports. Through careful placement of several or more
electronic noses and effective computer systems you
could triangulate the location of bombs to within a few
meters of their location in less than a few seconds
An electronic nose is a system created to mimic the
functioning of human nose.
Since the whole working is automatic, it can also be
used by non specialists.
Although it has several advantages, yet it is still far
from the selectivity provided by a human nose.
Basically, it is a tool provided to overcome the
shortcomings of human nose thus giving us more fast
and accurate results.
Future developments in the use of advanced sensor
arrays and the development of adaptive artificial neural
networking techniques will lead to superior electronic
H. V. Shurmur, “The fifth sense: on the scent
of the electronic nose” IEEE Review, pp:- 5998, March 1990