The term “biosensor” is short for “biological sensor.

” The device is made up of a

transducer and a biological element that may be an enzyme, an antibody or a nucleic
acid. The bioelement interacts with the analyte being tested and the biological response
is converted into an electrical signal by the transducer. Depending on their particular
application, biosensors are also known as immunosensors, optrodes, resonant mirrors,
chemical canaries, biochips, glucometers and biocomputers. A commonly cited
definition of a biosensor is:

“A chemical sensing device in which a biologically derived recognition is coupled to a

transducer, to allow the quantitative development of some complex biochemical
parameter.”

Parts of a biosensor

Every biosensor comprises:

 A biological component that acts as the sensor

 An electronic component that detects and transmits the signal

Biosensor elements

A variety of substances may be used as the bioelement in a biosensor. Examples of

these include:

 Nucleic acids
 Proteins including enzymes and antibodies. Antibody-based biosensors are also
called immunosensors.
 Plant proteins or lectins
 Complex materials like tissue slices, microorganisms and organelles

The signal generated when the sensor interacts with the analyte may be electrical,
optical or thermal. It is then converted by means of a suitable transducer into a
measurable electrical parameter – usually a current or voltage.
Working principle of biosensor

Applications
Biosensor probes are becoming increasingly sophisticated, mainly owing to a
combination of advances in two technological fields: microelectronics and
biotechnology. Biosensors are highly valuable devices for measuring a wide spectrum
of analytes including organic compounds, gases, ions and bacteria.

History of biosensor

The first experiment to mark the origin of biosensors was carried out by Leland C.
Clark. For his experiment, Clark used platinum (Pt) electrodes to detect oxygen.
He placed the enzyme glucose oxidase (GOD) very close to the surface of
platinum by trapping it against the electrodes with a piece of dialysis membrane.
The enzyme activity was modified according to the surrounding oxygen
concentration. Glucose reacts with glucose oxidase (GOD) to give gluconic acid
and produces two electrons and two protons, thereby reducing GOD. The
reduced GOD, the electrons, protons and the surrounding oxygen all react to give
hydrogen peroxide and oxidized GOD (the original form), therefore making more
GOD available for more glucose to react with. The higher the glucose content, the
more oxygen is consumed and the lower the glucose content, the more hydrogen
peroxide is produced. This means either an increase in hydrogen peroxide or a
decrease in oxygen can be measured to give an indication of the glucose
concentration.

Applications of Biosensors
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This article throws light upon the four applications of

biosensors. The four applications are: (1) Applications in
Medicine and Health (2) Applications in Industry (3)
Applications in Pollution Control and (4) Applications in
Military.
Biosensors have become very popular in recent years. They are widely
used in various fields. Biosensors are small in size and can be easily
handled. They are specific and sensitive, and work in a cost-effective
manner. The tentative market share of biosensor applications is given
in Table 21.9. Some of the important applications of biosensors are
broadly described hereunder.
1. Applications in Medicine and Health:
Biosensors are successfully used for the quantitative estimation of
several biologically important substances in body fluids e.g. glucose,
cholesterol, urea. Glucose biosensor is a boon for diabetic patients for
regular monitoring of blood glucose. Blood gas monitoring for pH,
pCO2 and pO2 is carried out during critical care and surgical
monitoring of patients. Mutagenicity of several chemicals can be
determined by using biosensors. Several toxic compounds produced in
the body can also be detected.
2. Applications in Industry:
Biosensors can be used for monitoring of fermentation products and
estimation of various ions. Thus, biosensors help for improving the
fermentation conditions for a better yield. Now a days, biosensors are
employed to measure the odour and freshness of foods. For instance,
freshness of stored fish can be detected by ATPase. ATP is not found in
spoiled fish and this can be detected by using ATPase. One
pharmaceutical company has developed immobilized cholesterol
oxidase system for measurement of cholesterol concentration in foods
(e.g. butter).

3. Applications in Pollution Control:

Biosensors are very helpful to monitor environmental (air, water)
pollution. The concentrations of pesticides and the biological oxygen
demand (BOD) can be measured by biosensors. Several environmental
pollutants can be evaluated for their mutagenicity by employing
biosensors.
4. Applications in Military:
Biosensors have been developed to detect the toxic gases and other
chemical agents used during war.

Wearable sensors
Wearable sensors and systems have evolved to the point that they can be considered ready for
clinical application. The use of wearable monitoring devices that allow continuous or intermittent
monitoring of physiological signals is critical for the advancement of both the diagnosis as well as
treatment of diseases.

Wearable systems are totally non-obtrusive devices that allow physicians to overcome the limitations
of ambulatory technology and provide a response to the need for monitoring individuals over weeks
or months.
They typically rely on wireless miniature sensors enclosed in patches or bandages or in items that
can be worn, such as ring or shirt. The data sets recorded using these systems are then processed
to detect events predictive of possible worsening of the patient's clinical situations or they are
explored to access the impact of clinical interventions.
It is a pulse oximetry sensor that allows one to continuously monitor heart rate and oxygen
saturation in a totally unobtrusive way. The device is shaped like a ring and thus it can be worn for
long periods of time without any discomfort to the subject. The ring sensor is equipped with a low
power transceiver that accomplishes bi-directional communication with a base station, and to upload
date at any point in time.
Each time the heart muscle contracts,blood is ejected from the ventricles and a pulse of pressure is
transmitted through the circulatory system.This pressure pulse when traveling through the
vessels,causes vessel wall displacement which is measurable at various points.inorder to detect
pulsatile blood volume changes by photoelectric method,photo conductors are used.normally photo
resistors are used, for amplification purpose photo transistors are used.
Light is emitted by LED and transmitted through the artery and the resistance of photo resistor is
determined by the amount of light reaching it.with each contraction of heart,blood is forced to the
extremities and the amount of blood in the finger increases.it alters the optical density with the result
that the light transmission through the finger reduces and the resistance of the photo resistor
increases accordingly.
The photoresistor is connected as a part of voltage divider circuit and produces a voltage that varies
with the amount of blood in the finger.This voltage that closely follows the pressure pulse.

DEVELOPMENT OF WEARABLE BIOSENSOR

RING SENSOR
It is a pulse oximetry sensor that allows one to continuously monitor heart rate and oxygen
saturation in a totally unobtrusive way. The device is shaped like a ring and thus it can be worn for
long periods of time without any discomfort to the subject. The ring sensor is equipped with a low
power transceiver that accomplishes bi-directional communication with a base station, and to upload
date at any point in time.

BASIC PRINCIPLE OF RING SENSOR

Each time the heart muscle contracts, blood is ejected from the ventricles and a pulse of pressure is
transmitted through the circulatory system. This pressure pulse when traveling through the vessels,
causes vessel wall displacement which is measurable at various points inorder to detect pulsatile
blood volume changes by photoelectric method, photo conductors are used normally photo resistors
are used, for amplification purpose photo transistors are used.
Light is emitted by LED and transmitted through the artery and the resistance of photo resistor is
determined by the amount of light reaching it. with each contraction of heart, blood is forced to the
extremities and the amount of blood in the finger increases. It alters the optical density with the result
that the light transmission through the finger reduces and the resistance of the photo resistor
increases accordingly. The photoresistor is connected as a part of voltage divider circuit and
produces a voltage that varies with the amount of blood in the finger.This voltage that closely follows
the pressure pulse

WORKING
The LEDs and PD are placed on the flanks of the finger either reflective or transmittal type can be
used. For avoiding motion disturbances quite stable transmittal method is used. Transmittal type has
a powerful LED for transmitting light across the finger. This power consumption problem can be
solved with a light modulation technique using high-speed devices. Instead of lighting the skiing
continuously, the LED is turned ON only for a short time, say 10-100 ns, and the signal is sampled
within this period, high frequency, low duty rate modulation is used for preventing skin-burning
problem. The motion of the finger can be measure with an optical sensor. This motion detector can
be used not only for monitoring the presence of motion but also for cencelling the noise. By using
PD-B as a noise reference, a noise cencellation filter can be built to eliminate the noise of PD-A that
completes with the noise references used. And adaptive noise cancellation method is used.
The noise-canceling filter combines two sensor signals; one is the main signal captured by PD-A and
the other is the noise reference obtained by PD-B. The main signal mostly consists of the truce
pulsate signal, but it does contain some noise. If we know the proportion of noise contained in the
main signal, we can sensate the contained in the main signal, we can generate the noise of the
same magnitude by attending the noise reference signal and then subtract the noise from the main
signal to recover the true pulsatile signal.
The ring has a microcomputer performing all the device controls and low level signal processing
including LED modulation, data acquisition, filtering, and bi-directional RF communication. The
acquired waveforms sampled at 100Hz are transmitted to a cellular phone carried by the patient
through an RF link of 105Kbps at a carrier frequency of 915 MHz. The cellular phone accesses a
website for data storage and clinical diagnosis.