BME-5107

Biosensors and Bioelectronics

Course Objectives:

This course helps to understand the working principles

of various Bio-sensing equipment.
 Sensor, Biosensor, and Bioelectronics
A sensor is a device that detects the change in the environment and responds to some
output on the other system. A sensor converts a physical phenomenon into a measurable
analog voltage (or sometimes a digital signal) converted into a human-readable display or
transmitted for reading or further processing.

A Biosensor is a device that measures biological or chemical reactions by generating

signals proportional to the concentration of an analyte in the reaction.

Bioelectronics is a multidisciplinary field which integrates biology and electronics

for diagnostic and therapeutic healthcare treatments. The regulatory activities of the
nervous system can be monitored and controlled with bioelectronic technologies that
affect specific molecular processes in neural signaling.

Chapter-One and Two

Introduction and Transducers
 Outline:
Definition
Introduction
Types
Principle

Definition
• A biosensor is an analytical device, used for
the detection of an analyte, that combines a
biological component with a physicochemical
detector.
Biosensor system
 Introduction
• A biosensor is a sensing device comprised of a
combination of a specific biological element and a
transducer.
• A specific biological element recognizes a specific
analyte and the changes in the biomolecule are
usually converted into and electrical signal ( which
is in turn calibrated to a specific scale ) by a
transducer.
• It detects, records and transmits information
regarding a physiological change or process.

A successful biosensor must possess at least

some of the following beneficial features:
• The biocatalyst must be highly specific for the purpose
of the analyses, be stable under normal storage
conditions and, except in the case of colorimetric
enzyme strips
• The reaction should be as independent of such physical
parameters as stirring, pH and temperature as is
manageable. This would allow the analysis of samples
with minimal pre-treatment.
• The response should be accurate, precise, reproducible
and linear over the useful analytical range, without
dilution or concentration. It should also be free from
electrical noise.
• If the biosensor is to be used for invasive monitoring in
clinical situations, the probe must be tiny and
biocompatible, having no toxic or antigenic effects. If it
is to be used in fermenters it should be serializable.
This is preferably performed by autoclaving, but no
biosensor enzymes can presently withstand such drastic
wet-heat treatment. In either case, the biosensor should
not be prone to fouling or proteolysis.
• The complete biosensor should be cheap, small,
portable and capable of being used by semi-skilled
operators.

Glucometer
• Current glucometers use test strips containing
glucose oxidase, an enzyme that reacts to
glucose in the blood droplet,
• When the strip is inserted into the meter, the
flux of the glucose reaction generates an
electrical signal
• The glucometer is calibrated so the number
appearing in its digital readout corresponds to
the strength of the electrical current
 Bio-element
• It is a typically complex chemical system usually
extracted or derived directly from a biological
organism.
• Types
• Enzymes
• Oxidase
• Polysaccharide
• Antibiotics
• Tissue
• Nucleic acid

Conti…
• Function
• To interact specifically with a target compound
i.e compound to be detected.
• It must be capable of detecting the presence of
a target compound in the test solution.
• The ability of a bio-element to interact
specifically with the target compound
(specifically) is the basis for biosensor.
 Transducer
• Function
• To convert biological response in to an
electrical signal.
• Types
• Electrochemical
• Optical
• Piezoelectric

Response From Bio-element

• Heat absorbed (or liberated) during the
interaction.
• Movement of electrons produced in a redox
reaction.
• Light absorbed ( or liberated ) during the
interaction.
• Effect due to mass of reactants or products.
 Types Of Biosensors

• Electrochemical biosensor
• Optical biosensor
• Thermal biosensor
• Resonant biosensor
• Ion-sensitive biosensor

Classification of Biosensors:
Characteristics of a Biosensor Classification based on transducer system
❖ Calorimetric (detect on the basis of heat evolved in biological
reaction)
❖ Piezoelectric (detect on the basis of electric dipoles generated due
to mechanical stress)
❖ Optical(detect on the basis of change in light recepived )
❖ Electrochemical such as Potentiometric, Conductometric and
Amperometric
 Classification based on bio-recognition element:
Enzyme
DNA
Antigen-antibody
Cell

Characteristics of a Biosensor
(i) Selectivity, (ii) Recovery time (iii) Shelf-life (iv)Stability,
(v) Response time, (vi) Accuracy, (vii)Reusability

Biocatalysis based Biosensors

Bio-affinity based Biosensors
Microorganisms Based Biosensors

Biocatalysis based biosensors are dependent on Enzymes.

Two mechanisms used in the Biocatalysis based biosensors are:

•Mechanism in which the enzyme catalytically transforms the

analyte
•Mechanism in which the analyte inhibits the activity of the
enzyme.
 The Bio-affinity sensor produces high sensitivity by
employing enzyme amplification techniques. The
sensitivity of such a biosensor is dependent on the
turnover number of the enzyme and the method
employed to detect the product of the catalyzed
reaction.

A microbial biosensor is an analytical device which

integrates microorganism(s) with a physical
transducer to generate a measurable signal
proportional to the concentration of analytes.

Though there are countless ways to make a whole-cell

microbial biosensor, the basic principle is the same: a
bacterial cell is programmed (usually via genetic
engineering) to recognize and generate a measurable
signal in response to a molecule of interest.
Biological specimens (or biospecimens), such
as blood, urine, saliva, and many other types, are
collected for a variety of reasons, for normal patient
monitoring and care as well as for basic, clinical and
epidemiologic research studies.

An analyte, component (in clinical chemistry),

titrant (in titrations), or chemical species is a
substance or chemical constituent that is of interest
in an analytical procedure.
•Advantages:
Specificity
•Fast reaction time and thus a fast response time is
observed
•Disadvantages:
Expensive
•Lose activity when the operational conditions are beyond
limits (pH, Temp etc.)
•Lose activity after few cycles of use
 Chapter- Two
Transducers in Biosensors

Transducer
• Function
• To convert biological response in to an
electrical signal.
• Types
• Electrochemical
• Optical
• Piezoelectric
 Electrochemical biosensor
• 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 Biosensors
2. Conductimetric Biosensors
3. Potentiometric Biosensors
 Electrochemical biosensor

Amperometry Biosensors
• The high sensitivity biosensor can detect
electro-active species present in biological test
samples.
• Since the biological test samples may not be
intrinsically electro-active, enzymes are
needed to catalyze the production of
radio-active species.
• In this case, the measured parameters is
current.
 Conductimetric Biosensors
• The measured parameter is the electrical
conductance resistance of the solution.
• When electrochemical reactions produce ions or
electrons, the overall conductivity or resistivity of
the solution changes. This change is measured and
calibrated to a proper scale (Conductance
measurements have relatively low sensitivity).
• The electric field is generated using a sinusoidal
voltage (AC) which in minimizing undesirable
effects such as Faradaic process, double layer
charging and concentration polarization.

Conductimetric biosensor
 Potentiometric biosensors
• In this type of sensor the measured parameter is
oxidation or reduction potential of an
electrochemical reaction.
• The working principle relies on the fact that where
a ramp voltage is applied to an electrode in
solution, a current flow occurs because of
electrochemical reactions.
• The voltage at which these reaction occurs indicate
a particular reaction and particular species.

Potentiometric biosensor
 Optical detection biosensor
• The output transduced signal that is measured is light
for this type of biosensor.
• The biosensor can be made based on optical
diffraction. In optical diffraction-based devices, a
silicon wafer is coated with a protein via covalent
bonds. The wafer is exposed to UV light through a
photo-mask and the antibodies become inactive in the
exposed regions. When the diced wafer chips are
incubated in an analyte, antigen-antibody bindings are
formed in the active regions , thus creating a diffraction
grating. This grating produces a diffraction signal when
illuminated with a light source such as laser. The
resulting signal can be measured.

Optical detection biosensor

 Thermal detection biosensors
• This type of biosensor work on the fundamental properties
of biological reactions, namely absorption or production of
heat , which in turn changes the temperature of the medium
in which the reaction takes place.
• They are constructed by combining immobilized enzymes
molecules with the temperature sensors. When the analyte
comes in contact with the enzyme is measured and is
calibrated against the analyte concentration.
• The total heat produced or absorbed is proportional to the
molar enthalpy and the total number of molecules in the
reaction.

Conti…
• The measurement of the temperature is typically
accomplished via a thermistor, and such devices are
known as enzyme thermistors. Their high sensitivity to
thermal changes makes thermistor ideal for such
applications.
• Unlike other transducers, thermal biosensors do not
need frequent recalibration and are insensitive to the
optical and electrochemical properties of the sample.
• Common applications of this type of biosensors
includes the detection of pesticides and pathogenic
bacteria.
 Thermal detection biosensors

Resonant biosensors
• It utilize crystal which undergo an electric
deformation when an electrical potential is
applied to them. (Alternating potential (A.C)
produces a standing wave in the crystal at a
characteristic frequency)
• In this type of biosensor, an acoustic wave
transducer is coupled with an antibody
(bio-element).
 Conti…
• When the analyte molecule (or antigen) gets
attached to the membrane, the mass of the
membrane, the mass of the membrane changes.
The resulting change in the mass subsequently
changes the resonant frequency of the resonant
frequency of the transducer. This frequency
change is then measured.

Resonant biosensors
 Ion sensitive biosensor
• These are semiconductor FETs having an ion-sensitive
surface.
• The surface electrical potential changes when the ions
and semiconductor interact. (This change in the
potential can be subsequently measured).
• The Ion sensitive Field Effect Transistor (ISFET) can
be constructed by covering the sensor electrode with a
polymer layer. This polymer layer is selectively
permeable to analyte ions. The ions diffuse through the
polymer layer and in return cause a change in the FET
surface potential.

Conti…
• This type of biosensor is also called an ENFET
(Enzyme Field Effect Transistor) and is
primarily used for pH detection.
 Ion sensitive biosensors

Glucose biosensors
• Glucose reacts with glucose oxidase to form
gluconic acid. Two electrons and two protons are
also produced.
• Glucose mediator reacts with surrounding oxygen
to form H2O2 and glucose oxidase.
• Now this glucose oxidase react with more glucose.
• Higher the glucose content, the higher the oxygen
consumption.
• Glucose content can be detected by Pt-electrode.
Glucose biosensors

Applications
 Conclusion
• As the potential threat to bioterrorism increase,
there is great need for a tool that can quickly,
reliably and accurately detect contaminating
bio-agents in the atmosphere.
• Biosensors can essentially serve as low-cost and
highly efficient devices for this purpose in addition
to being used in other day-to-day application.
• Biosensors are known as immuno-sensors,
optrodes, chemical, canaries, resonant mirrors,
glucometers biochips bio-computers and so on.