Micro Electro Mechanical Systems (MEMS)

1. Department of Instrumentation & Control Engineering, MIT, Manipal
Lecture #04
Micro Bio Sensors
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2. Department of Instrumentation & Control Engineering, MIT, Manipal
Contents
1. Introduction
2. Basic components of Biosensor
3. Working of Biosensor
4. Types of Biosensor
5. Applications of Biosensor
6. Nano-technological Approach
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3. Introduction
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Biosensors:
Self-contained integrated device that is capable of providing
specific qualitative or semi-quantitative analytical information
using a biological recognition element which is in direct-
spatial contact with a transduction element. (IUPAC,1998).
A sensor that integrates a biological element with a
physiochemical transducer to produce an electronic signal
proportional to a single analyte which is then conveyed to a
detector.
Biosensors are analytical tools for the analysis of bio-material
samples to gain an understanding of their bio-composition,
structure and function by converting a biological response into
a measurable response.
S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

4. Introduction
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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
an 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.
S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

5. Introduction
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Analyte - Protein, toxin, peptide, vitamin, sugar, metal ion
Delivery - (Micro) fluidics, Concentration (increase /
decrease), Filtration / selection
S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

6. Introduction
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Analyte diffuses from the solution to the surface of the Biosensor.
Analyte reacts specifically & 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/electronic properties of the
Transducer Surface.
The change in the optical/electronic properties is measured /
converted into electrical signal, which is detected.
S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

7. Introduction
7S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

8. Bio-sensor:
It is a typically complex chemical system usually extracted
or derived directly from a biological organism.
Types :
Enzymes - Antibodies
Oxidase - Tissue
Polysaccharide - Nucleic Acid
Basic Components
8S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

9. Bio-element:
Function: To convert biological response in to an
electrical signal.
Types :
Electrochemical
Optical
Piezoelectric
Transducers
9S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

10. Schematic Diagram of a Biosensor
Working of Biosensors
10S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

11. Schematic Diagram of a Biosensor
Working of Biosensors
11S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

12. • 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.
Response from Bio-Element
12S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

13. Electrochemical biosensor
Optical biosensor
Thermal biosensor
Resonant biosensor
Ion-sensitive biosensor
Types of Biosensors
13S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

14. Types of Biosensors
14S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

15. 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
15S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

16. This 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 parameter is current.
Amperometric Biosensors
16S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

17. • 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 helps in minimizing undesirable effects such as
Faradaic processes, double layer charging and concentration
polarization.
Conductometric Biosensors
17S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

18. • 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 when a ramp
voltage is applied to an electrode in solution, a current flow
occurs because of electrochemical reactions.
• The voltage at which these reactions occur indicates a
particular reaction and particular species.
Potentiometric Biosensors
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19. Electrochemical Sensing Characteristics
19S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

20. • 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 Biosensors
20S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

21. • 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 enzyme
molecules with temperature sensors. When the analyte comes
in contact with the enzyme, the heat reaction of 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.
Thermal Detection Biosensors
21S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

22. • 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 thermistors 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 biosensor include the
detection of pesticides and pathogenic bacteria.
Thermal Detection Biosensors
22S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

23. • It Utilize crystals which undergo an elastic 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).
• When the analyte molecule (or antigen) gets attached to the
membrane, the mass of the membrane changes. The resulting
change in the mass subsequently changes the resonant
frequency of the transducer. This frequency change is then
measured.
Resonant Biosensors
23S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

24. • These are semiconductor FETs having an ion-sensitive
surface.
• The surface electrical potential changes when the ions and the
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 turn
cause a change in the FET surface potential.
• This type of biosensor is also called an ENFET (Enzyme
Field Effect Transistor) and is primarily used for pH
detection.
Ion Sensitive Biosensors
24S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

25. • Glucose reacts with glucose
oxidase (GOD) to form gluconic
acid. Two electrons & two
protons are also produced.
• Glucose mediator reacts with
surrounding oxygen to form H2O2
and GOD.
• Now this GOD can reacts with
more glucose.
• Higher the glucose content,
higher the oxygen consumption.
• Glucose content can be detected
by Pt-electrode
Glucose Biosensors
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26. Transducers Comparison
26S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

27. In food industry, biosensors are used to monitor the freshness of food.
Drug discovery and evaluation of biological activity of new compounds.
Potentiometric biosensors are intended primarily for monitoring levels
of carbon dioxide, ammonia, and other gases dissolved in blood and
other liquids.
Environmental applications e.g. the detection of pesticides and river
water contaminants.
Determination of drug residues in food, such as antibiotics and growth
promoters.
Glucose monitoring in diabetes patients.
Analytical measurement of folic acid, biotin, vitamin B12 and
pantothenic acid.
Enzyme-based biosensors are used for continuous monitoring of
compounds such as methanol, acetonitrile, phenolics in process streams,
effluents and groundwater.
Applications of Biosensors
27S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal

28. Nano-technological Approaches
28S.Meenatchisundaram, Department of Instrumentation & Control Engineering, MIT, Manipal