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Title: biosensor


1
BIOSENSORS
Prepared by Samaneh Rahamooz Haghighi PHD
student
may2015
2
BiosensorsSection 1
3
SENSOR
  • A small device used for direct measurement of a
    physical quantity of an analyte in a sample
    matrix
  • Response is continuous and reversible
  • Sample is not perturbed
  • Does not require sample collection and
    preparation
  • Consists of a transduction element covered by a
    recognition layer
  • Recognition layer may be chemical or biological
  • Recognition layer interacts with target analyte
  • Transduction element translates the chemical
    changes into electrical signals

4
History of Biosensors
  • First described in 1962 by Dr. Leland Clark
  • 1969 a sensor was invented to detect urea
  • 1972 the first glucose biosensor commercialized
    by Yellow Springs Instruments

Dr. Leland Clark Jr Father of the biosensor
5
1980s ---- Biosensors Would Solve the World's
Analytical Needs ? Industry -- process
monitoring and control, particularly food and
drink ? Medicine -- diagnostics, metabolites,
hormones ? Military -- battlefield monitoring of
poison gases, nerve agents people ? Domestic
-- home monitoring of non acute conditions
6
Introduction
  • Biosensors 3B
  • 90 ? Glucose testing
  • 8 - 10 increase in industry per year

7
Market Size of Biosensors
  • 7.3 Billion in 2003
  • 10.2 Billion in 2007 with a growth rate of about
    10.4

8
Biosensor Development
  • 1916 First report on the immobilization of
    proteins adsorption of invertase on activated
    charcoal.
  • 1956 Invention of the first oxygen electrode
    Leland Clark
  • 1962 First description of a biosensor an
    amperometric enzyme electrode for glucose.
    Leland Clark, New York Academy of Sciences
    Symposium
  • 1969 First potentiometric biosensor urease
    immobilized on an ammonia electrode to detect
    urea. Guilbault and Montalvo
  • 1970 Invention of the Ion-Selective Field-Effect
    Transistor (ISFET).

9
History of Biosensors
  • 1975 First commercial biosensor ( Yellow
    springs
  • Instruments
    glucose biosensor)
  • 1975 First microbe based biosensor, First
    immunosensor
  • 1976 First bedside artificial pancreas (Miles)
  • 1980 First fibre optic pH sensor for in vivo
    blood gases (Peterson)
  • 1982 First fibre optic-based biosensor
  • 1983 First surface plasmon resonance (SPR)
    immunosensor
  • 1984 First mediated amperometric biosensor
    ferrocene used with glucose oxidase for
    glucose detection

10
  • 1987 Blood-glucose biosensor launched by
    MediSenseExacTech
  • SPR based biosensor by Pharmacia BIACore
  • 1992 Hand held blood biosensor by
    i-STAT
  • 1996 Launching of Glucocard
  • 1998 Blood glucose biosensor launch by
    LifeScan FastTake
  • 1998 Launch of LifeScan FastTake blood
    glucose biosensor
  • 1998 Merger of Roche and Boehringer Mannheim to
    form Roche Diagnostics 1
  • LifeScan purchases Inverness Medical's
    glucose testing business for 1.3billion
  • 2001 To 2015 Microorganism and nano
    technology to biosensors
  • Quantomdots,
    nanoparicles, nanowire, nanotube, etc

11
Your welcome To this subject
12
What are biosensors?
  • Devices that analyze biological samples to better
    understand structure and function and for
    diagnostics
  • Uses for biosensors
  • Molecule analysis (DNA and proteins)
  • Food safety
  • Diagnostics
  • Medical monitoring
  • Detection of biological weapons
  • Rapid analysis and detection

13
Biosensors
  • Advantages
  • Rapid detection
  • Small volumes of samples needed
  • Can be used by the patient (blood glucose
    monitor)
  • Disadvantages
  • Cost
  • May require expertise to use
  • Sample collection can be painful

14
Types of biosensors
  • Electrochemical
  • Temperature sensitive
  • Photosensitive
  • Pressure sensitive
  • Motion sensitive
  • Chemical sensitive

15
Category biosensors for biochemical and
biological function and structure
  • Biocatalytic (eg, enzymes)
  • Immunological (eg, antibodies)
  • (DNA Nucleic acid (eg,

16
Common biosensors
  • Blood glucose monitors
  • Heart and blood pressure monitors
  • Pacemakers
  • HIV and pregnancy tests

17
Blood glucose monitors
  • Used by diabetics to measure blood glucose
    concentration
  • Helps patients determine their insulin dose
  • Uses electrochemistry for detection

18
biosensors
A biosensor consists of two components a
bioreceptor and a transducer. The bioreceptor
is a biomolecule that recognizes the target
analyte whereas the transducer converts the
recognition event into a measurable signal.
19
Schematic illustration of a Biosensor
signal prossing
monitor
amplification
transducer
bioreceptor

20
Introduction
  • Bioreceptor
  • Incorporation of a biomolecule in order to detect
    something

Recognition Layer
Species to be detected (analyte)
Transducer
Electronics
Signal
21
bio sample Analyte
  • Sugar
  • urea
  • cholesterol
  • ethanol

glutamic acid lactic acid Penicillin toxin
  • many amino acids
  • Peptide
  • vitamin
  • aspirin
  • phosphate

22
bioreceptor
  • Enzyme
  • Antibody
  • (DNA)
  • (receptor)
  • (microorganism)
  • ( tissue)
  • (cell)
  • (organel)

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Saraju P.Mohanty and Elias Kougianos,2006
25
Bioreceptors
  • Enzyme

Enzyme is a large protein molecule that acts as a
catalyst in chemical reactions. Enzymes are often
chosen as bioreceptors based on their specific
binding capabilities as well as their catalytic
activity
26
Enzyme
Enzymes are folded polypeptides (polymers
of amino acids) which catalyze chemical
reactions without being used up in the
conversion of substrates to products.
Enzymes are proteins with high catalytic
activity and selectivity towards substrates.
27
Enzyme
28
Advantage and disadvantage of Enzyme
Advantage connected to the object High
selection catalytic activity increase
sensitivity Fastly performance highest consumption
Disadvantage Expensive When immobilization
enzyme on transducer, loses part of its
activitiesBecause inactivity , shortly lose its
activities
29
Bioreceptors
  • Antibody

Antibodies are biological molecules that exhibit
very specific binding capabilities for specific
structure (antigens).
  • Antigen

membrane
It can be recognized by antibody.
30
biosensors-based antibody also called
Immunosensors
Antibodies usually immobilize on level of
transducer by the amino, carboxyl, aldehyde,
sulfide groups. Bonding antibodies to the
antigen is stronger and more specific than
bonding substrate of the enzyme,.
31
  • Advantage
  • High selectiveVery sensitiveTheir bond is
    very strong.

Disadvantage Loss of catalytic effect
32
Bioreceptors
  • DNA structure

Another biorecognition mechanism involves
hybridization of deoxyribonucleic acid (DNA) or
ribonucleic acid (RNA), which are the building
blocks of genetics.
  • Four chemical bases
  • adenine(A), guanine (G),
  • cytosine (C), thymine (T)

33
  • Nucleic acid hybridization

Principles of DNA biosensors
(Target Sequence)
Probe DNA is useful for recognation genetic
disease , cancer, viral infection
34
Mark
  • Antibody
  • Probe DNA

35
The complementarity of adenine-thymine and
cytosine-guanosine pairing in DNA forms the
basis for the specificity of biorecognition in
DNA biosensors (Fig. 2).
36
receptors
37
Introduction to Biosensors
Bioreceptor
Transducer
Absorption
Fluorescence
Antibody
Optical
Interference
potentiometric
Enzyme
Electrochemical
amperometric
conductimetric
Nucleic Acid (DNA)
Mass based
Cell
Temperature based
Dielectric properties
Electric Magnetic
Permeability properties
MIP
Voltage or Current
38
  • Discriminative Membrance and membrance proce
    are essential component of a biosensors
  • Selective prevalence Prevent foulingEliminate
    interferenceControl Emission of
    analyte Preserving the environment enzymes 
    Protection against mechanical stresses

39
transducer
40
transducer
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  • Electrochemical

The basic principle for this class of biosensors
is that chemical reactions between immobilized
biomolecule and target analyte produce or
consume ions or electrons, which affects
measurable electrical properties of the
solution, such an electric current or potential
(Thevenot et al. 1999).
  • electrochemical DNA biosensors

44
Amperometric Amperometric biosensors are the
most widespread class of biosensors .
Amperometric biosensors are very sensitive
and more suitable for mass production than
the potentiometric ones (Ghindilis et al.
1998).
Platinum, gold, silver, rustproof steel or
carbon based material electrodes
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Potentiometric
This transducer measures difference
in potential that is generated across an
ion-selective membrane separating two solutions
at virtually zero current flow. Nearly all
potentiometric sensors, including glass
electrodes, metal oxide based sensors as well as
ion-selective electrodes, are commercially
available. Moreover, they can be easily
mass-fabricated in the miniature formats
using advanced modern silicon or thick-film
technologies (Koncki 2007).
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Conductometric
  • A technique that works on ion changes and
    changes in ion concentration is
    measured.Solutions are containing electron
    conductor ions.The magnitude of the conductivity
    changed by chemical reaction.  In this method,
    platinum or gold electrodes are used to measure
    changes in ion.

49
  • Piezoelectric (mass-sensitive)

These biosensors are based on the coupling of the
bioelement with a piezoelectric component,
usually a quartz-crystal coated with gold
electrodes.
Many types of materials (quartz, tourmaline,
lithium niobate or tantalate, oriented zinc oxide
or aluminium nitride) exhibit the piezoelectric
effect.
50
Calorimetric (thermometric)
These biosensors are constructed by
immobilization of biomolecules onto
temperature sensors. Once the analyte comes
in contact with the biocomponent, the
reaction heat which is proportional to the
analyte concentration is measured. The
measurement of the temperature is via a
thermistor, and such devices are called as
enzyme thermistors. Calorimetric biosensors
were used for food, cosmetics, pharmaceutical
and other component analysis (An- tonelli et al.
2008, Bhand et al. 2010, Ramanathan et al. 2001,
Vermeir et al. 2007).
51
Opticometric
  • Absorption spectroscopy
  • fluorescence spectroscopy
  • internal reflection spectroscopy
  • Light scattering

52
Immobilizatiom
53
Immobilizatiom
  • The most commonly used immobilization
    techniques for construction of biosensors
    are physical adsorption (Nanduri et al.
    1997), covalent binding (Schuhmann et al.
    1990), matrix entrapment (Gupta and Chaudhury
    2007), inter molecular cross-linking (Nenkova
    et al. 2010) and membrane entrapment (Pancrazio
    et al. 1998, Scouten et al. 1995, Sharma et al.
    2003).

54
1. Adsorption
  • The physical adsorption utilizes a
    combination of Van der Waals and hydrophobic
    forces, hydrogen bonds, and ionic forces to
    attach the biomaterial to the surface of the
    sensor.
  • Many substrates such as cellulose,
    collodion, silica gel, glass, hydroxyapatite
    and collagen are well known to adsorb
    biocomponents.
  • This method is very simple, however, employed
    forces are not very strong and biomolecules
    attached by this method may be released or not
    persist.

55
2. Covalent binding
  • The sensor surface is modified to acquire a
    reactive group to which the biological materials
    can be attached.
  • formation of a stable covalent bond between
    functional groups of the bioreceptor components
    and the transducer.
  • In case of enzymatic biosensors it is through the
    functional group in the enzyme which is not
    essential for its catalytic activity.
  • Usually, nucleophilic functional groups
    present in amino acid side chains of
    proteins such as amino, carboxylic,
    imidazole, thiol, hydroxyl etc.
    (SH,OH,COOH,NH) are used for coupling.

56
Covalent binding
  • This method improves uniformity, density
    and distribution of the bioelements,
  • as well as reproducibility and
    homogeneity of the surfaces.
  • Covalent immobilization may decrease or
    eliminate some common problems such as
    instability, diffusion and aggregation, or
    inactivation of biomolecules. This occurs when
    biomolecules are immobilized on sensor surfaces
    by polymer matrices.
  • In this method, the enzyme can not be
    washed out
  • For this purposes the reagents such as
    glutaraldehyde, carbodiimide, succinimide
    esters, maleinimides and periodate are often
    used for covalent immobilization (Collings and
    Caruso Frank 1997).
  • PH and temperature should be low

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3. Matrix entrapment
  • In this case biomolecules are trapped
    within the polymeric gel matrix.
  • For this method the polyacrylamide, starch,
    alginate, pectate, polyvinyl alcohol,
    polyvinyl chloride, polycarbonate,
    polyacrylamide, cellulose acetate and silica gel
    are often be used.
  • Matrix entrapment has disadvantage of possible
    leakage of the biological species during use,
    resulting in a loss of activity (Collings and
    Caruso Frank 1997).

59
  • The immobilization is done either by physical
    entrapment or chemical attachment.

Physical Entrapment
Bioreceptor (Antibody, Enzyme, Cell, )
polymer solution ? polymerization
60
4. Cross-linking
  • For intermolecular cross-linking of
    biomolecules biofunctional or multifunctional
    reagents such as glutaraldehyde, hexamethylene
    di-isocyanate, 1,5-difluoro
    2,4-dinitrobenzene and bisdiazobenzidine-2,2-d
    isulphonic acid, etc., are used.
  • The most common cross-linking agent in
    biosensor applications is glutaraldehyde,
    which couples with the lysine amino groups
    of enzymes.
  • bridging between functional groups on the outer
    membrane of the receptor by multifunctional
    reagents to transducer. The cells can be bounded
    directly onto the electrode surface or on a
    removable support membrane, which can be placed
    on the transducer surface

61
disadvantages the enzyme layer
formed is not rigid there are higher
demands for amount of biological material
cross-linking can cause the formation of
multilayers of enzyme, which negatively
affects the activity of the immobilized layers.
Moreover larger diffusional barriers may
delay interactions (Collings and Caruso
Frank 1997).
62
  • 5. Encapsulation
  • In this method a porous encapsulation
    matrix (e.g. lipid bilayers) is formed around the
    biological material and helps in binding
    it to the sensor.
  • -Cellulose acetate- Polycarbonate-
    Collagen- Teflon
  • Other approach for encapsulation uses solgel
    method for the immobilization of biological
    molecules in ceramics, glasses, and other
    inorganic materials using.
  • These matrices allow optical monitoring of the
    chemical interactions since they are optically
    transparent. The solgel process can be
    performed at room temperature and which
    protects biomolecules against
    denaturation.

63
microencapsulation
Biomolecules immobilized by this procedure are
very stable but achieving of sol-gels with
reproducible pore sizes seems to be still
an obstacle. Problems such as diffusional
limitations inside the porous network,
brittleness of the glassy matrix,
reproducibility or discrepancies in the
preparation procedures has to be solved before
this procedure can be used for routine
application (Collings and Caruso Frank 1997).
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Two factors play a role in the design of a
suitable Biosensors
  • Appropriate method immobilized bioreceptors in
    solid surface that will extend the life ,
    sensitivity and stability
  • Select the appropriate trancducer

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  • Amplifier

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The main tasks in the development of a
Biosensor selection an appropriate
bioreceptor molecules(biochemistry and biology)
Select an appropriate immobilization (chemistry)
Select a suitable transducer (electrochemistry
and physics) Biosensors are designed according
to the measurement range (kinetics and mass
transfer )To minimize interference and packaging
Biosensors
Thus, interdisciplinary cooperation is essential
for the successful development of Biosensors
70
The accuracy and reproducibility
Insensitive to temperature
Insensitive to environmental interference
The response rate
Requirements needed for successful
commercialization of biosensors
Costs and capital Biosensor
Prevention of pollution
Physical strength
71
Application in agriculture and food products
72
  • Biosensor Using a banana (bananatrod)Biosensors
    detector soil pathogensBiosensors tracking E.
    coliBiosensors mercuryBiosensors to detect
    neurological defectsGold Biosensor to detect
    cancer cellsWarning sensors thirstBiosensor for
    measuring aflatoxin Biosensors ureaBiosensors
    penicillinBlood Glucose Biosensors

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NANOBIOSENSORS
Section2
75
Abstract
  • The revolution of nanotechnology in molecular
    biology gives an
  • opportunity to detect and manipulate atoms and
    molecules at the
  • molecular and cellular level.

76
What is a Nanobiosensor?
  • A biosensor is a measurement system for the
    detection of an analyte that combines a
    biological component with a physicochemical
    detector, and a nanobiosensor is a biosensor that
    on the nano-scale size.
  • Nanobiosensor
  • Transducer Detector Biological Recognition
    Element (Bioreceptor)

  • Living biological system
  • (cell, tissue or whole organism)

  • Biological molecular species
  • (antibody, enzyme, protein)

77
  • Principle of Detection
  • Piezoelectric Mass
  • Electrochemical Electric distribution
  • Optical Light intensity
  • Calorimetric Heat
  • Types of Nanobiosensors
  • Optical Biosensors Nanotube Based Biosensors
  • Electrical Biosensors Viral Nanosensors
  • Electrochemical Biosensors Nanoshell
    Biosensors
  • Nanowire Biosensors

78
  • Optical Nanobiosensors
  • A sensor that uses light to detect the effect of
    a chemical on a biological system. Kopelman et
    al.
  • The small size of the optical fibers allow
    sensing intracelular physiological and biological
    parameter in micro-environment.
  • Two kind of fabrication methods for optical
    fiber tips
  • 1) Heat and Pull
    Method
  • 2) Chemical
    Etching

79
  • Nanowire Field Effect Nanobiosensors(FET)
  • Sensing Element
  • Semiconductor channel (nanowire) of
    the transistor.
  • The semiconductor channel is fabricated using
    nanomaterials such
  • a carbon nanotubes,metal oxide nanowires or Si
    nanowires.
  • Very high surface to volume radio and very large
    portion of the atoms are located on the surface.
    Extremely sensitive to environment

80
Applications of Nanobiosensors
  • Biological Applications
  • DNA Sensors Genetic monitoring, disease
  • Immunosensors HIV, Hepatitis,other viral diseas,
    drug testing, environmental monitoring
  • Cell-based Sensors functional sensors, drug
    testing
  • Point-of-care sensors blood, urine,
    electrolytes, gases, steroids,
  • drugs, hormones, proteins, other
  • Bacteria Sensors (E-coli, streptococcus, other)
    food industry,
  • medicine, environmental, other.
  • Enzyme sensors diabetics, drug testing, other.
  • Environmental Applications
  • Detection of environmental pollution and toxicity
  • Agricultural monitoring
  • Ground water screening
  • Ocean monitoring

81
Future Application
  • Cancer Monitoring
  • Nanobiosensors play a very important role for
    early cancer detection in
  • body fluids.
  • The sensor is coated with a cancer-specific
    antibody or other
  • biorecognation ligands. The capture of a cancer
    cell or a target protein
  • yields electrical, optical or mechanical signal
    for detection. Professor
  • Calum McNeil detection of cancer proteins that
    cause MRSA
  • Identification of Biomarkers
  • ?
  • Validation of Cancer Biomarkers
  • ?
  • Cancer Biomarkers
  • ?
  • Ligands / Probes Developments
  • ?
  • Cancer Diagnostics Biosensor ? Detector

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Section 3

84
  • Extensive activity spread throughout Engineering
    and Science.
  • Goals
  • Biosensor devices (really biointerface devices
    since both sensing and actuating are of
    interest).
  • Inference and control algorithms for use with
    such devices.
  • Basic science to clinical medicine.

85
Recent Work
  • Development of rapid lateral flow assays for
  • CD4 cells from human blood
  • Cryptosporidium parvum
  • Pathogenic bacteria (i.e.-Bacillus anthracis,
    Escherichia coli)
  • Dengue virus (serotype specific)
  • Herbicides (Alachlor, imazethapyr)
  • Development of microtiter plate assays for cell
    culture supernatants
  • Cholera toxin
  • Insulin
  • Visualization and quantification of cholera toxin
    binding to epithelial cells
  • Encapsulation of DNA oligonucleotides for
    detection of
  • protective antigen from B. anthracis allowed
    for multi-analyte
  • analysis proof of principle

86
Assay Overview
  • Biorecognition elements can be conjugated to
    liposomal bilayer
  • Antibodies
  • Streptavidin or Protein A/G, Enzymes, Other
    Proteins
  • Small-molecule analytes
  • Fluorophores
  • Hydrophilic molecules can be encapsulated within
    interior cavity
  • Enzymes
  • Fluorophores
  • Electrochemical markers
  • Oligonucleotides
  • Assay types
  • Sandwich immunoassays
  • Sandwich hybridizations
  • Competitive assays
  • Assay formats
  • Lateral-flow assays
  • Microfluidic devices
  • Sequential-injection analysis
  • Microtiter plates

87
mRNA detection
  • mRNA extracted from culture and amplified using
    NASBA
  • Sandwich-hybridization of amplified RNA target
    between reporter probe-tagged liposomes and
    immobilized capture probes
  • Synthetic DNA analogue used for development work
  • Assay proven successful for the detection of mRNA
    from E. coli, B. anthracis, Dengue virus and C.
    parvum
  • DNA-tagged liposomes in a sandwich hybridization
    assay for B. anthracis atxA mRNA. Limit of
    detection (bkgd3xStDev) 0.11 nM, Assay range
    0.5-50 nM, CV 4.4, Assay time 1.75 hours

Analytical Bioanalytical Chemistry, vol. 386 (6),
p. 1613 1623 (2006)
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  • Section4

90
Electrochemical DNA Sensors
  • Harnesses specificity of DNA
  • Simple assembly
  • Customizable
  • Vast uses for small cost

91
DNA Specificity
  • Hydrogen bonding between base pairs
  • Stacking interaction between bases along axis of
  • double-helix

92
Principles of DNA biosensors
  • Nucleic acid hybridization

(Target Sequence)
(Hybridization)
(Stable dsDNA)
ssDNA (Probe)
Source http//cswww.essex.ac.uk
93
Whole Cell Sensors
Source http//www.whatsnextnetwork.com/technology
/media/cell_adhesion.jpg
94
Whole Cell Sensors
  • Harness normal genetic processes
  • May detect dozens of pathogens
  • Modifiable/customizable
  • Reports bioavailability
  • Temperature/pH sensitive
  • Short shelf-life

95
Whole Cell Sensors
Source Daunert et al., 2000
96
Summary
  • Use of biomolecules in sensors offers
  • Extreme sensitivity
  • Flexibility of use
  • Wide array of detection
  • Universal application
  • But still maintains challenges of
  • pH/Temperature sensitivity
  • Degradation
  • Repeatable use
  • Regardless of challenges
  • Biosensors will permeate future society

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ELECTROCHEMICAL BIOSENSORS
  • - Produces an electrical signal that is related
    to the concentration of an analyte
  • - Biological recognition processes are converted
    into quantitative amperometric or potentiometric
    response
  • - Two categories depending on the nature of the
    biological recognition process
  • A. Biocatalytic Devices
  • - Utilizes enzymes, cells, tissues as immobilized
    biocomponents
  • B. Affinity Sensors
  • - Utilizes antibodies, membrane receptors,
    nucleic acids

99
ELECTROCHEMICAL BIOSENSORS
  • A. Enzyme-Based Electrodes
  • - Enzymes are proteins that catalyze chemical
    reactions in living things
  • - Based on coupling a layer of an enzyme with an
    electrode
  • (enzyme is immobilized on an electrode)
  • - Electrode serves as a transducer
  • - Very efficient and extremely selective

100
A. Enzyme-Based Electrodes Enzymes
(biocatalytic) layer immobilized on an electrode
Electrode
Biocatalytic Layer
101
ELECTROCHEMICAL BIOSENSORS
A. Enzyme-Based Electrodes - Polymeric films are
used to entrap enzyme (Nafion, polypyrrole) Enzym
e may be trapped - between electrode and a
dialysis membrane - by mixing with carbon paste -
by surface adsorption - by covalent
binding Applications - Useful for monitoring
clinical, environmental, food samples
102
ELECTROCHEMICAL BIOSENSORS
AI. Glucose Sensors - For determination of
glucose in blood - For diagnosis and therapy of
diabetes Glucose O2 ? Gluconic acid
H2O2
Glucose
oxidase
103
ELECTROCHEMICAL BIOSENSORS
AII. Ethanol Sensors (Ethanol Electrodes) AIII.
Urea Electrodes AIV. Other Enzyme
Electrodes AV. Tissue and Bacteria Electrodes
104
ELECTROCHEMICAL BIOSENSORS
B. Affinity Biosensors - Based on selective
binding of certain biomolecules towards specific
species that triggers electrical signals -
Measures electrochemical signals resulting from
the binding process - Highly sensitive and
selective
105
ELECTROCHEMICAL BIOSENSORS
BI. Immunosensors - Based on immunological
reactions - Useful for identifying and
quantifying proteins
106
ELECTROCHEMICAL BIOSENSORS
BII. DNA Hybridization Biosensors - Nucleic acid
recognition layers are combined with
electrochemical transducers - Used to obtain
DNA sequence information - Electrochemical
response of DNA is strongly dependent on DNA
structure
107
ELECTROCHEMICAL BIOSENSORS
BII. DNA Hybridization Biosensors Other
Applications - For chemical diagnosis of
infectious diseases - For environmental
monitoring - For detecting drugs, carcinogens,
food containing organisms - For criminal
investigations
108
ELECTROCHEMICAL BIOSENSORS
BIII. Receptor-Based Sensors BIV. Molecularly
Imprinted Polymer Sensors
109
GAS SENSORS
  • -
  • For monitoring gases such as CO2, O2, NH3, H2S
  • - Device is known as compound electrode
  • - Highly sensitive and selective for measuring
    dissolved gases
  • - For environmental monitoring
  • For clinical and industrial applications
  • - Gas permeable membrane (teflon, polyethylene)
    is immobilized
  • on a pH electrode or ion-selective electrode
  • - Thin film of electrolyte solution is placed
    between
  • electrode and membrane (fixed amount, 0.1 M)
  • - Inbuilt reference electrode
  • - The target analyte diffuses through the
    membrane and comes
  • to equilibrium with the internal electrolyte
    solution

110
GAS SENSORS
- The target gas then undergoes chemical reaction
and the resulting ion is detected by the
ion-selective electrode - Electrode response is
directly related to the concentration of gas in
the sample - Two types of polymeric materials
are used Microporous and Homogeneous - Membrane
thickness is 0.01 0.10 mm - Membrane is
impermeable to water and ions
111
GAS SENSORS
CO2 Sensors NH3 Sensors Other Gas Sensing
Devices NO2 and SO2 H2S HF
112
GAS SENSORS
Oxygen Sensors - Based on amperometric
measurements (gas sensors discussed earlier are
potentiometric) - Consists of a pair of
electrodes (Ag anode and Pt cathode) in an
electrolyte solution - Electrodes are separated
by a gas-permeable hydrophorbic membrane -
Membrane may be teflon, silicon rubber,
polyethylene
113
References
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