Biosensors - PowerPoint PPT Presentation

View by Category
About This Presentation
Title:

Biosensors

Description:

A chemical sensor is a device that transforms chemical information (composition, presence of a particular element or ion, concentration, chemical activity, partial pressure.) into an analytically useful signal. The chemical information, mentioned above, may originate from a chemical reaction of the analyte or from a physical property of the system investigated. They can have applications in different areas such as medicine, home safety, environmental pollution and many others. – PowerPoint PPT presentation

Number of Views:266

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Biosensors


1
  • CHEMICAL SENSOR
  • PREPARED AND PRESENTED
  • BY
  • PWADUBASHIYI C. PWAVODI msC(20143883)
  • FELIX chibuzo obi msc(20144610)
  • MTHABISI MOYO(20143906)
  • Erine saurel guepp(20135813)
  • LECTURERALI ISIN

2
INTRODUCTION
  • DEFINITION
  • BRIEF EXPLANATION OF CHEMICAL SENSOR
  • GENERAL WORKING PRINCIPLE
  • CLASSIFICATION OF CHEMICAL SENSOR
  • DISCUSSION OF THE TYPES OF CHEMICAL SENSOR
  • SUMMARY/CONCLUSION
  • QUESTIONS FROM THE PRESENTATION

CHEMICAL SENSORS
3
INTRODUCTION
  • Definition of the Chemical Sensor
  • A chemical sensor is a device that transforms
    chemical information (composition, presence of a
    particular element or ion, concentration,
    chemical activity, partial pressure.) into an
    analytically useful signal. The chemical
    information, mentioned above, may originate from
    a chemical reaction of the analyte or from a
    physical property of the system investigated.
    They can have applications in different areas
    such as medicine, home safety, environmental
    pollution and many others.

CHEMICAL SENSORS
4
WORKING PRINCIPLE OF THE CHEMICAL SENSOR
  • Chemical sensors usually contain two basic
    components connected in series a chemical
    (molecular) recognition system (receptor) and a
    physicochemical transducer. In the majority of
    chemical sensors, the receptor interacts with
    analyte molecules. As a result, its physical
    properties are changed in such a way that the
    appending transducer can gain an electrical
    signal.
  • Receptor The function of the receptor is
    fulfilled in many cases by a thin layer which is
    able to interact with the analyte molecules,
    catalyze a reaction selectively, or participate
    in a chemical equilibrium together with the
    analyte. The receptor layer can respond
    selectively to particular substances or to a
    group of substances.

CHEMICAL SENSORS
5
WORKING PRINCIPLE OF THE CHEMICAL SENSOR
  • The term molecular recognition is used to
    describe this behavior. Among the interaction
    processes, the most important for chemical
    sensors are adsorption, ion exchange and
    liquid-liquid extraction. Primarily these
    phenomena act at the interface between analyte
    and receptor surface.
  • Transducer Nowadays, signals are processed
    almost exclusively by means of electrical
    instrumentation. Accordingly, every sensor should
    include a transducing function, i.e. the actual
    concentration value, a non-electric quantity must
    be transformed into an electric quantity,
    voltage, current or resistance. Some of them
    develop their sensor function only in combination
    with an additional receptor layer. In other
    types, receptor operation is an inherent function
    of the transducer.

CHEMICAL SENSORS
6
DIAGRAM OF CHEMICAL SENSOR
CHEMICAL SENSORS
7
CLASSIFICATION OF CHEMICAL SENSOR
  • Chemical sensors may be classified according to
  • The operating principle of the transducer.
  • The type of substance either, chemicl,biochemical
    or physical( in terms of optical) it is sensing
    from its vicinity.
  • And they types include the folowing
  • Optical devices transform changes of optical
    phenomena, which are the result of an interaction
    of the analyte with the receptor part.
  • Electrochemical devices transform the effect of
    the electrochemical interaction analyte -
    electrode into a useful signal.
  • . Electrical devices based on measurements, where
    no electrochemical processes take place, but the
    signal arises from the change of electrical
    properties caused by the interaction of the
    analyte.

CHEMICAL SENSORS
8
CLASSES OF THE CHEMICAL SENSOR
  • 4. Mass sensitive devices transform the mass
    change at a specially modified surface into a
    change of a property of the support material.
  • 5. Magnetic devices based on the change of
    paramagnetic properties of a gas being analysed.
    These are represented by certain types of oxygen
    monitors.
  • 6. Thermometric devices based on the measurement
    of the heat effects of a specific chemical
    reaction or adsorption which involve the analyte.
    for example in the so called catalytic sensors
    the heat of a combustion reaction or an enzymatic
    reaction is measured by use of a thermistor.
  • 7. Other physical properties as for example X-,
    p- or r- radiation may form the basis for a
    chemical sensor in case they are used for
    determination of chemical composition.

CHEMICAL SENSORS
9
THERMOMETRIC SENSOR(CATALYTIC SENSOR)
  • A thermometric sensor can be set up easily by
    coating the surface of a thermometer with a
    catalytic layer. If the catalysed reaction has a
    considerable heat effect, then the reaction heat
    is preferably released locally at the active
    surface.Thermistors are micro thermometers useful
    as a basis for thermometric chemical sensors.
    They mainly consist of a semiconductor body with
    a temperature-dependent conductivity. As an
    example, a hydrogen sensor is created by coating
    a thermistor with a thin layer of black platinum
    Hydrogen traces in the air burn in the catalytic
    area. The reaction heat causes the temperature to
    rise

CHEMICAL SENSORS
10
  • The resulting temperature difference compared to
    ambient temperature can be measured in terms of
    resistance change. This difference depends on the
    hydrogen content in the air. Other combustible
    gases like hydrogen sulphide or carbon monoxide
    can be analysed by means of the same arrangement,
    but with different catalysts. It is essential to
    find a catalyst as selective as
    possible.Thermistors are available in numerous
    sizes and shapes. Common forms are balls with
    diameters as small as 0.1mm or thin films on a
    substrate.

CHEMICAL SENSORS
11
CATALYTIC SENSOR(PELLISTOR)
  • A catalyst is a chemical or substance that
    increases the rate of a reaction without being
    itself consumed.Heat is liberated as a result of
    a catalysed reaction.The temperature related to
    the chemical reaction is measured, using a
    calorimeter.Catalytic sensors are widely used to
    detect to detect low concentrations of flammable
    gases.
  • Pellistors are used to detect the presence of
    flammable gases.Any combustible gases present
    will oxidise on the catalyst bead, raising the
    temperature of the coil.The change in resistance
    is detected by comparing with an uncatalysed
    reference sensor.

CHEMICAL SENSORS
http//www.citytech.com/technology/pellistors.asp
12
Pellistor operating Modes.
  • The platinum coil is embedded in a ceramic pellet
    coated with a porous catalytic metal (palladium
    or platinum). This coil acts as both the heater
    and temperature sensor (like in the Mass Flow
    Controller). When the combustible gas reacts at
    the catalytic surface, the heat evolved increases
    the temperature inside the thermal shield.
  • This is raises the temperature of the platinum
    coil and thus its resistance
  • www.ipc.uni-tuebingen.de/weimar/pictures/chem_sens
    or.gif

CHEMICAL SENSORS
13
  • Pellistors have two operating modes
  • Isothermal, where an electronic circuit controls
    the current in the coil required to maintain
    constant temperature.
  • Non-isothermal, where the sensor is connected as
    part of a wheatstone bridge whose output voltage
    is a measure of the gas concentration.Catalytic
    sensors are widely used in the industries for
    detectation of flammable gases.

CHEMICAL SENSORS
14
OPTICAL CHEMICAL SENSORS.
  • Optical sensors represent a group of chemical
    sensors in which electromagnetic (EM) radiation
    is used to generate the analytical signal in a
    transduction element. The interaction of this
    radiation with the sample is evaluated from the
    change of a particular optical parameter and is
    related to the concentration of the analyte.
  • Typically, an optical chemical sensor consists of
    a chemical recognition phase (sensing element or
    receptor) coupled with a transduction element.
    The receptor identifies a parameter, e.g., the
    concentration of a given compound, pH, etc., and
    provides an optical signal proportional to the
    magnitude of this parameter. The function of the
    receptor is fulfilled in many cases by a thin
    layer that is able to interact with the analyte
    molecules, catalyse a reaction selectively, or
    participate in a chemical equilibrium together
    with the analyte. The transducer translates the
    optical signal produced by the receptor into a
    measurable signal that is suitable for processing
    by amplification, filtering, recording, display,
    etc.

CHEMICAL SENSORS
15
  • The figure below shows a schematic of the basic
    components of an optical chemical sensor, namely,
    the sample (analyte), the transduction platform,
    and signal processing element (electronics)
    leading to the optical signal measurement which
    is related to the analyte concentration.

Principal stages in the operation of a Chemical
pH Sensor.
Optical sensors can be based on various optical
principles (absorbance, reflectance,
luminescence, fluorescence), covering different
regions of the spectra (UV, Visible) and allowing
the measurement not only of the intensity of
light, but also of other related properties, such
as lifetime, refractive index, scattering,
diffraction and polarization.
CHEMICAL SENSORS
16
  • As an example, a luminescent sensor can be
    constructed by associating a sensing element,
    which emits light when in contact with a specific
    analyte, with a photodiode, which converts the
    energy of the incident light into a measurable
    signal.
  • OPTICAL DETECTION PRINCIPLES
  • For sensor applications only part of
    spectroscopic wavelength range is useful. From
    the practical point of view the following ways
    (Figure below) in which radiation can interact
    with an analytical sample are the most useful.
  • absorption
  • emission (fluorescence or phosphorescence)
  • reflexion and refraction

Fig. General arrangement of spectroscopic
measurements A light reflection, B
light refraction, C light absorption, D light
emission.
CHEMICAL SENSORS
17
  • Basically, Optical sensors employ optical
    transduction techniques and are based on reagents
    that change their optical properties on
    interaction with the analyte of interest. The
    most commonly measured optical properties are
    absorption, fluorescence intensity, and decay
    time, but in addition, reflectance, refractive
    index, light scattering, and light polarization
    have also been used as analytical parameters.A
    very good example of the Optical Chemical Sensor
    is the Optical Chemical PH Sensor.
  • OPTICAL CHEMICAL PH SENSOR
  • The Optical chemical pH sensors was developed in
    the last 2 years (August 2011-August 2013).
    Optical Chemical pH sensors could be
    reagent-based, namely, absorption- and
    fluorescence-based, as most optical pH sensors
    uses of colorimetric or fluorescent indicator
    dyes.

CHEMICAL SENSORS
18
  • In more specific terms, pH is of concern in life
    sciences, food and beverage processing, soil
    examination, and marine and pharmaceutical
    research to name a few. Thus the development of
    an optical pH sensor which can be applied in real
    world applications is not trivial.
  • WORKING PRINCIPLE OF THE OPTICAL CHEMICAL pH
    SENSOR.
  • Free hydrogen ions do not exist in aqueous
    solution and should be described as hydronium
    ions H3O. The hydrogen ion is very small and
    possesses very high charge density. These
    characteristics promote a reaction with a water
    molecule resulting in very strong association.
    Very often, the term hydrogen ion or proton is
    used, but it has to be kept in mind that this is
    only an accepted convention. Søren Sørensen,(a
    Danish chemist) defines pH as the negative
    logarithm of hydrogen ions concentration.
  • Today, the pH of a solution is defined in terms
    of a hydrogen ion H activity (sometimes called
    protons, or more correctly hydronium ions, H3O)

CHEMICAL SENSORS
19
  • pH -log aH  where aH is the activity of the
    hydrogen ions.The negative sign assures that pH
    of most solutions is always positive. Optical
    pH sensors exploit pH indicator dyes which are
    typically weak organic acids or bases with
    distinct optical properties associated with their
    protonated (acidic) and deprotonate (basic)
    forms. The absorption (color) or fluorescence
    properties of these dyes are modified with a
    change of concentration of the hydrogen ions
    (pH). A schematic representation of absorption-
    and luminescence-based sensing is shown in the
    Figure below.

CHEMICAL SENSORS
20
  • Schematic representation of the principle of (A)
    absorptionbased and (B) fluorescence-based pH
    sensing mechanisms.

Basically, the working Principle of the Optical
Chemical pH Sensors is passing Light through the
Analyte, then depending the the pH Concentration
of the Analyte, we will have different Degrees of
Absorption and Fluorescence of Light which are
given as Signals. These Signals are then
Processed and Amplified and digitally displayed
on a Screen. A Chemical Parameter (pH
Concentration) has been Converted to an
Electrical Signal.
CHEMICAL SENSORS
21
Coulometric Oxygen Sensors
  • A Coulometric oxygen sensor is system that
    employs two chambers with a specimen mounted as a
    sealed semi-barrier between them.
  • One chamber contains oxygen while the other is
    slowly purged with a stream of a carrier gas such
    as nitrogen.

CHEMICAL SENSORS
22
Mechanism of the Coulometric Oxygen sensor
  • As the oxygen gas permeates through the specimen
    into the carrier gas, it is transported to the
    coulometric detector where it creates an electric
    current with a magnitude that is proportional to
    the number of oxygen atoms flowing into the
    detector

CHEMICAL SENSORS
23
  • The solid state coulometric oxygen analyzer
    measures oxygen concentration by counting the
    number of electrons flowing through its circuit.
    Coulometric oxygen sensor is not consumed when it
    is exposed to oxygen, it does not require a
    constant purge to protect the sensor when the
    analyser is not being used and its lifetime is
    not dependant on how much oxygen it is exposed
    to. Coulometric oxygen sensors are suitable when
    oxygen concentrations are low in the gas to be
    measured.

CHEMICAL SENSORS
24
Summary of testing Method
  • The specimen is mounted as a sealed semi-barrier
    between two chambers at ambient atmospheric
    pressure. One chamber is slowly purged by a
    stream of nitrogen and the other chamber contains
    oxygen. As oxygen gas permeates through the film
    into the nitrogen carrier gas, it is transported
    to the coulometric detector where it produces an
    electrical current, the magnitude of which is
    proportional to the amount of oxygen flowing into
    the detector per unit time. Among that, oxygen
    gas is the testing gas and nitrogen gas is the
    carrier gas. Oxygen gas concentration of upper
    chamber is higher than that of lower chamber, due
    to which certain concentration difference is
    formed between two sides of specimen. During the
    permeability process, oxygen gas transmits from
    upper chamber through specimen into lower
    chamber.

CHEMICAL SENSORS
25
Instrument Calibration
  • The oxygen sensor used in this test method is a
    coulometric device that yields a linear output as
    predicted by Faraday's Law. In principle, four
    electrons are produced by the sensor for each
    molecule of oxygen that passes into it.
    Experience has shown under some circumstances the
    sensor may become depleted or damaged to the
    extent that efficiency and response are impaired.
    For that reason, this test method incorporates
    means for a periodic sensor evaluation. standard
    film is needed in instrument calibration. Since
    the data of standard film can directly influence
    the determination of calibration coefficient Q,
    special attention should be paid to film
    preparation and calibration repeatability.

CHEMICAL SENSORS
26
GAS SENSORS
  • Definition
  • Gas sensor is a subclass of chemical sensors.
  • -Gas sensor it a subclass chemical sensor that
    measures the concentration of gas in its
    vicinity. Gas sensor interacts with a gas to
    measure its concentration. Each gas has a unique
    breakdown voltage i.e. the electric field at
    which it is ionized. Sensor identifies gases by
    measuring these voltages. The concentration of
    the gas can be determined by measuring the
    current discharge in the device.

CHEMICAL SENSORS
27
Applications of Gas Sensor
  • Process control industries
  • Environmental monitoring
  • Boiler control
  • Fire detection
  • Alcohol breath tests
  • Detection of harmful gases in mines
  • Home safety
  • Grading of agro-products like coffee and spices

CHEMICAL SENSORS
28
Disadvantages
  • Low gas sensitivity due to the limited
    surface-to-volume ratio
  • Bulky or very heavy.
  • Consume lots of power in order to increase the
    sensitivity ( 500 degree)
  • Require risky high voltage to operate.

CHEMICAL SENSORS
29
Types of gas sensors
  • Carbone dioxide gas sensor
  • Carbone monoxide gas sensor
  • Hydrogen gas sensor

CHEMICAL SENSORS
30
1-Carbone dioxide (CO2) gas sensor
  • it is based on infrared light absorption (by CO2)
    principle.
  • The infrared detector detects the infrared light
    which is not absorbed by CO2 between source and
    detector. And then measures the heat produced by
    the non absorbed light. A voltage is produced due
    to the increasing of temperature in the infrared
    sensor.

CHEMICAL SENSORS
31
2- carbone monoxide gas sensor
  • It can either be battery-operated or AC powered.
  • Mostly the sensor will not sound an alarm at
    lower concentrations. (e.g. 100ppm).The alarm
    will sound within a few minutes at 400 ppm.So the
    function is specific to concentration-time.
  • Figure shows simple carbon monoxide sensor.

CHEMICAL SENSORS
32
Types of carbone monoxide gas sensors
  • Semiconductor sensor
  • Electrochemical sensor
  • Digital sensor
  • Biomimetic sensor (chem-optical or gel cell sensor

CHEMICAL SENSORS
33
3- hydrogen gas sensor
  • Palladium is commontly used to detect hydrogen
    because palladium selectively absorbs hydrogen
    gas and forms the chemical palladium hydride.
  • Types of hydrogen gas sensor
  • Optical fiber hydrogen sensors
  • Nanoparticle-based hydrogen microsensors
  • Diode based sensor

CHEMICAL SENSORS
34
GAS SENSING TECHNOLOGIES
  • Metal Oxide Based Gas Sensors
  • Capacitance Based Gas Sensors
  • Acoustic Wave Based Gas Sensors
  • Calorimetric Gas Sensors
  • Optical gas sensors
  • Electrochemical gas sensors

CHEMICAL SENSORS
35
NEW TECHNOLOGIES IN GAS SENSOR
  • Advanced technology today by using nanomaterials
    offers possibility to improve gas detection. we
    can have the new carbon nanotube with has one of
    the best surface-of-volume ratio which is very
    important for hight sensitivity fast response
    and low temperature.
  • The recent progress in developing MEMS
    (Micro-Electro-Mechanical Systems) leads to a
    new based H2 gas sensors. These sensors couple
    novel thin films as the active layer with a MEMS
    structure known as a Micro-Hotplate. This
    coupling results in a micro H2 gas sensor that
    has several unique advantages in terms of speed,
    sensitivity, stability and amenability to large
    scale manufacture.

CHEMICAL SENSORS
36
The new flexible carbon nano tube
CHEMICAL SENSORS
37
Some Companies involved in gas sensor fabrication
and prices
  • RAE system offers different types of sensors and
    prices depends on the performance of the sensor.
    ex QRAEII which can senses hydrogen sulfide
    oxygen and carbon( 176 pound),carbon monoxide and
    oxygen(132 pound) ,oxygen(88 pound per unit)..
  • Barharach
  • crowncon

CHEMICAL SENSORS
38
SUMMARY/CONCLUSION
  • DEFINITION
  • BRIEF EXPLANATION OF CHEMICAL SENSORS
  • GENERAL WORKING PRINCIPLES
  • CLASSIFICATION OF CHEMICAL SENSORS
  • SUMMARY/CONCLUSION
  • QUESTIONS FROM THE PRESENTATION

CHEMICAL SENSORS
39
QUESTIONS FROM THE PRESENTATION
  1. DEFINE CHEMICAL SENSORS
  2. OUTLINE ANY 5 OF THE TYPES OF CHEMICAL SENSORS WE
    HAVE
  3. EXPLAIN ANY ONE OF TYPES OF THE CHEMICAL SENSOR.

CHEMICAL SENSORS
40
  • THANK YOU FOR GOOD LISTENING

CHEMICAL SENSORS
About PowerShow.com