A device that uses specific biochemical reactions mediated by isolated enzymes, immunosystems, tissues, organelles or whole cells to detect chemical compounds usually by electrical, thermal or optical signals

• 
  A device that uses specific biochemical reactions mediated by isolated enzymes, immunosystems, tissues, organelles or whole cells to detect chemical compounds usually by electrical, thermal or optical signals.
  

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  The term biosensor is defined as a sensor incorporating biological elements such as enzymes, antibodies, receptors proteins, nucleic acids, cells, or tissue sections - as the recognition element, coupled to a transducer.
  

Block Diagram of a Biosensor

1. 
   Sample (Analyte or Substrate)
   
2. 
   BiorecognitionElement
   
3. 
   Transducer
   
4. 
   Signal Processing Device
   

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  The biological material is immobilized and a contact is made between the immobilized biological material and the transducer
  
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  The analyte binds to the biological material to form a bound analytewhich in turn produces the electronic response that can be measured.
  
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  Sometimes the analyte is converted to a product which could be associated with the release of heat, gas (oxygen), electrons or hydrogen ions. The transducer then converts the product linked changes into electrical signals which can be amplified and measured
  

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  Biosensors basically involve the quantitative analysis of various substances by converting their biological actions into measurable signals.
  

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  Generally the performance of the biosensors is mostly dependent on the specificity and sensitivity of the biological reaction, besides the stability of the enzyme.
  
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  Analyte diffuses from the solution to the surface of the Biosensor.
  
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  Analyte reacts specifically & efficiently with the Biological Component of the Biosensor.
  
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  This reaction changes the physicochemical properties of the Transducer surface.
  
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  This leads to a change in the optical/electronic properties of the Transducer Surface.
  
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  The change in the optical/electronic properties is measured/converted into electrical signal, which is detected.
  

The interaction of the analyte

(a) with the bioreceptor, which identifies the stimulus

(b) is designed to produce an effect measured by the transducer

(c), which converts it to an electrical signal. The output from the transducer is amplified

(d), processed

(e) anddisplayed
IDEAL BIOSENSORS

• 
  The output signal must be relevant to measurement environment.
  
• 
  The functional surface must be compatible with the transducer.
  
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  High specificity and selectivity (low interference).
  
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  Sufficient sensitivity and resolution .
  
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  Sufficient accuracy and repeatability
  
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  Sufficient speed of response
  
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  Sufficient dynamic range.
  
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  Insensitivity to environmental interference or their effects must be compensated
  

1. 
   Analyte
   
2. 
   Biological elements
   
3. 
   Transducer
   
4. 
   (processor)
   
5. 
   (monitor)
   

(What do you want to detect?)

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  It is the sensitive biological element or biological material (tissue ,microorganisms, organelles,cell receptors , enzymes, antibodies, nucleic acids,etc.) or bio- mimetic component that interacts (binds or recognises) the analyte under study.
  
• 
  The biologically sensitive elements can also be created by biological engineering.
  

1. 
   Enzymes
   
2. 
   Antibodies
   
3. 
   Hormone receptors
   
4. 
   Cells
   
5. 
   Cell organelle
   
6. 
   Tissues
   
7. 
   Membranes
   
8. 
   Micro organisms
   
9. 
   Nucleic acids
   
10. 
    Biomimetic materials
    

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  The principle of detection is the specific binding of the analyte of interest to the complementary biorecognition element immobilised on a suitable support medium.
  
• 
  The specific interaction results in a change in one or more physico-chemical properties (pH change, electron transfer, mass change, heat transfer, uptake or release of gases or specific ions) which are detected and may be measured by the transducer.
  

The transducer or the detector element transforms the signal resulting from the interaction of the analyte with the biological recognition element into another signal that can be more easily measured and quantified.

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  Biosensor is broadly classified into two classes:
  
• 
  I) On the basis of biological element
  
• 
  a) Enzyme Biosensor
  
• 
  b) Microbial Biosensor
  
• 
  c) Antibody Based.
  
• 
  II) ON THE BASIS OF TRANSDUCING ELEMENT
  

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  Calorimetric/Thermal Detection Biosensors.
  
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  Optical Biosensors.
  
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  Resonant Biosensors.
  
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  Piezoelectric Biosensors.
  
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  Ion Sensitive Biosensors.
  
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  Electrochemical Biosensors.
  

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  Conductimetric Sensors.
  
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  Amperometric Sensors.
  
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  Potentiometric Sensors.
  

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  Uses Absorption / Production of Heat.
  
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  Total heat produced/absorbed is ᾶ Molar Enthalpy/Total No. of moleculesin the rn.
  
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  Temp. measured by Enzyme Thermistors.
  

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  No need of Frequent recalibration.
  
• 
  Insensitive to the Optical & Electrochemical Properties of the sample.
  

Detection of: (1) Pesticides .

(2) Pathogenic Bacteria.
2)) Optical Biosensors.

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  Colorimetric for colour - Measures change in Light Adsorption.
  
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  Photometric for Light Intensity - Detects the Photon output.
  

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  An Acoustic Wave Transducer is coupled with Bioelement.
  
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  Measures the change in Resonant Frequency.
  

• 
  Uses Gold - To detect specific angle at which ȇ waves are emitted when the substance is exposed to laser light/crystals like quartz, which vibrates under the influence of an electric field.
  
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  Change in Frequency ᾶ Mass of Absorbed material.
  

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  Are semiconductor with ion-sensitive surface.
  
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  Surface Electrical Potential changes when the ions & semiconductors interact.
  
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  Measures the Change in Potential.
  

• 
  pH Detection.
  

Underlying Principle – Many chem.rns produce or consume ions or ȇs causing some change in the elctrical properties of the solution that can be sensed out & used as a measuring parameter.

Detection of :

• 
  Hybridized DNA
  
• 
  DNA- binding Drugs &
  
• 
  Glucose Concentration.
  

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  Measures Electrical Conductance/Resistance of the solution.
  

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  Conductance Measurements have relatively Low Sensitivity.
  

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  High Sensitivity Biosensor.
  
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  Detects electroactive species present in the biological test samples.
  
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  Measured Parameter – Current.
  

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  Working Principle – When ramp voltage is applied to an electrode in solution, a current flow occurs because of electrochemical reactions.
  
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  Measured Parameter – Oxidation / reduction Potential of an Electrochemicalrn.
  

1. 
   MEDICAL
   

Glucose monitoring in diabetes patients .

Medtronic glucose sensor - implants in major vein of heart.

b. Tumor cells are used as biosensors to monitor the susceptibility of

chemotherapeutic drugs.

c. Routine analytical measurement of folic acid, biotin, vitamin B12 and

d. Micro- and nanoscale biosensors—

Genome mutation detection , cancer detection & clinical diagnosis.

Bacterial-UTI , Human Immunodeficiency Virus (HIV) Detection, Hepatitis and Anthrax detection.

2. 
   BIO / PHARMACEUTICAL RESEARCH
   

1. 
   Quality assurance
   

c. Protein engineering .

4. 
   Drug discovery , evaluation monitor the manufacturing
   

ions by specific protein concentration or by using genetically

modified organisms.

6. 
   Aptamers are used for the detection of proteins –Thrombin , IgE ,
   

choline , which is the main cause in neurodegenerative diseases.

h. Microbiology: bacterial and viral analysis .

i. Biosensors are used in analysing micro dialysis samples.

j. Biosensors are used in biotechnological process such as to

determine proteins or peptides.

k. Biosensors are also used in determining intracellular proteins and

also plasmids.

l. Detection of cancer biomarkers – CEA , PSA , CA-125 &

Tumour necrosis factor .

3. 
   INDUSTRIAL / AGRICULTURAL
   

1. 
   Biosensors used in process control will be able to measure materials present in the process.
   

2. 
   Use of biosensors in industry will improve manufacturing techniques, this will allow for usage of wider variety of sensing molecules.
   

3. 
   Biosensors are used in controlling the industrial processes.
   
4. 
   Microbial sensor measure Ammonia & Methane.
   

4. 
   ENVIRONMENTAL
   

b. Biosensors are used in the BOD measurement during waste

water treatment.

c. Biosensors are used in the detection of poly aromatic

hydrocarbons present in water.

d. Environmental applications e.g. the detection of pesticides

and river water contaminants such as heavy metal ions.

e. Detection and determination of organophosphates .

5. 
   FOOD INDUSTRY
   

1. 
   Quality assurance in food industries , ex. E. Coli, Salmonella.
   

3. 
   Biosensors are used for detection of food freshness marker determining parameters in wine industry.
   

and growth promoters, particularly meat and honey.

e. Detection of toxic metabolites such as mycotoxins.

6. 
   BIODEFENCE
   

b. Remote sensing of airborne bacteria / virus ,

e.g. In counter bio-terrorist activities.

c. Detection system for biological welfare agent

d. Determining levels of toxic substances before and

after bioremediation.

e. Crime detection.

• 
  A common example of a commercial biosensor is the blood glucose biosensor, which uses the enzyme glucose oxidase to break blood glucose down.
  
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  In doing so it first oxidizes glucose and uses two electrons to reduce the FAD (a component of the enzyme) to FADH2.
  
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  This in turn is oxidized by the electrode (accepting two electrons from the electrode) in a number of steps.
  
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  The resulting current is a measure of the concentration of glucose. In this case, the electrode is the transducer and the enzyme is the biologically active component.