BIOSENSORS

BIOSENSORS

INTRODUCTION

• Biosensors are analytical devices.
• Comprises of four components.
• The components are biological recognition, an interfaced transducer, amplifier, processor and display unit.
• The biological recognition relies on enzymes, whole cells, antibodies, or nucleic acids
• The signal transduction exploits electrochemical, optical, piezoelectric, magnetic, or thermal  interfaces
• Biosensors detect the presence or concentration of a biological analyte, such as a biomolecule, a biological structure, or a microorganism.
• They qualitatively analysis various substances by converting the biological actions of the substance into measurable signals.
• The Father of biosensors is Professor Leland C Clark Jnr.

PRINCIPLE

•  It is based on the principle of signal transduction.
• The bioreceptor first interacts with a specific analyte.
• This interaction is then measured by the transducer.
• The transducer detects and outputs a signal.
• The intensity of this output is directly proportional to the concentration of the analyte.
• The electronic system then amplifies and processes the signal.
• After processing the signal it is read out and displayed for monitoring.
• The biological material that binds to the analytes to be detected is usually immobilised.
• Contact is made between the transducer and the material.
• Conversion of the analyte may take place which releases heat, gas, electrons ions.

COMPONENTS OF BIOSENSOR

1. Biological element–  This component is used to bind to the target molecule.
   • It must be highly specific towards the targeted analyte.
   • It is stable under the storage condition and immobilised.
   • The biological element could be any microorganism, tissue, cell, organelle, nucleic acid, enzyme, enzyme component, receptor or an antibody.
   • It detects the presence of the target molecule in the test solution.
2. Physiochemical Transducer–  It measures the physical change that occurs due to the reaction at the bioreceptor.
   • It transforms the energy released in the reaction into measurable electrical output.
3. Detector – It is a microprocessor.
   • The signals generating from the transducer passes to the detector which then amplifies and analyses the signals.
   • The analysed data is converted to concentration units.
   • Then it is transferred to display or data storage device.

 

FEATURES OF AN IDEAL BIOSENSOR

• Specificity for the analytes.
• Reactions used should be independent of factors such as pH, temperature, stirring, etc.
• Its response should be linear.
• Sufficient sensitivity and selectivity.
• Speed of response should be sufficient.
• The device should be tiny and compatible biologically.
• The device should be cheap, easy to use and compatible for repeated use.

TYPES OF BIOSENSOR

1. Calorimetric Biosensors
2. Potentiometric Biosensors
3. Acoustic wave Biosensors
4. Amperometric Biosensors
5. Optical Biosensors
6. Piezoelectric biosensors
7. Glucose biosensors
8. Electrochemical DNA biosensors
9. DNA biosensors

CALORIMETRIC BIOSENSORS

• The analyte concentration is measured by the exothermic reactions catalyzed by enzymes.
• An analyte solution is passed through a small packed column.
• This column contains an immobilized enzyme.
• The temperature changes are usually determined by means of thermistors at the entrance and exit.
• Example: sulfate-reducing bacterial cytochrome c3 reductases that reduce heavy metals.

 

 

POTENTIOMETRIC BIOSENSORS

• It is a type of chemical sensor.
• They use ion-selective electrode
• They convert biological reactions to electronic signals.
• The reactions use and generate hydrogen ion.
• The generated hydrogen ion is detected and measured by the biosensor.
• An example of the potentiometric biosensor is urea biosensor.

 

ACOUSTIC WAVE BIOSENSORS

• These type of sensor uses piezoelectric material.
• They are mostly quartz crystals to generate acoustic waves.
• The surface of the piezoelectric materials is coated with antibodies.
• They bind to their complementary antigen present in the sample solution.
• As a result, the mass of analyte is increased.
• This changes their vibrational frequency.
• This is used to determine the number of antigens present in the solution.

 

AMPEROMETRIC BIOSENSOR

• This functions through the production of current.
• For the production of current a potential is applied between two electrodes.
• The magnitude of the current is proportional to the concentration of the substrate.
• Usually, redox reactions are measured by this biosensor.

 

OPTICAL BIOSENSOR

• This determines the difference in light absorption between the reactants and products of a reaction.
• This also measures the light output through the luminescent process.
• Using firefly enzyme luciferase for the detection of bacteria in food and clinical samples.

PIEZOELECTRIC BIOSENSORS

• Gold is used to detect the specific angle at which the electron waves are emitted when the analyte is exposed to laser light.
• The analyte substance vibrates under the influence of an electric field.
• The change in frequency of vibration is directly proportional to the mass of observed material.

GLUCOSE BIOSENSORS

• Gluconic acid is formed from glucose which reacts with glucose oxidase(GOD).
• This results in the production of two electrons and two protons.
• Higher the glucose content, higher oxygen consumption.
• Glucose content is detected by a potential electrode.

ELECTROCHEMICAL DNA BIOSENSORS

• Steps in electrochemical DNA hybridization biosensors
  • Formation of the DNA recognition layer
  • The occurrence of an actual hybridisation event
  • The hybridisation event transforms into an electrical signal

 

APPLICATION OF BIOSENSORS

1. Detection of pathogens in food
2. Used in clinical applications for diagnosis of diseases like diabetes mellitus, human interleukin, cardiovascular diseases, etc.
3. Can be applied in pharmaceutical industries for monitoring chemical parameters.
4. Potentiometric biosensors can be applied for the determination of pesticides.
5. Used for the detection of epigenetic modifications.

REFERENCES

1. https://www.sciencedirect.com/science/article/abs/pii/S0925400508002931
2. https://www.sciencedirect.com/science/article/pii/S0956566301001257