Biosensors have four main components: a biorecognition element, transducer, signal processing device, and analyte or substrate. The biorecognition element specifically binds to the analyte, causing a change in a physical or chemical property that is detected by the transducer. Common types of transducers include calorimetric/thermal, optical, resonant, piezoelectric, and electrochemical. An example is a glucose biosensor, which uses the enzyme glucose oxidase as the biorecognition element. Glucose reacts with glucose oxidase, producing a product that can be detected electrochemically by a platinum electrode transducer.

1. Biosensors
Karthikumar Sankar
Kamaraj college of engineering and technology

2. Block Diagram of a Biosensor
Sample
(Analyte or
Substrate)
Biorecognition
Element
Transducer
Signal
Processing
Device
Olfactory
Membrane
Olfactory Nerve
Cell
Introduction to Biophotonics – Prasad - John Wiley & Sons © 2003

3. Definition
FATHER OF BIOSENSOR.
Professor Leland C Clark Jnr
(1918–2005)
Any device that has specific
biochemical reactions to
detect chemical compounds
in biological samples.

4. • 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

5. Biosensor components

8.  Calorimetric / Thermal Detection Biosensors.
 Uses Absorption / Production of Heat.
 Total heat produced/absorbed is ᾶ Molar Enthalpy/Total No. of
molecules in the rn.
 Temp. measured by Enzyme Thermistors.
Advantages:
• No need of Frequent recalibration.
• Insensitive to the Optical & Electrochemical Properties of the
sample.
Uses:
Detection of: (1) Pesticides .
(2) Pathogenic Bacteria.

16. GLUCOSE BIOSENSORS
• 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.

21. Calorimetric / Thermal Detection Biosensors.
 Uses Absorption / Production of Heat.
 Total heat produced/absorbed is ᾶ Molar Enthalpy/Total No. of molecules in the rn.
 Temp. measured by Enzyme Thermistors.
Advantages:
• No need of Frequent recalibration.
• Insensitive to the Optical & Electrochemical Properties of the sample.
Uses:
Detection of: (1) Pesticides .
(2) Pathogenic Bacteria.
Optical Biosensors.
 Colorimetric for colour - Measures change in Light Adsorption.
 Photometric for Light Intensity - Detects the Photon output.
Resonant Biosensors.
 An Acoustic Wave Transducer is coupled with Bioelement.
 Measures the change in Resonant Frequency.

22. Piezoelectric Biosensors.
 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.
 Change in Frequency ᾶ Mass of Absorbed material.
Ion Sensitive Biosensors.
 Are semiconductor FETs with ion-sensitive surface.
 Surface Electrical Potential changes when the ions & semiconductors interact.
 Measures the Change in Potential. Uses: pH Detection.
Electrochemical Biosensors.
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.
Uses: Detection of : Hybridized DNA, DNA- binding Drugs & Glucose Concentration.

23. Conductimetric Sensors.
 Measures Electrical Conductance/Resistance of the solution.
 Conductance Measurements have relatively Low Sensitivity.
 Electrical Field is generated using sinusoidal(ac) voltage, which helps in minimizing undesirable
effects like:
i. Faradaic processes.
ii. Double layer charging &
iii. Concentration polarization.
 Amperometric Biosensors.
 High Sensitivity Biosensor.
 Detects electroactive species present in the biological test samples.
 Measured Parameter – Current.
Potentiometric Sensors.
 Working Principle – When ramp voltage is applied to an electrode in solution, a current flow occurs
because of electrochemical reactions.
 Measured Parameter – Oxidation / reduction Potential of an Electrochemical rn.