Glucose Biosensor

1. GLUCOSE
BIOSENSOR
- E K TA S I N G H

2. BLOOD GLUCOSE
• The blood sugar level, blood sugar concentration, or blood glucose level is the amount
of glucose present in the blood.
• The body tightly regulates blood glucose levels as a part of metabolic homeostasis.
• Different organs in the body require different concentration of glucose for their functioning.

3. REGULATION OF BLOOD GLUCOSE

4. BLOOD GLUCOSE LEVEL

5. GLUCOSE BIOSENSOR
• It is an analytical device used for the detection of glucose in the blood stream.
• There are different types of glucose biosensors based on their mechanism of action.

6. FIRST GENERATION GLUCOSE SENSOR
• Glucose enzyme electrode is used and molecular oxygen serves as the oxidising agent.
• The reaction is followed by measuring the decrease in the oxygen concentration using
Clark’s oxygen electrode. It was first designed in 1953 and used voltammetric principle.
• Glucose reacts with oxygen in the presence of glucose oxidase enzyme and gives
gluconic acid and hydrogen peroxide.
• The electrons generated in this process moves to the electrode.
• Higher the glucose, higher will be the oxygen consumed
• Cell current is directly proportional to the oxygen concentration.
• The glucose oxidase is immobilized in polyacrylamide gel on a gas-permeable
membrane covering the electrode, which consists of a platinum cathode and a silver
anode.

8. MAJOR DRAWBACKS OF FIRST
GENERATION GLUCOSE BIOSENSORS
• Amperometric measurement of hydrogen peroxide required a high operating potential
(0.6 V) for high selectivity.
• Restricted solubility of oxygen in biological fluids, which produced fluctuations in the
oxygen tension.
• Deactivation of the enzyme due to the production of hydrogen peroxide.

9. SECOND GENERATION GLUCOSE SENSOR
• The idea was developed to replace oxygen with other electron transfer agents which
were reversible, had appropriate oxidation potentials and whose concentrations could
be controlled.
• Transition metal cations and their complexes were mostly used. These agents are
usually called mediators.
• A variety of redox mediators, such as ferrocene, ferricyanide, quinines, methylene blue
etc were used to improve sensor performance.
• Usage of redox mediator eliminated the need of oxygen for electron transfer at the
electrode surface, thus overcoming the drawback of limited oxygen pressure observed
in the first generation biosensor.
• The lower redox potential of chosen mediators (0-2 V) results in no interference from
other electroactive species such as uric acid, ascorbic acid.

11. MAJOR DRAWBACKS OF SECOND
GENERATION GLUCOSE BIOSENSORS
• High competition between redox mediator and oxygen.
• Interference of other electroactive species lead to false and inaccurate results.
• Small size and highly diffusive nature of mediators poses problem of leaching of mediator
from intermediate region between enzyme and electrode surface.

12. • The third generation glucose biosensors are based on the direct electron transfer
between the active center of enzyme and the electrode.
• The intrinsic barrier to electron flow is the globular structure of glucose oxidase with
the active site, containing FAD/FADH2 redox cofactor, buried deep inside a cavity of ~
13 A◦ is a major hindrance for direct electron transfer.
• The possible approach discovered is the modification in the surface of the electrode.
• Molecules like Tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) are
incorporated on the surface of the electrode.
• These form a charge transfer complex and are highly reversible and stable to many
enzymes.
• These conducting salts can be built into electrodes in three ways: as single crystals, as
pressed pellets or as a paste with graphite powder.
THIRD GENERATION GLUCOSE SENSOR

15. NON-ENZYMATIC GLUCOSE BIOSENSORS
• The use of non-enzymatic electrodes as glucose sensors potentially promises a fourth
generation to analytical glucose oxidation
• • The active metal nanoparticle undergo a oxidation step that forms a hydrous oxide
layer OHads that mediate oxidation of the adsorbed species.

16. GLUCOSE BIOSENSORS BASED ON CARBON
NANOTUBE ELECTRODE ENSEMBLES
• The development of glucose biosensors based on carbon nanotube (CNT) Nano
electrode ensembles (NEEs) for the selective detection of glucose.
• CNTs have a high electrocatalytic effect and a fast electron-transfer rate.
• Glucose oxidase was covalently immobilized on CNT NEEs via carbodiimide chemistry
by forming amide linkages between their amine residues and carboxylic acid groups
on the CNT tips.
• The catalytic reduction of hydrogen peroxide liberated from the enzymatic reaction of
glucose oxidase upon the glucose and oxygen on CNT NEEs leads to the selective
detection of glucose.