2. BIOSENSOR
A BIOSENSOR IS AN ANALYTICAL DEVICE CONTAINING AN IMMOBILIZED
BIOLOGICAL MATERIAL (ENZYME, ANTIBODY, NUCLEIC ACID, HORMONE,
ORGANELLE OR WHOLE CELL) WHICH CAN SPECIFICALLY INTERACT WITH AN
ANALYTE AND PRODUCE PHYSICAL, CHEMICAL OR ELECTRICAL SIGNALS THAT
CAN BE MEASURED. AN ANALYTE IS A COMPOUND (E.G. GLUCOSE, UREA, DRUG,
PESTICIDE) WHOSE CONCENTRATION HAS TO BE MEASURED.
3. BLOOD GLUCOSE MONITORING IS A WAY OF
CHECKING THE CONCENTRATION OF
GLUCOSE IN THE BLOOD USING A
GLUCOMETER.
4. PURPOSE
• PROVIDES QUICK RESPONSE TO TELL IF THE SUGAR IS
HIGH OR LOW INDICATING A CHANGE IN DIET, EXERCISE
OR INSULIN.
• OVER TIME, IT REVEALS INDIVIDUAL OF BLOOD
GLUCOSE CHANGES.
5. NEED TO MONITOR BLOOD GLUCOSE
• REDUCES RISK OF DEVELOPING COMPLICATIONS WITH
DIABETES.
• ALLOWS DIABETICS TO SEE IF THE INSULIN AND OTHER
MEDICATIONS THEY ARE TAKING ARE WORKING.
• GIVES DIABETICS AN IDEA AS TO HOW EXERCISE AND FOOD
AFFECT THEIR BLOOD SUGAR.
• MAY PREVENT HYPOGLYCEMIA OR HYPERGLYCEMIA
6. INTRODUCTION
• BLOOD GLUCOSE MONITORING HAS BEEN ESTABLISHED AS A
VALUABLE TOOL IN THE MANAGEMENT OF DIABETES.
• A SERIES OF SUITABLE GLUCOSE BIOSENSORS HAVE BEEN
DEVELOPED LIKE POINT-OF-CARE DEVICES, CONTINUOUS
GLUCOSE MONITORING SYSTEMS AND NONINVASIVE GLUCOSE
MONITORING SYSTEMS
7. • DIABETES MELLITUS IS THE MOST COMMON ENDOCRINE DISORDER OF
CARBOHYDRATE METABOLISM.
• DIABETES MELLITUS (DM), IS A GROUP OF METABOLIC DISORDERS IN WHICH
THERE ARE HIGH BLOOD SUGAR LEVELS OVER A PROLONGED PERIOD.
DIABETES MELLITUS IS A DISEASE THAT PREVENTS YOUR BODY FROM
PROPERLY USING THE ENERGY FROM THE FOOD YOU EAT.
• WORLDWIDE, IT IS A LEADING CAUSE OF MORBIDITY(CONDITION OF BEING
DISEASED) AND MORTALITY(DEATH ON LARGE SCALE) AND A MAJOR HEALTH
PROBLEM FOR MOST DEVELOPED SOCIETIES.
8. • GLUCOSE BIOSENSOR ARE OF THE ELECTROCHEMICAL TYPE
BECAUSE OF THEIR BETTER SENSITIVITY, REPRODUCIBILITY,
EASY MAINTENANCE AS WELL AS THEIR LOW COST.
• ENZYMATIC AMPEROMETRIC GLUCOSE BIOSENSORS ARE THE
MOST COMMON DEVICES COMMERCIALLY AVAILABLE.
• AMPEROMETRIC SENSORS MONITOR CURRENTS GENERATED
WHEN ELECTRONS ARE EXCHANGED EITHER DIRECTLY OR
INDIRECTLY BETWEEN A BIOLOGICAL SYSTEM AND AN
ELECTRODE.
9. GENERALLY GLUCOSE MEASUREMENTS ARE BASED ON THE INTERACTIONS
WITH ONE OF THE THREE ENZYMES
I. HEXOKINASE
II. GLUCOSE OXIDASE (GOX)
III. GLUCOSE-1-DEHYDROGENASE (GDH)
GLUCOSE BIOSENSORS FOR SELF MONITORING OF BLOOD GLUCOSE ARE
USUALLY BASED ON THE TWO ENZYME FAMILIES- GLUCOSE OXIDASE AND
GLUCOSE-1-DEHYDROGENASE.
10. • THE IMMOBILIZED GLUCOSE OXIDASE CATALYZES THE OXIDATION OF
GLUCOSE BY MOLECULAR OXYGEN PRODUCING GLUCONIC ACID AND
HYDROGEN PEROXIDE.
• IN ORDER TO WORK AS A CATALYST, GOX REQUIRES A REDOX COFACTOR –
FLAVIN ADENINE DINUCLEOTIDE (FAD), WORKS AS AN INITIAL ELECTRON
ACCEPTOR AND IS REDUCED TO FADH2.
GLUCOSE + GOX –FAD+ GLUCOLACTONE + GOX – FADH2
• THE COFACTOR IS REGENERATED BY REACTING WITH OXYGEN, LEADING TO
THE FORMATION OF HYDROGEN PEROXIDE
GOX – FADH2 + O2 GOX – FAD + H2O2
• HYDROGEN PEROXIDE IS OXIDIZED AT A PLATINUM ELECTRODE. THE NUMBER
OF ELECTRON TRANSFERS, AT ELECTRODE SURFACE IS DIRECTLY
PROPORTIONAL TO THE NUMBER OF GLUCOSE MOLECULES PRESENT IN THE
BLOOD.
11. THREE STRATEGIES USED FOR THE ELECTROCHEMICAL SENSING
OF GLUCOSE ARE
• BY MEASURING OXYGEN CONSUMPTION
• BY MEASURING THE AMOUNT OF HYDROGEN PEROXIDE
PRODUCED BY THE ENZYME REACTION
• BY USING A DIFFUSIBLE OR IMMOBILIZED MEDIATOR TO
TRANSFER THE ELECTRONS FROM GOX TO THE ELECTRODE.
12.
13. TYPES OF GLUCOSE BIOSENSORS
• FIRST GENERATION GLUCOSE BIOSENSOR
• SECOND GENERATION GLUCOSE BIOSENSOR
• THIRD GENERATION GLUCOSE BIOSENSOR
14. • 1ST GENERATION: THE NORMAL PRODUCT OF THE REACTION
DIFFUSES TO THE TRANSDUCER AND CAUSES ELECTRICAL
RESPONSE
• 2ND GENERATION: INVOLVES SPECIFIC MEDIATORS BETWEEN
REACTION AND TRANSDUCER TO GENERATE IMPROVED
RESPONSE
• 3RD GENERATION: REACTION ITSELF CAUSES THE RESPONSE
15. FIRST GENERATION GLUCOSE BIOSENSOR
• THE FIRST GENERATION GLUCOSE BIOSENSORS ESTIMATED GLUCOSE
CONCENTRATION IN THE SAMPLE BASED ON HYDROGEN PEROXIDE
PRODUCTION BY GLUCOSE OXIDASE UTILIZING DISSOLVED OXYGEN.
• BASED ON THIS TECHNOLOGY, YELLOW SPRING INSTRUMENT COMPANY,
LAUNCHED THE FIRST COMMERCIAL GLUCOSE BIOSENSOR IN MARKET IN 1975
FOR THE DIRECT MEASUREMENT OF GLUCOSE.
• THE USAGE OF THE MOST EXPENSIVE METAL PLATINUM FOR THE FABRICATION
OF THIS ELECTRODE RESTRICTED THE BIOSENSOR TO CLINICAL
LABORATORIES ONLY.
16. MAJOR DRAWBACKS OF FIRST GENERATION
GLUCOSE BIOSENSOR
• 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.
17. SECOND GENERATION GLUCOSE
BIOSENSORS
• THE SECOND GENERATION GLUCOSE BIOSENSOR UTILIZED REDOX MEDIATOR TO
TRANSFER ELECTRONS FROM THE ENZYME TO THE WORKING ELECTRODE SURFACE.
• 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.
• REDOX MEDIATOR ENHANCES THE ELECTRON TRANSFER BETWEEN THE REDOX
CENTER OF ENZYME AND THE ELECTRODE SURFACE.
18. MAJOR DRAWBACKS OF SECOND
GENERATION
• 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.
19. THIRD GENERATION GLUCOSE BIOSENSOR
• 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 IS A MAJOR HINDRANCE FOR
DIRECT ELECTRON TRANSFER.
• CARBON NANOTUBES IMMOBILIZED ÉLECTRODE SURFACE PROVIDE SUITABLE
ORIENTATION FOR ENZYME IMMOBILIZATION AND ESTABLISH CONNECTION
BETWEEN ELECTRODE SURFACE AND DEEPLY BURIED
