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Amperometric Biosensors

Amperometric Biosensors. Introduction. Enzyme Catalyzed redox reactions The function of the enzyme is to generate or consume an electroactive species in a stoichiometric relationship with its substrate or target analyte

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Amperometric Biosensors

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  1. Amperometric Biosensors

  2. Introduction • Enzyme Catalyzed redox reactions • The function of the enzyme is to generate or consume an electroactive species in a stoichiometric relationship with its substrate or target analyte • Amperometric transducer allows for the electrometrical reactions to proceed at the electrode surface, thus giving rise to a current

  3. Introduction - Amperometric Biosensor Schematic

  4. Introduction S+C enzyme P + C’ S = Substrate C = Cofactor / Coreactant P = Product C’ = Cofactor Product

  5. Introduction • Three generations • 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

  6. Introduction • 3rd generation: reaction itself causes the response

  7. Amperometric Glucose Biosensor • Developed by Updike and Hicks • First reported use of enzyme electrode • Glucose in blood-diagnosis of diabetes • O2 detection • H2O2 detection • Enzyme mediation

  8. Glucose Biosensor – O2 • Central – Pt cathode, surrounding Ag/AgCl anode, KCl electrolyte solution • Teflon membrane • Cathode (0.6V) O2 + 4H+ +4e- 2H2O • Anode 4Ag + 4Cl- 4AgCl + 4e- • Glucose +O2 glucoseoxidase Gluconic acid + H2O

  9. Glucose Biosensor – O2

  10. Glucose Biosensor – H2O2 • Reverse polarity of electrodes for the O2 set up • Replace Teflon membrane with cellulose acetate membrane • Cathode: 2Ag + 2Cl- 2AgCl + 2e- • Pt Anode (0.6V): H2O2 O2+2H+ + 2e- • Counter electrode: 4H++O2 2H2O – 4e-

  11. Glucose Biosensor – H2O2

  12. Glucose Biosensor – redox mediators • Replace O2 with synthetic e- acceptor to shuttle e- from the flavin redox center of the enzyme to the electrode • Measurements become insensitive to O2 fluctuations, and can be carried out at lower potentials • Enzyme mediators – dimethyl ferrocene, medola blue

  13. Glucose Biosensor – Redox mediators Glucose + Gox(FAD) gluconic acid + Gox(FADH2) Gox(FADH2)+2Mox Gox(FAD)+2Mred+2H+ 2Mred 2Mox + 2e-

  14. Common Enzyme electrodes

  15. Some Commercial applications • YSI : Glucose/Lactate • Prostate specific antigen (PSA) • NOVA Bioprofile analyzer (PO2, Gluc, Gln, Glu, Lactate)

  16. Other Applications • Glucose: meat freshness, fermentation • Rapid cell number monitor • Monitor of herbicides in surface waters • Amperometric and novel fluorescent DNA probes • Rapid electrochemical sensor for Iron

  17. References • A.G. Elie,Principles of Potentiometric and Amperometric Biosensors,University of Virginia,(2002) • P.V. Climent, M.L.M.Serralheiro, and M.J.F. Rebelo, Pure and Applied Chemistry 73, pp.1993-1999, 2001 • http://www.lsbu.ac.uk.html

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