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
Amperometric transducer allows for the electrometrical reactions to proceed at the electrode surface, thus giving rise to a current
Introduction - Amperometric Biosensor Schematic
Introduction
S+C enzyme P + C’
S = Substrate
C = Cofactor / Coreactant
P = Product
C’ = Cofactor Product
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
Introduction
3rd generation: reaction itself causes the response
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
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
Glucose Biosensor – O2
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-
Glucose Biosensor – H2O2
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
Glucose Biosensor – Redox mediators
Glucose + Gox(FAD) gluconic acid + Gox(FADH2)
Gox(FADH2)+2Mox Gox(FAD)+2Mred+2H+
2Mred 2Mox + 2e-
Common Enzyme electrodesMeasured Species
Enzyme Detected species
Lactate Lactate dehydrgenase
NADH
Lactate Lactate oxidase
H2O2
Phenol Tyrosinase Quinone
Cholesterol Cholesterol oxidase
O2
Some Commercial applications
YSI : Glucose/Lactate Prostate specific antigen (PSA) NOVA Bioprofile analyzer (PO2, Gluc,
Gln, Glu, Lactate)
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
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
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