Amperometric Biosensors Introduction n Enzyme Catalyzed redox reactions

Amperometric Biosensors

Introduction n Enzyme Catalyzed redox reactions n The function of the enzyme is to generate or consume an electroactive species in a stoichiometric relationship with its substrate or target analyte n 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 n Three generations n 1 st generation: the normal product of the reaction diffuses to the transducer and causes electrical response n 2 nd generation: involves specific mediators between reaction and transducer to generate improved response

Introduction n 3 rd generation: reaction itself causes the response

Amperometric Glucose Biosensor n Developed by Updike and Hicks n First reported use of enzyme electrode n Glucose in blood-diagnosis of diabetes n O 2 detection n H 2 O 2 detection n Enzyme mediation

Glucose Biosensor – O 2 n Central – Pt cathode, surrounding Ag/Ag. Cl anode, KCl electrolyte solution n Teflon membrane n Cathode (0. 6 V) O 2 + 4 H+ +4 e 2 H 2 O n Anode 4 Ag + 4 Cl 4 Ag. Cl + 4 en Glucose +O 2 glucoseoxidase Gluconic acid + H 2 O

Glucose Biosensor – O 2

Glucose Biosensor – H 2 O 2 n Reverse polarity of electrodes for the O 2 set up n Replace Teflon membrane with cellulose acetate membrane n Cathode: 2 Ag + 2 Cl 2 Ag. Cl + 2 en Pt Anode (0. 6 V): H 2 O 2 O 2+2 H+ + 2 en Counter electrode: 4 H++O 2 2 H 2 O – 4 e-

Glucose Biosensor – H 2 O 2

Glucose Biosensor – redox mediators n Replace O 2 with synthetic e- acceptor to shuttle e- from the flavin redox center of the enzyme to the electrode n Measurements become insensitive to O 2 fluctuations, and can be carried out at lower potentials n Enzyme mediators – dimethyl ferrocene, medola blue

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

Common Enzyme electrodes Measured Species Enzyme Detected species Lactate dehydrgenase NADH Lactate oxidase H 2 O 2 Phenol Tyrosinase Quinone Cholesterol oxidase O 2

Some Commercial applications n YSI : Glucose/Lactate n Prostate specific antigen (PSA) n NOVA Bioprofile analyzer (PO 2, Gluc, Gln, Glu, Lactate)

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

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