Transcript 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
 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+ +4e2H2O
 Anode
4Ag + 4Cl4AgCl +
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 + 2Cl2AgCl + 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)
Gox(FADH2)
gluconic acid +
Gox(FADH2)+2Mox Gox(FAD)+2Mred+2H+
2Mred
2Mox + 2e-
Common Enzyme electrodes
Measured
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
 http://www.lsbu.ac.uk.html