Biomedical Engineering Reference
In-Depth Information
Plantinum
cathode
Reaction 4
Reaction 2
Cellulose acetate
membrane
Reaction 1
O-ring
H
2
C
2
Silver anode
Glucose
Reaction 3
Immobilized
enzyme
Polycarbonate
membrane
Reaction 1
Gluconic
acid
Glucose O
2
Oxidase
enzyme
H
2
O
2
Reaction 2
H
2
O
2
Platinum
Anode
O
2
2H
2e
Reaction 3
AgCI e
Silver
Reference
Ag
0
CI
Reaction 4
4H
O
2
Auxiliary
electrode
2H
2
O 4e
FIGURE 3.1
Schematic of a “fi rst-generation” glucose biosensor (based on a probe manufactured by
YSI Inc.).
macromolecules, hence imparting higher stability. Electropolymerized fi lms, particularly
poly (phenelendiamine) and overoxidized polypyrrole, have been shown particularly
useful for imparting high selectivity (based on size exclusion) while confi ning the GOx
onto the surface [17, 18]. Other widely used coatings include size-exclusion cellulose
acetate fi lms, the negatively charged (sulfonated) Nafi on or Kodak AQ ionomers, and
hydrophobic alkanethiol or lipid layers. The use of overlaid multilayers, combining the
properties of different fi lms, offers additional advantages. For example, alternate deposi-
tion of Nafi on and cellulose acetate was used for eliminating the interference of the neu-
tral acetaminophen and negatively charged ascorbic and uric acids, respectively [19].
Efforts during the 1990s focused on the preferential electrocatalytic detection of the
liberated hydrogen peroxide [20, 21, 22, 23]. This has allowed tuning of the detection
potential to the optimal region (
0.20 V vs Ag/AgCl) where most unwanted
background reactions are negligible. The remarkably high selectivity thus obtained was
coupled to a fast and sensitive response. Metallized (Ru,Rh,)-carbon [20, 21] and metal-
hexacyanoferrate [22, 23] based transducers have been particularly useful for enhanc-
ing the selectivity towards the target glucose substrate. Additional improvements can
be achieved by combining this preferential catalytic activity with a discriminative layer,
e.g. by dispersing rhodium particles within a Nafi on fi lm [24].
0.0 to
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