Chemical and biological sensors based on electroactive inorganic polycrystals - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 429

specifi c activity of the immobilized glucose oxidase. Since molar concentrations of the
enzyme and the polyelectrolyte in the casting solution are of a similar order of magni-
tude, the observed extremes indicate the formation of an enzyme-polyelectrolyte com-
plex at a molecular recognition level in concentrated organic solvents [164].
Enzyme containing Nafi on membranes prepared according to the proposed proto-
col have shown high specifi c activity and stability of immobilized glucose oxidase. As
expected, the simplicity of preparation provided high reproducibility. When the same
casting solution is used, the maximum deviation in membrane activity is 2%. This,

however, is also the precision limit for kinetic investigations.
The advanced protocol for enzyme immobilization allowed a glucose biosensor to
be produced with good analytical performances.

13.5.4 Towards the biosensors with the best analytical
performance characteristics
The glucose biosensor, except for its highly important practical applications, is con-
sidered as a test to demonstrate the achievements in biosensorics. Indeed, having more
than 40 years of history, glucose biosensors were categorized according to the majority
of the principles available.
To make the most advantageous glucose biosensor, it is important to combine the
best transduction principle with the best immobilization protocol. As mentioned, the
most progressive way to couple the oxidase and the electrode reaction is a low poten-
tial detection of hydrogen peroxide. Among available H 2 O 2 transducers, Prussian blue
is the most advantageous one.
A glucose biosensor was made by immobilization of glucose oxidase over a
Prussian blue-modifi ed electrode (Fig. 13.8). The scheme of biosensor operation
included glucose oxidation by molecular oxygen producing hydrogen peroxide. The
latter is reduced on Prussian blue-modifi ed electrodes producing an analytical signal.
Analytical performances of the glucose biosensor in fl ow-injection mode are as
follows. The biosensor allows detection of glucose down to the 0.1 µ M level. The

Glucose

Nafion

H 2 O 2

Gluc. acid

H 2 O

Oxygen

Prussian blue

Glucose oxidase

FIGURE 13.8 Principal scheme of the Prussian blue-based glucose biosensor.