Biomedical Engineering Reference
In-Depth Information
4.3
Enzyme-Based Electrochemical Biosensors
Biosensors are analytic devices that are capable of providing either qualitative
or quantitative results. Biosensors combine the excellent selectivity of biology
with the processing power of modern microelectronics and optoelectronics to
offer powerful new analytic tools with major applications in medicine, envi-
ronmental diagnostics, and the food and processing industries. This review
covers enzyme-based electrochemical biosensors, particularly amperometric
enzyme sensors for glucose monitoring.
4.3.1
Introduction
The measurement of the blood glucose level is very important for the dia-
gnosis of diabetes mellitus, and many glucose sensors have been developed
[13]. Most glucose sensors are enzyme-based amperometric biosensors. Three
general strategies are used for the electrochemical sensing of glucose, most
of which use immobilized glucose oxidase (GOx), an enzyme that catalyzes
the oxidation of glucose to gluconic acid with the production of hydrogen
peroxide. The first detection scheme measures oxygen consumption; the se-
cond measures the hydrogen peroxide produced by the enzyme reaction; and
a third uses a diffusable or immobilized mediator to transfer the electrons
from GOx to the electrode.
It is easy to construct glucose sensors based on the principle of mea-
suring the consumption of oxygen or the production of hydrogen peroxide
(Fig. 4.17). However, they are disadvantageous in that the signal depends on
the dissolved oxygen concentration. Blood glucose concentration is compara-
tively high, and it is around 5 mM in the hungry healthy human. It reaches
20 mM for diabetic patients, and measurement of the accurate glucose con-
centration by the sensor on the basis of this principle is dicult, since the
oxygen concentration is insucient. Furthermore, a high potential is neces-
sary to reduce oxygen or to oxidize hydrogen peroxide. For example, in the
case of a metal electrode, when 700 mV is applied to a silver/silver chloride
Fig. 4.17.
The rinciple of a conventional electrochemical biosensor
