Biomedical Engineering Reference
In-Depth Information
Gas permeable
membrane
Oxygen electrode
O
2
Buffer
solution
O
2
NO
2
Immobilized
bacteria
FIGURE 10.35
Principle of an NO
2
microbial-type biosensor.
NO
2
gas diffuses through the gas-permeable membrane, it is oxidized by the
Nitrobacter sp.
bacteria as follows:
Nitrosomonas sp
:
2NO
3
Similar to an ammonia biosensor, the consumption of O
2
around the membrane is deter-
mined by an electrochemical oxygen electrode.
The use of microbial cells in electrochemical sensors offers several advantages over
enzyme-based electrodes, the principal one being the increased electrode lifetime to several
weeks. On the other hand, microbial sensors may be less favorable compared with enzyme
electrodes with respect to specificity and response time.
2NO
2
รพ
O
2
!
10.6 OPTICAL SENSORS
Optical sensors play an important role in the development of highly sensitive and selec-
tive methods for biochemical analysis. The fundamental principle that is employed is based
on the change in optical properties of a biological or physical medium. The change pro-
duced can be the result of physical perturbations or intrinsic changes in absorbance, reflec-
tance, scattering, fluorescence, polarization, or refractive index of the biological medium.
10.6.1 Optical Fibers
Optical fibers can be used to transmit light from one location to another with minimal
attenuation and without any transport of heat from the light source. Therefore, they are
used in a whole range of miniature sensors for biomedical applications. Optical fibers
are small, flexible, and intrinsically immune to electromagnetic and radio frequency inter-
ferences. They can produce an instantaneous response to subtle changes in the micro-
environments that surround their optical surface. Therefore, optical fibers permit in vivo
measurements in small blood vessels or in delicate tissues such as the brain.
