Biomedical Engineering Reference
In-Depth Information
substance adsorbs the free electrons and its conductivity changes. As a result, the
change of resistance in the electrical circuit is registered.
Advantages:
• Small size sensors.
• Robust.
• Quite good sensitivity.
• Very low cost.
• Electronic simplicity.
• Long-lasting life to operate.
• Easily fabricated.
• Short response time to analytes.
Disadvantages:
• Sensitivity is affected by humidity and poisoning materials.
• Sensor poisoning, e.g., by sulfur compounds, etc.
• Slow baseline recovery when compounds with high molecular weight are
analyzed.
• Their high-working temperature makes them inappropriate in environments
containing flammable chemicals.
• Poor specificity and selectivity.
• Sensor drift mainly caused by sensitivity loss.
• Signal analysis is difficult due to sensor signal is generally not linear.
• High power level is needed to run the sensors.
Application:
• Detection of gas leakage.
• Detection of combustible and toxic gases.
• Detection of VOC of different foodstuffs such as coffee, milk, strawberry, juice,
meat, etc.
2. Conducting Polymers
Polymers (plastics) are identified as good insulating properties and most used
materials in the modern world. CP are polymer materials with metallic and
semiconductor characteristics, a combination of properties not exhibited by any
other known material. The presence of conjugated double bonds along the back-
bone of the polymer is the key property of a conductive polymer. Also note that the
bonds between the carbon atoms are alternately single and double. For example,
the structure of polyacetylene is shown in Fig. 6.13 .
Organic polymers are much different and can report a wide variety of function-
alities to sensors. The molecular interaction capabilities of a polymer can be selec-
tively modified by incorporating different counter ions during polymer preparation or
by attaching functional groups to the polymer backbone. A different advantage of CP
is that they operate at ambient temperatures. The sensors can detect odors at
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