Sensor Used in E-nose - The Electronic Nose Artificial Olfaction Technology - page 151

• Medium selectivity, i.e., respond to special compounds present in the sample.
• High stability.
• High reproducibility and reliability.
• Short response and recovery time.
• Dynamic and longlasting.
• Easy to calibrate.
• Easily processable data output.
• Small size.

Number of types of sensors are available and used as E-nose sensors for the
analysis of volatile gases, which includes metal oxide semiconductors (MOS),
conducting polymers (CP), chemocapacitors; MOS field effect transistors (MOS-
FET), quartz crystal microbalance (QCM), surface acoustic wave (SAW), and
SPR. The sensors which are used to detect the molecules of chemicals are based on
the measurement principles such as electrical, thermal, optical, and mass changes.

6.5 Biochemical Sensors

A chemical sensor is defined as a device that transforms chemical information,
ranging from the concentration of a specific sample component to total compo-
sition analysis, into an analytically useful signal. Odor molecules based on the
reaction between the odor molecules and the objective sensing materials on the
sensor surface detected by chemical biosensors. These reactions activate a positive
change in physical properties, i.e., mass, volume, or other. This change is con-
verted into an electronic signal by a transducer.
The combination of bio and electrochemistry, solid-state and surface physics,
bioengineering, data processing implies the possibility of a new generation of
highly specific, sensitive, selective, and reliable biochemical sensors.
Different types of transducers are used in chemical sensors: optical, electro-
chemical, heat-sensitive, and mass-sensitive. This transducers principles also work
as biochemical sensor as described in Table 6.2 .

Table 6.2 Principle, measurand and typical examples of biochemical sensor

Principle Measurand Typical sensor

Conduct metric Resistance/conductance Tin oxide gas sensor

Potentiometric Voltage/e.m.f. Ion selective FET for pH

Capacitive Capacitance/charge Polymeric humidity sensor

Amperometric Current Electrochemical cell

Calorimetric Heat/temperature Pellistor gas sensor

Gravimetric Mass Piezoelectric or SAW sensors

Optical Path length/absorption Infra-red detector for Methane gas

Resonant Frequency Surface Plasmon

Fluorescent Intensity Fiber optic