Table 1.

Summary of gas sensors features based on transduction methods

Sensor types	Mechanism	Features	Refs
Electrochemical	The gases diffused at sensing electrode, then the diffused gas get oxidized or reduced.	-Fast response. High sensitivity and good selectivity. Short operation life.	[328]
Gas chromatography	This method based on separation of gases from the gaseous mixture.	- Expensive. Highly sensitive and excellent selectivity.	[100]
Acoustic	The acoustic detection method is determined by measuring the frequency variation of the acoustic sensor after it absorption/adsorption the gas molecules through the sensing layer.	-Good stability. Good response. Good sensitivity.	[11]
Optical	This detection is based on detection the changes in the optical properties such as colorimetric, reflectance, absorbance, luminescence.	-Long lifetime. Good stability. Good response. Good sensitivity.	[329]
Calorimetric	This detection is based on temperature changes because of the oxidation reaction with the gas molecules	-Less selectivity. Low cost.	[330]