Farnoosh Ostadakbari - School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran
Hamid Rashedi - School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran.
Fatemeh Yazdian - Department of Life Science engineering, Faculty of new sciences and Technologies, University ofTehran, Tehran, Iran
Meisam Omidi - School of Advanced Technologies in Medicine, Shahid Beheshti University of Medical Sciences,Tehran, Iran

The detection and measurement of gaseous components such as odours, toxic and combustible gases with high sensitivity and selectivity in different gaseous environments are required in many different areas. The application of gas phase sensing has a various range from sensingtoxic gases in the air to analysis of the human expiratory air which would provide a non-invasive and convenient method of diagnosis and monitoring disease states with no harm or danger for the person being tested. There are many methods to sense the specific compounds in different gaseous methods and most of them are accompanied with an immobilized enzyme as the main core of detecting process in a biosensor. Today, biosensors utilizing immobilized enzymes are commercially available for carbohydrates, urea, uric acid, alcohol, amino acids and many other substances but there is still efforts for developing biosniffers with immobilized enzymes to sense different substances. In this research, the different methods of developing gas phase biosensors with immobilized enzymes for sensing different substances is studied. Moreover, it is tried to describe the different mechanisms of sensing in biosniffers and in the end, the different methods of designing and developing a biosniffer with immobilized enzyme are studied