how to make smell sensor?

Smell can be used to detect and prevent crimes. Dogs are used to find dead bodies, detect drugs or explosives and can even identify people by their smell. Scientists and engineers are working on machines that can sense smell and so can be used at airports to detect explosives or drugs or to identify people before letting them into a building.
It would be greatfull if we can invent smell sensor ......do anyone would like to share the idea how to create this this sensors..........
-kumar

Smell sensors already exist, such as flammable gas sensors, smoke sensors and perhaps a few others.
It may be some time yet before we see replacement dog smell sensors :wink: