This isn't going to be easy. I wonder if there's a way to develop a really cheap portable sensor similar to a fire alarm. I've been working on a project that detects (specifically) marijuana smoke and alarms accordingly.
The trick is to make it cheap enough.
They have portable explosives monitors, but they are max expensive. The ones I priced at work were in the 30-32 thousand dollar range.
If you can make one cheap and accurate, the world is yours. Oh, and it needs to detect everything..LOL