It’s a credit to scientists in general that they will always admit when nature has outdone them — usually millions or billions of years ago. It’s the basis for biomimetic engineering, and this is no exception. A certain type of butterfly wing has been shown to be extremely efficient and effective at both detecting certain chemicals and showing a response to them — far better than technologies we’ve developed. And this isn’t the first time that’s happened; it seems butterflies have it pretty much figured out.
Scientists at GE (funded by a few million from DARPA) are planning on making tiny sensors that would light up in the presence of various dangerous chemicals, and I see no reason why they couldn’t be woven right into your coat.