Your posts are always informative. I don't know if this chemical sensors are sold in Nigeria. So many lives have been lost due to Carbon monoxide poisoning here in Nigeria. The use of power generating sets is the major cause of this. The chemical sensor will go a long way to save lives.
The possibilities you mentioned are quite interesting too especially for purifying water a day detecting bombs. Basically more should be done to create chemical sensors that not only warn but also prevent deaths. Peace