I'm curious about what sort of technology is used for portable chemical sensing and how expensive or portable it is. For instance, I've occasionally been pulled aside by airport security, and they took a swab, wiped it on some piece of luggage and then as I recall (I didn't pay close attention) put it into some device which checked the swab for whatever substance they were interested in. I'm interested in identification of plastics, preferably with a portable inexpensive technology. So I'm curious about what the airports are doing. Is that using an infrared or RF spectrum, or something else? What sorts of inexpensive sensing technologies exist, for any chemical sensing? How sensitive are they, i.e., how small a sample can you work with? I also do a lot of traveling by train. Amtrak's preferred chemical sensing device is called a "dog", usually a Labrador. I suspect those "devices" are a lot quicker, cheaper, and more sensitive than any electronic device, but that's not practical for what I'm thinking about.