In this traditional approach, there is no chemical information being transferred in any way.

We can show that there are differences in the profiles of chemicals that come from the tissue, and these tissue profiles can be used to diagnose a particular disease or determine how far the disease has progressed. We reported in a previous paper, and it is highlighted in the current article, that there are differences in profiles of chemical species from the tissue, indicating a diseased area and also the margin at which that diseased area is separated from the non-diseased area of the tissue.

We really don't know of any explosives that we can't detect.