Created by a team led by Asst. Prof. Benedetto Marelli and Prof. A. John Hart, the new MIT patch is made from silk fibroin – which is an edible protein extracted from moth cocoons – along with two types of "bioink" polymers. One of these is sensitive to a molecule in E.coli bacteria, while the other is sensitive to pH levels that are typically associated with food spoilage. In both cases, the polymer will change color if the targeted molecule or pH values are present. When the patch is pressed against the surface of a piece of fresh produce, its needles (each measuring about 1.6 mm long by 600 microns wide) will draw in fluids from within that item. This is reportedly a more accurate approach than those which just test the surface of the food, as such surfaces may contain nooks and crannies in which pathogens can hide from sensors.