mit chemists have devised an inexpensive, portable sensor that can detect gases emitted by rotting meat, allowing consumers to determine whether the meat in their grocery store or refrigerator is safe to eat.the sensor, which consists of chemically modified carbon nanotubes, could be deployed in &ldquosmart packaging&rdquo that would offer much more accurate safety information than the expiration date on the package.in this case, the researchers modified the carbon nanotubes with metalcontaining compounds called metalloporphyrins, which contain a central metal atom bound to several nitrogencontaining rings.hemoglobin, which carries oxygen in the blood, is a metalloporphyrin with iron as the central atom.the researchers tested the sensor on four types of meat pork, chicken, cod, and salmon. they found that when refrigerated, all four types stayed fresh over four days. left unrefrigerated, the samples all decayed, but at varying rates. 
