Scientists have created the world's thinnest balloon, made of a single layer of carbon just one atom thick.The fabric that the balloon is made of is leakproof to even the tiniest airborne molecules. It could find use in "aquariums" smaller than a red blood cell, through which scientists could peer at molecules, researchers suggested.The balloon is made of graphite, as found in pencils, which is made of atom-thin sheets of carbon stacked on top of each other known. The sheets are known as graphene.Graphene is highly electrically conductive, and scientists are feverishly researching whether it could find use in advanced circuitry and other devices."We were studying little graphene trampolines, and by complete accident, we made a graphene sheet over a hole. Then we started studying it, and saw that it was trapping gas inside," said researcher Paul McEuen, a physicist at Cornell University in Ithaca, N.Y.By experimenting further with bubbles made of graphene, McEuen and his colleagues found the membranes were impermeable to even the smallest gas molecules, including helium."It's amazing that something only an atom thick can be an impenetrable barrier. You can have gas on one side and vacuum or liquid on the other, and with a wall only one atom thick, nothing would go through it," McEuen told LiveScience.