Graphene is an allotrope of carbon in the form of a two-dimensional, atomic-scale, honey-comb lattice in which one atom forms each vertex. Graphene is the thinnest known material in the universe and the strongest ever measured, which is about 100 times stronger than the strongest steel. Graphene has found wide applications in advanced composite materials, batteries, solar cells, supercapacitors, catalysts, biosensors and drug delivery.