Well, it now appears the University of Manchester in England has built 1nm transistors
on graphene. The article is short on details, but it appears to be a ring of carbon atoms surrounding a quantum dot, where the quantum dot is not used for quantum computing or quantum states but rather for regulating the electrical properties. This is still a long way from building a practical IC using graphene. It is, however, a critical step forward. The article mentions other bizare behaviours of graphene but does not go into much detail. This is the smallest transistor produced to date.