Researchers from University of Wisconsin (with support from DARPA) developed new 4-atom thick graphene-based sensors that are so thin to be virtually transparent - which allows the sensors to perform both electrical and optical brain measurements at the same time.The graphene-based contacts are used to measure and also stimulate neural tissue. These kinds of sensors could provide new insights into relationships between brain structure and function, and how these evolve by injury or disease.The sensors are made from graphene deposited on a flexible substrate.