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NOVEMBER 2018 I PCB007 MAGAZINE 35 This work follows up on ear- lier research by Strano and his students on developing syn- cells that could gather infor- mation about the chemistry or other properties of their sur- roundings using sensors on their surface and store the in- formation for later retrieval. For example, injecting a swarm of such particles in one end of a pipeline and retrieving them at the other to gain data about conditions inside it. While the new syncells do not yet have as many capabilities as the ear- lier ones—which were assem- bled individually—this work demonstrates a way of easily mass-producing such devices. Apart from the syncells' po- tential uses for industrial or biomedical monitoring, the way the tiny devices are made is innovative and has great potential, according to Liu. "This general procedure of using controlled fracture as a production method can be extended across many length scales," he says, "[It could poten- tially be used with] essentially any 2D materi- als of choice in principle, allowing future re- searchers to tailor these atomically-thin surfac- es into any desired shape or form for applica- tions in other disciplines." According to Liu, this is one of the only ways available right now to produce stand-alone in- tegrated microelectronics on a large scale that can function as independent, free-floating de- vices. Depending on the nature of the electron- ics inside, the devices could be provided with capabilities for movement, detection of vari- ous chemicals or other parameters, and mem- ory storage. There is a wide range of potential new appli- cations for cell-sized robotic devices, says Stra- no, who details many possible uses in a book he co-authored with Shawn Walsh, an expert at Army Research Laboratories, on the subject— Robotic Systems and Autonomous Platforms— which is being published by Elsevier Press. Circles on a graphene sheet where the sheet is draped over an array of round posts, creating stresses that will cause these discs to separate from the sheet. The gray bar across the sheet is liquid being used to lift the discs from the surface. (Source: MIT) As a demonstration, the team "wrote" the letters M, I, and T into a memory array within a syncell, which stores the information as vary- ing levels of electrical conductivity. This infor- mation can then be "read" using an electrical probe, showing that the material can function as a form of electronic memory into which data can be written, read, and erased at will. It can also retain the data without the need for pow- er, allowing information to be collected at a later time. The researchers have demonstrated that the particles are stable over months even when floating in water, which is a harsh sol- vent for electronics, according to Strano. "It opens up a whole new toolkit for micro- fabrication and nanofabrication," he says. Strano's team also included MIT graduate student Jing Fan Yang; postdocs Daichi Ko- zawa, Juyao Dong, and Volodomyr Koman; Youngwoo Son, research affiliate Min Hao Wong; Dartmouth College student Max Sacco- ne; and visiting scholar Song Wang. The work was supported by the Air Force Office of Sci- entific Research, and the Army Research Office through MIT's Institute for Soldier Nanotech- nologies. PCB007