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Graphene straintronics
CARBON Depositing lithium ions on one face of the carbon monolayer material graphene can endow it with piezoelectric properties, allowing it to generate a voltage when deformed or to deform when a voltage is applied to the material. New research from Stanford University points the way to using graphene as an engineering control material in microelectromechanical systems (MEMS), their nano counterparts, NEMS, and other applications. The physical deformations we can create are directly proportional to the electric field applied. This represents a fundamentally new way to control electronics at the nanoscale, said Mitchell Ong, a post-doctoral researcher in the Materials Computation and Theory Group at Stanford and lead author of the study. The Stanford team, led by Evan Reed, has added a dynamic dimension to straintronics in graphene [ACS Nano (2012) 6(2), 13871394; doi 10.1021/nn204198g]. Piezoelectric graphene could provide an unparalleled degree of electrical, optical or mechanical control for applications ranging from touchscreens to nanoscale transistors, explains Ong. The process of doping breaks physical symmetry and allows the piezoelectric effect to become manifest. We thought the piezoelectric effect would be present, but relatively small. Yet, we were able to achieve piezoelectric levels comparable to some traditional three-dimensional materials, says team leader Evan Reed. It was pretty significant. The teams approach allows them to control where and how much the graphene is deformed by an applied electric field. Moreover, the same doping technique might be applicable to graphenes tubular chemical cousins carbon nanotubes, which have also attracted a great deal of interest for electronics, photonics, sensor, and energy harvesting applications. Conventionally, the piezoelectric effect has been considered an intrinsic property of a given mineral phase, in wurtzite, for instance. The effect arises because the phase has a non-centrosymmetric point group, in other words it is a material without an inversion centre. This new research opens up the concept of nanoscale engineering of this property into twodimensional materials not limited to doped graphene.
Doping one face of a graphene sheet could make the carbon sheets piezoelectric. To arrive at the optimal coating for graphene, the team modeled different approaches to deposition and simulated the piezoelectric effect. The researchers used density functional theory (DFT) to model graphene doped with lithium, hydrogen, potassium, and fluorine, as well as combinations of hydrogen and fluorine and lithium and fluorine on either face of the graphene lattice. Given that some doped forms of graphene have been fabricated, the team is confident that their findings will be demonstrated experimentally.
David Bradley
Nanopills: Just what the Doctor ordered

NANOTECHNOLOGY A multidisciplinary study has developed a new technology that uses nanopills to penetrate and release drugs directly from the interior of cells, which could offer an innovative platform for sustained drug release in advanced protein replacement cell therapies. The researchers produced a new vehicle that undertakes biological activities, allowing for the release of proteins with therapeutic effects, an approach called bacteriainclusion bodies, involving stable insoluble nanoparticles usually present in recombinant bacteria, verifying its tolerance by administering it in vivo. Contrary to the perceived wisdom that protein clusters were merely waste materials or side products, the study, reported in the journal Advanced Materials [Vzquez et al., Adv Mater (2012) doi: 10.1002/adma.201104330], showed that proteins aggregated as bacteria-inclusion bodies retain therapeutic activity, are fully compatible as biologically produced protein materials and also offer unexpectedly high cell penetrability and stability. The team, which have been exploring recombinant protein production in bacteria for many years as a way of engineering therapeutic proteins, allosteric biosensors, and protein nanocages for gene therapy, packaged four proteins containing different functional proteins with direct values in industrial and biomedical applications. As well as demonstrating that inclusion bodies have benefits as therapeutic agents in the form of nanopills, the study presented the formation of inclusion bodies as reversible, that inclusion body proteins are functional, and that inclusion bodies are biocompatible and useful as a substrate of mammalian cell attachment. It is hoped this type of research will offer a better understanding of proteinprotein interactions in protein aggregation, as well as the potential for the controlled biofabrication of a new generation of protein biomaterials with tunable physicochemical and functional properties. As team leader Antoni Vallverde, from the Institute of Biotechnology and Biomedicine at the Universitat Autnoma de Barcelona in Spain, points out, This would specially benefit those diseases for which the production of active protein drugs has been previously discarded due to high production costs. The scientists now hope to examine the further tolerance of nanopills through in vivo administration, as well as how the particles perform in the treatment of specific diseases.
Take 10-9, and call me in the morning. therapeutic effects into experimental nanopills, the inclusion bodies of the bacteria Escherichia coli, before positioning the bacteria together with cell cultures of mammals under similar conditions to those found in real clinical pathologies. These inclusion bodies, which have traditionally been viewed as preventing the commercial production of biodrugs and soluble enzymes and having no biological activity, were identified as indeed containing useful levels of
Laurie Donaldson
MAY 2012 | VOLUME 15 | NUMBER 5
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Nanopills: Just what the Doctor ordered

MAY 2012 | VOLUME 15 | NUMBER 5

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