- Email: [email protected]
See-through circuitry
NEWS
Measuring currents, one protein at a time BIOMATERIALS Measuring the photo currents in a single, functionalized photosynthetic protein system is now possible thanks to work by researchers in Germany and Israel [Daniel Gerster et al., Nature Nanotechnol (2012) 7, 673-676; doi: 10.1038/nnano.2012.165]. The demonstration that light can drive the electron pump within these proteins points the way to improving our knowledge of how photosynthesis works. The same insights might also be exploited in using these, or related chemical structures, in molecular circuitry that is directly addressable with light. Joachim Reichert, Johannes Barth and Alexander Holleitner of the Technische Universitaet Image courtesy of Christoph Hohmann, NIM. Muenchen and Itai Carmeli of Tel Aviv University have investigated the photosystem-I down the photocurrents produced with equipment reaction center found in plant cell membranes sensitive enough to analyze a single protein in strong and in chloroplasts from cyanobacteria. These units optical fields. underpin the ability of plants, algae and cyanobacteria Their approach involved forming an electrical contact to utilize solar energy to generate chemical energy, with a single molecule that will function in a strong sugar molecules, from carbon dioxide and water. optical field. This method hinged on the self-assembly The first stage in photosynthesis involves light absorption of the photosynthetic proteins and the formation of and the transfer of this energy to produce an electron a covalent bond between a sulfur atom in a mutant flux. This job is carried out by the photosynthetic cysteinyl amino acid residue engineered into the proteins comprising chlorophyll and the carotenoid photosynthetic protein unit and a gold electrode. They complexes. Reichert and colleagues are the first to pin
then used scanning near-field optical microscopy itself having a gold-covered glass tip to probe the behavior of the protein. Photons optically excite the protein through the tetrahedral tip, which simultaneously completes the electrical circuit. The team recorded a photocurrent of about 10 picoamps from the covalently bound single-protein junctions. This, they explain, is in agreement with the known internal electron transfer times of photosystem I. The team has demonstrated not only that it is possible to measure the photocurrent in a single protein molecule but also that such units can be integrated and so allow them to build selectively addressable artificial photovoltaic devices. The proteins retain their photosynthetic capabilities and so represent highly efficient single-molecule electron pumps that might be used to generate power in a nanoscale electrical circuit. “One has to point out here that this experiment has clearly a proof of principle character,” Reichert told Materials Today. “There are plenty of experiments to be done with a set up that allows you to electrically characterize single molecule junctions in strong optical fields,” he says.
David Bradley
See-through circuitry ELECTRONIC MATERIALS For flexible computer memory and a future generation of three-dimensional opto-electronic devices, transparency could be the key to success. Now, a US team has extended its earlier work on electrically selfhealing graphite to make an active, transparent material that is entirely metal free, when used with graphene terminals [Tour et al., Nature Commun (2012) 3, 1101; doi: 10.1038/ncomms2110]. Chemist James Tour and physicist Douglas Natelson of Rice University and colleagues have combined forces in their search for highly transparent, non-volatile resistive memory devices and discovered that silicon oxide itself can be made to switch. Appling a voltage to a thin sheet of silicon oxide on a polymer substrate with either indium tin oxide or graphene terminals, removes oxygen atoms from a 5 nanometer channel forming conductive silicon. A lower voltage regenerates the oxide in a
472
process the team says can be repeated over thousands of cycles. The channel could be considered as being in the “1” or “0” binary state depending on whether it is oxide or native silicon. Current silicon circuitry is based on a 22 nanometer resolution, the Rice work hints that memory circuits might be functional at 5 nm although finding a way to manufacture at that resolution is still a long way off. Moreover, the physical limits of the lithographic technology used to pattern and etch silicon could be a barrier to taking the next step. The Rice team points out that their unit only needs two terminals, which lowers the overall complexity significantly and would allow multiple units to be stacked in 3D arrays. The researchers are also developing so-called crossbar memories that have embedded diodes controlling the “read-write” voltages. “We’ve been developing
NOVEMBER 2012 | VOLUME 15 | NUMBER 11
this slowly to understand the fundamental switching mechanisms,” Tour explains. “This is now transitioning into an applied system that could well be taken up as a future memory system,” he adds. Early applications for these devices might be in extreme environments where radiation levels or temperatures are high, such as in orbit around the Earth for International Space Station applications. The team concludes with the remark that, “As glass is becoming one of the mainstays of building construction materials, and conductive displays are essential in modern handheld devices, to have increased functionality in form-fitting packages is advantageous.” The potential is perhaps obvious for glass display screens on gadgets and buildings with embedded transparent memory modules.
David Bradley
Measuring currents, one protein at a time BIOMATERIALS Measuring the photo currents in a single, functionalized photosynthetic protein system is now possible thanks to work by researchers in Germany and Israel [Daniel Gerster et al., Nature Nanotechnol (2012) 7, 673-676; doi: 10.1038/nnano.2012.165]. The demonstration that light can drive the electron pump within these proteins points the way to improving our knowledge of how photosynthesis works. The same insights might also be exploited in using these, or related chemical structures, in molecular circuitry that is directly addressable with light. Joachim Reichert, Johannes Barth and Alexander Holleitner of the Technische Universitaet Image courtesy of Christoph Hohmann, NIM. Muenchen and Itai Carmeli of Tel Aviv University have investigated the photosystem-I down the photocurrents produced with equipment reaction center found in plant cell membranes sensitive enough to analyze a single protein in strong and in chloroplasts from cyanobacteria. These units optical fields. underpin the ability of plants, algae and cyanobacteria Their approach involved forming an electrical contact to utilize solar energy to generate chemical energy, with a single molecule that will function in a strong sugar molecules, from carbon dioxide and water. optical field. This method hinged on the self-assembly The first stage in photosynthesis involves light absorption of the photosynthetic proteins and the formation of and the transfer of this energy to produce an electron a covalent bond between a sulfur atom in a mutant flux. This job is carried out by the photosynthetic cysteinyl amino acid residue engineered into the proteins comprising chlorophyll and the carotenoid photosynthetic protein unit and a gold electrode. They complexes. Reichert and colleagues are the first to pin
then used scanning near-field optical microscopy itself having a gold-covered glass tip to probe the behavior of the protein. Photons optically excite the protein through the tetrahedral tip, which simultaneously completes the electrical circuit. The team recorded a photocurrent of about 10 picoamps from the covalently bound single-protein junctions. This, they explain, is in agreement with the known internal electron transfer times of photosystem I. The team has demonstrated not only that it is possible to measure the photocurrent in a single protein molecule but also that such units can be integrated and so allow them to build selectively addressable artificial photovoltaic devices. The proteins retain their photosynthetic capabilities and so represent highly efficient single-molecule electron pumps that might be used to generate power in a nanoscale electrical circuit. “One has to point out here that this experiment has clearly a proof of principle character,” Reichert told Materials Today. “There are plenty of experiments to be done with a set up that allows you to electrically characterize single molecule junctions in strong optical fields,” he says.
David Bradley
See-through circuitry ELECTRONIC MATERIALS For flexible computer memory and a future generation of three-dimensional opto-electronic devices, transparency could be the key to success. Now, a US team has extended its earlier work on electrically selfhealing graphite to make an active, transparent material that is entirely metal free, when used with graphene terminals [Tour et al., Nature Commun (2012) 3, 1101; doi: 10.1038/ncomms2110]. Chemist James Tour and physicist Douglas Natelson of Rice University and colleagues have combined forces in their search for highly transparent, non-volatile resistive memory devices and discovered that silicon oxide itself can be made to switch. Appling a voltage to a thin sheet of silicon oxide on a polymer substrate with either indium tin oxide or graphene terminals, removes oxygen atoms from a 5 nanometer channel forming conductive silicon. A lower voltage regenerates the oxide in a
472
process the team says can be repeated over thousands of cycles. The channel could be considered as being in the “1” or “0” binary state depending on whether it is oxide or native silicon. Current silicon circuitry is based on a 22 nanometer resolution, the Rice work hints that memory circuits might be functional at 5 nm although finding a way to manufacture at that resolution is still a long way off. Moreover, the physical limits of the lithographic technology used to pattern and etch silicon could be a barrier to taking the next step. The Rice team points out that their unit only needs two terminals, which lowers the overall complexity significantly and would allow multiple units to be stacked in 3D arrays. The researchers are also developing so-called crossbar memories that have embedded diodes controlling the “read-write” voltages. “We’ve been developing
NOVEMBER 2012 | VOLUME 15 | NUMBER 11
this slowly to understand the fundamental switching mechanisms,” Tour explains. “This is now transitioning into an applied system that could well be taken up as a future memory system,” he adds. Early applications for these devices might be in extreme environments where radiation levels or temperatures are high, such as in orbit around the Earth for International Space Station applications. The team concludes with the remark that, “As glass is becoming one of the mainstays of building construction materials, and conductive displays are essential in modern handheld devices, to have increased functionality in form-fitting packages is advantageous.” The potential is perhaps obvious for glass display screens on gadgets and buildings with embedded transparent memory modules.
David Bradley