Sometimes size DOES matter!
By Kathrin Herbst
Graphene meets DNA – a way semiconductors can go nanoscale.
The world’s latest diode is not made of old fashioned mineral crystals, silicon or germanium, and at only 11 units in size it is tiny, with one unit typically representing 0.34nm. Sound familiar?
Yes, it’s our genes. The smallest rectifier ever was created by scientists at the University of Georgia and Ben-Gurion University of the Negev in Israel. They used 11 paired DNA strands and inserted two small molecules of coralyne into certain positions of the strand. This little change allowed electric current to flow directionally. Making use of single molecules, DNA and other, basic mechanisms of cell biology (or more broadly, synthetic biology) to fashion such miniaturized diodes or other clever components might soon help to push man-made device technology beyond its current limits…
Origami also applies those general principles of life and is still as popular as it was in 6th century Japan and for a good reason. Being not just a matter of folding paper any which way you want, traditional origami art enables the creation of elegant 3D- sculptures by simply folding 2D-sheets. The fundamental geometry at the core of origami can be adapted to approach problems in industrial design. To date, origami-engineering applications have been developed using these smart folding concepts to solve real-life problems across different engineering disciplines and origami folding techniques have been developed for a range of technological applications with great success.
One great success story of origami has been described at NASA’s Jet Propulsion Laboratory where Japanese scientists designed the famous “Miura-ori” solar panel for space deployment. Shrink Dinks desktops (printer-printed light reactive self-folding polymer sheets) as investigated by Michael Dickey from North Carolina State University might be in a far earlier development stage but could reveal similar potential. More recently, even bio-engineers and molecular engineers became inspired by origami strategies. Besides the more practical Origami paper based analytical service (oPAD) developed by Crooks and Liu from the University of Texas (Austin), a cellular origami that utilised actomyosin interactions and actin polymerization to allow living cells to self-fold and produce micro structures were designed by Tokyo’s Kuribayashi-Shigetomi very recently.
Such molecular origami techniques might boost technologies such as drug release, delivery, and cost effective, early disease detection. That said, we might still be decades away from seeing the real value of these innovations in applications around us.
Certainly among the most exciting technologies of origami-inspired design for industrial use is the graphene Kirigami (bendable single-carbon lattice). Graphene conducts electricity and is commonly used in the production of semiconductors or battery components. The material is a hexagonal lattice of carbon atoms arranged as a one-atom-layer sheet about 200 times stronger than steel, but unfortunately also very brittle. In 2015 Blees et al. from Cornell University created a flexible graphene structure using origami design. The Kirigami sheets were found to be thousands of times more flexible than normal graphene and could allow for bendable semiconductors or even wearable batteries (University of Michigan’s Kirigami battery).CAMPAIGNDiagnostics development
But what if size matters?
Some recent attempts at creating new and much smaller semiconductors were aimed at making wearables more comfortable or fit better into narrow spaces. These efforts have been based on molecular engineering, using the biological building block Deoxyribonucleic acid (DNA). DNA is a double-stranded, helical macromolecule which usual function is to encode the genetic information of an organism; these properties have been exploited to manipulate DNA’s ability to fold into 2D and 3D-shapes in a nanoscale range in the so-called DNA origami technique.
DNA as building blocks to can allow for new industrial design
The idea of using DNA as a construction material is perhaps not that new as the principle was already established in the 1980s. However, the technology has evolved significantly since then. Currently, scientists are trying to use DNA’s very small size, base-pairing capabilities and its inherent ability to self-assemble to create nanoscale structures for electronics, resulting in drastically reduced component sizes. The smallest features on chips currently produced are roughly 10 times larger than the diameter of single-stranded DNA – just 1.2 nm. DNA as such does not conduct electricity very well but metal-containing DNA origami structures do.
The future might be in interdisciplinary engineering
In essence, DNA structures can serve as a 3D structural scaffold which supports construction of an integrated circuit on them, thus forming a molecular semiconductor. In collaboration with Robert C Davis and John N Harb at Brigham Young University, Woolley’s team at Brigham Young University published the build of a 3D tube-shaped DNA origami structure that sticks up from common base substrates (e.g. silicon) and can form the bottom layer of a chip. They describe their ultimate goal as attaching gold nanoparticles to tube-like origami structures and to place them at particular sites on a substrate. Linking these gold nanoparticles with semiconductor nanowires would ultimately form a circuit.
Conventional chip fabrication becomes extremely costly when it comes to very small chip dimensions. A technology that is based on self-assembling DNA carries great potential for cost savings. Yet we are only witnessing the onset of interdisciplinary engineering in the 21st century.