by Kurt Kleiner
A three dimensional grid of quantum dots created and held together by genetically-engineered viruses could enable a new generation of computer displays, memories and even nanoscale computer chips.
Angela Belcher and colleagues at the University of Texas at Austin engineered long, threadlike viruses so that their ends would stick to molecules of zinc sulphide and form them into tiny crystals. But the viruses also lined themselves up, creating a structure so regular and strong that a thin plastic-like film was created.
Christopher Ober at Cornell University says the structures formed by the method are much smaller than any circuits that can be created using even advanced optical or electron beam lithography.
Quantum dots are small semiconductor structures that have the ability to trap a single electron, and could form the basis for nanoscale electronic devices. There are a number of ways of creating these - Belcher has previously used engineered bacteria - but the challenge is to form groups of them into a regular structure.
All in order
The researchers tackled the problem by using a rod-like virus that infects and reproduces in bacteria. They created viruses that were about six nanometres in diameter and 880 nm in length. The viruses had a peptide sequence at one end that would bind to zinc sulphide - changing this peptide would mean quantum dots could be made from other materials.
Then they took the viruses and mixed them in a solution containing zinc sulphide. Each virus assembled a nanocrystal of about 20 nm diameter at one end that had the ability to function as a quantum dot. What is more, when the concentration was just right, the viruses all lined up evenly spaced and end to end, similar to the way molecules in a polymer order themselves.
When Belcher allowed the solution to dry on a substrate, she ended up with a thin, transparent film composed entirely of viruses and nanoparticles, with an area of several square centimetres. It was solid enough to handle with forceps without breaking.
At the moment this film cannot do anything. But it could form the basis for new kinds of display screens, for very dense magnetic memory, or even for computer chips far tinier than any that can be created today.
Belcher says that the trick will be in wiring up the quantum dots once you have got them laid out in their grids. She is now experimenting with methods that would cause targeted viruses to let go of their quantum dots, and replace the virus with a conductive filament. In this way, circuits could be designed.
Journal reference: Science (vol 296, p 892)
NewScientist.com news service