"Assembling viral nanotemplates in a spatially and orientationally selective way has been one of the most challenging tasks in developing nanoscale devices," James Culver of the University of Maryland told nanotechweb.org. "Unlike other previous virus-assembly approaches, our technique harnesses the virus's elegant evolutionary adaptation and its own genetic information to assemble it onto programmed areas."

Viruses typically consist of RNA molecules inside a protein coat. In this study, the team used the tobacco mosaic virus, which is a filamentous plant virus consisting of a single strand of RNA inside an 18 × 300 nm rod-like virion.

Culver and colleagues genetically modified the virus, attaching cysteine residues to the virion surface. This provided a useful link for coupling inorganic and organic compounds to the virus, through the cysteine molecules' accessible thiol groups. In this study, the researchers attached molecules of the fluorescent dye Texas Red to enable fluorescence microscopy.

Next the team partially unravelled the viral RNA using a mild alkaline treatment and centrifugation to mimic conditions inside a cell and trigger disassembly of the virus. This revealed the 5' end of the virus genome.

The capture surface for the virus consisted of a gold pattern fabricated on a silicon-oxide wafer by photolithography. The pattern contained two electrically independent electrodes. The team deposited the aminopolysaccharide chitosan onto one electrode by applying a negative bias to it. Next the researchers tethered probe DNA complementary to the 5' end of the virus RNA to the chitosan's primary amines.

Introducing the modified virion particles to the substrate caused the exposed 5' RNA of the virions to attach to the probe DNA on the chitosan layer by a DNA hybridization process.

"One of the natural next steps would be to develop nanoscale array biosensors based on individual viruses assembled on conductive substrates in a highly oriented manner," said Culver. "We are exploring the possibility of integrating our technique at the systems level to develop next generation nanodevices through collaboration within the extensive Maryland Center for Integrated Nano Science and Engineering (MCINSE) network."

The researchers reported their work in Nano Letters.