"Gene expression can apparently occur within nanofibre-interfaced cells from plasmid DNA that is physically bound to nanofibres," Tim McKnight of Oak Ridge National Laboratory told nanotechweb.org. "This provides a new approach to genetic manipulation, where genes can be introduced and expressed within cells with a high level of control afforded by their immobilization upon the nanofibre scaffolding."

The team grew arrays of vertically aligned carbon nanofibres from 500 nm diameter dots of nickel catalyst on n-type silicon wafers, using plasma-enhanced chemical vapour deposition. The fibres, which were spaced roughly 5 µm apart, were typically 6-10 µm long with base diameters of about 1 µm and tip diameters of 20-50 nm. After making the fibres, the scientists cleaved the wafers into 3 mm square chips.

"Carbon nanofibres can be synthesized at precise locations upon a substrate, can be grown many microns long, and feature sharp, nano-dimensioned tips," added McKnight. "This, along with their vertical orientation upon a substrate, makes them particularly attractive as multi-element cellular scale probes or as a parallel embodiment of traditional single-point micro-injection systems."

McKnight and colleagues surface-modified the nanofibre arrays with plasmid DNA containing an enhanced green fluorescent protein gene. They either spotted the plasmid DNA onto the chips or covalently tethered it to the nanofibres by exposing the fibres to an oxygen plasma, creating carboxylic acid groups that were then used to react and bind with DNA.

Then the researchers centrifuged cloned Chinese hamster ovary cells onto the chips, a process that impaled some of the cells onto the fibres. In some cases they also pressed the chip to encourage fibre penetration into the cells. Finally, the team incubated the chips to grow the cells. Tracking the production of the green fluorescent protein by the cells indicated whether the take-up of the genetic material had been successful.

"This approach could become an effective material delivery tool for routine laboratory use such as the demonstrated genetic manipulation of cells or for exploration of the activity of pharmaceuticals upon cell populations," said McKnight. "Ultimately, longer versions of these structures may provide for clinically-oriented applications such as transdermal drug and gene delivery techniques."

The scientists say their results also show that nanofibre-based devices can be integrated with cellular matrices and remain interfaced intracellularly to them for relatively long periods. "This opens up applications including diagnostic probing of tissue and carbon-nanofibre-based architectures for whole-cell and tissue-based biosensors," added McKnight.

Now, the researchers are investigating using the carbon-nanofibre devices for highly resolved molecular imaging within cells, as well as collaborating with John Cairney of the Institute of Paper Science and Technology to "augment his toolset for the genetic manipulation of loblolly pine, an important wood pulp species." The group also works with the University of Tennessee's Center for Environmental Biotechnology to apply nanofibre techniques to microbial applications. And the scientists are seeking funding to "explore the potential of these techniques as a transdermal drug or gene delivery tool."

The researchers reported their work in Nanotechnology.