Nano toolbox gains carbon cones

Researchers from the University of Louisville and Rensselaer Polytechnic Institute have come up with a useful twist on carbon nanotubes. Their nano pipettes grow thicker at one end to form microscopic cones that have central channels.

Carbon nanotubes are ready-made, strong, electrically useful microscopic tubes that form naturally in soot from sheets of carbon atoms.

Nanopipettes could eventually deliver tiny amounts of fluids under the skin, sense chemicals at very specific locations, form electrodes for retinal stimulation, and be tips for atomic force, scanning tunneling, and near-field scanning optical microscopes.

The researchers found that when they immersed platinum wires in methane/hydrogen plasma, sheets of carbon atoms wound around a central nanotube to make nanotubes whose outer walls tapered from as many as 700 nanometers to only a few nanometers. The nanopipettes were as long as 6,000 nanometers. A red blood cell is 5,000 nanometers in diameter.

The researchers are now working on controlling the length of the pipettes and on growing them on flat substrates with an eye toward growing long, dense arrays of pipettes that could be used for drug delivery. Nano pipettes could be used in commercial products in two years, according to the researchers. The work appeared in the May 14, 2003 issue of Nano Letters.