Barron and colleagues first demonstrated amplification a few years ago, but it wasn’t very efficient. In a paper published online in June in the journal Nano Letters, they described a combination of the right catalysts and growth conditions that would ensure that every single nanotube would be amplified. Previously they’d assumed these conditions should be identical to the ones used to make the starting batch of nanotubes, but it didn’t work very well. Barron says they have now found the conditions to make amplification work.

The Rice researchers are using the amplification process to accumulate enough pure metallic nanotubes to make a fiber of the type that would be used to make an electrical transmission line. They’ve made long, conductive nanotube fibers in the past using a spinning process also developed at Rice, but they’ve had to use impure nanotubes to make any great length of the material.

Aaron Franklin, a researcher at IBM’s Watson Research Center, says the new study probably doesn’t “reveal the golden ticket for achieving high volumes of metallic-only tubes.” The amplification process is still not producing very large quantities of the material, Franklin notes.

While the Rice group continues to work on amplification, other researchers are exploring alternative ways of making pure nanotubes in quantity. Mark Hersam, a professor of chemistry at Northwestern University, developed what is now one of the most commonly used separation methods. He founded a company called NanoIntegris to sell pure nanotubes. He says ramping up production “is now essentially an industrial optimization exercise.”