Samir Iqbal and co-workers have recently come up with a novel approach that provides precise control of the nanopore size as well as the charge on the pore walls. Iqbal, an electrical engineering assistant professor at the University of Texas at Arlington, US, and his graduate student Waseem Asghar have worked in close collaboration with chemistry professor Richard Timmons to create a method that uses pulsed plasma polymeric films to define the size as well as biochemical behaviour of the pores. Controlling the charges on the pore-walls is a big step forwards towards DNA-sequencing.

"We developed a home-built plasma reactor system, which used methacrylic acid monomer to deposit PPPF films inside the nanopore," explained Iqbal, who works in the University's Nano-Bio Lab, part of the Nanotechnology Research and Teaching Facility. "Essentially we can deposit any monomer and provide specific charges on the pore walls."

The chemical composition of the pore-walls plays an important role in controlling the translocation velocity of DNA and other molecules of interest.

Versatile process

The method uses controlled deposition of a polymer film to reduce the diameter of the nanopore and define the surface chemistry of the structure – walls can be made hydrophobic, hydrophilic, negatively or positively charged by just changing the monomer used.

"The duty cycle is key to controlling polymer cross-linking and the density of the surface functional groups," added Asghar, who is in third year of his doctoral studies. "It's defined in terms of the plasma on/off ratio."

The polymeric deposition process itself opens up new ways to improve the performance of biosensors.

Full details can be found in the journal Nanotechnology.