Selective nanofilters created for proteins and DNA

Researchers at the University of California, Davis have developed a new type of nanotechnology-based filter that can separate out mixtures of biological molecules. The technology could be used to build small-scale devices for research in genomics by sorting mixtures of different proteins or DNA molecules.

The filter is said to consist of a polycarbonate membrane etched with pores less than 10 nanometers in size. The pores are lined with a thin layer of gold and then with another layer of oily molecules called thiols. The thiols spontaneously arrange themselves into a membrane one molecule deep, with all the thiol molecules pointing the same way.

Thiols are chains of carbon atoms, with a sulphur atom at one end and an acidic region at the other end. The sulphur allows the thiol to stick to the gold layer. The acidic end can then interact with whatever flows past. The final pores are less than nine nanometers wide.

UC Davis researchers Kyoung-Yong Chun and Pieter Stroeve found that by changing the pH on either side of the membrane, they could open or close the pores to different proteins even of similar size, using a method called electrostatic screening. Existing filters can only effectively separate proteins or biological molecules of different sizes.

‘The switchable technology will be important for transport on the nano-scale, particularly for nano and micro-sensing, analysis on a chip and micro-fluidic devices,’ Stroeve said. Another application could be in controlled drug release, supplying drugs over a period of time when the body needs it, he added.