Biological nanopores can rapidly transport selected ions and molecules through membranes. Aquaporins, for example, transport water at extremely high rates and can also desalinate. These proteins contain channels that are just 0.3 nm wide, which forces the water molecules to pass through in a single file.
A team of researchers led by Aleksandr Noy has now made the first artificial nanopore system that is not only better than aquaporin at filtering water but which can also filter out specific ions as well as biological ion channels can. The new membrane is made of carbon nanotubes (CNTs) that are 10 nm long and 0.8 nm wide embedded in a lipid bilayer. Again, the nanotubes are narrow enough to squeeze water molecules so that they pass through in 1D single file.
Testing out different CNT widths
The researchers, reporting their work in Science, obtained their results by testing out nanotubes of different widths to find out which were the best at filtering water. “We did this by embedding the tubes in lipid vesicle walls, applying osmotic pressure to the vesicles and then measuring how fast they shrunk as water flowed out of them through the ‘nanotube porins’,” explains team member and co-first author of the study Rama Tunuguntla.
The researchers found that nanotubes with a diameter of 0.8 nm are six times more efficient at filtering water than aquaporins. The flux through these tubes is also 10 times greater than those through 1.5 nm-sized ones.
