The nanopump, designed in simulations by Haiping Fang and colleagues at the Chinese Academy of Sciences, consists of a short single-walled carbon nanotube. Both ends of the tube are embedded in a graphite sheet and the ensemble is placed in a water reservoir. Three charges – two with fractional charges of 0.5e and one with a charge of 1e, where e is the charge on the electron – are placed asymmetrically about the vertical centre of the nanotube.

In this position, the charges force the dipole moments of water in the nanochannels to point in a certain direction near one of the nanotube ends, so that the liquid can be easily driven along the channel by external fields (see figure). The design is inspired by structures of channels in a cellular membrane that conduct water in and out of the cell.

The new nanopump is radically different to conventional pumps that are driven by electric or magnetic fields and which transport ions or magnetic fluids along a channel. These designs do not work for water because it is charge-neutral and has no magnetic moment.

"We expect the pump could be used to desalinate and purify water, separate chemicals, in sensors and drug delivery," Fang told nanotechweb.org.

The design also works for insulating nanochannels that could be made in the near future, say the researchers. Moreover, it can be extended to semiconductor nanopores, such as armchair or zigzag single-walled nanotubes.

The researchers will now try to further improve the nanotubes' pumping ability in their simulations. "We would also be very happy to cooperate with experimental groups to solve the problems in making a water nanopump that could be used in the lab and in industry," said Fang.

The team, which includes researchers from the University of Manchester, presented its work in Nature Nanotechnology.