Environ. Sci. Technol. doi:10.1021/es103302t (2011)

Clean water is taken for granted in many countries but more than one billion people worldwide do not have access to water that is safe to drink. The biggest threat is the presence of bacteria that cause diseases such as cholera and giardiasis, so there is a demand for portable systems that can purify water. Theresa Dankovich and Derek Gray of McGill University have now shown that paper impregnated with silver nanoparticles can kill bacteria in water that percolates through it.

Dankovich and Gray immersed sheets of blotting paper in silver nitrate solution, and then placed them in aqueous sodium borohydride to form silver nanoparticles that had an average diameter of 7.1 nm. Model bacterial solutions were then passed through the paper and the effluent water was analysed for bacterial activity.

The McGill researchers found that the nanoparticles killed most of the E. coli and E. faecalis bacteria in the water. Moreover, the silver nanoparticles remained attached to fibres in the paper and did not contaminate the water. The large pores in the blotting paper also allow for the rapid flow of water though the system under the force of gravity without the use of pressure or suction.