Last year, the US-based group showed that direct contact with SWNTs can deactivate bacteria (see related story - Carbon nanotubes render E. coli inactive) and now the researchers are busy putting their findings to use in the lab.

The team's prototype filter consists of a polymer microporous membrane covered with a thin layer (2–6 µm) of SWNTs. The design allows high-water fluxes and low operating pressures, which will help to keep operating costs down.

Results show that the group's SWNT filter exhibits very high removal of viruses (over 5 log or 99.999%). Furthermore, the SWNT filter not only completely retains E. coli cells, but also renders the bacteria inactive. Tests indicate that only 6% of E. coli cells remained metabolically active on the SWNT enhanced substrate compared with a figure of 70% for an untreated base membrane.

Once again, SEM images reveal a dramatic change in the cell morphology of material in contact with SWNTs. Bacteria captured by the SWNT covered filter are flattened and show signs of severe cell-membrane damage.

So far so good, but what about the possibility of SWNTs breaking free and contaminating the water?

"The carbon nanotubes are deposited onto the feed side of the microporous membrane and are bound together through hydrophobic forces," Elimelech told nanotechweb.org. "No carbon nanotubes have been identified as leaching off the filter, but future development will include immobilization onto a ceramic filter."

By using materials with a high thermal resistance, Elimelech and his colleagues hope to design a reusable filter that can be regenerated by a simple heat treatment.

The researchers published their results in Small.