US researchers have developed new nanomaterials that could help solve the age-old public health problem of filtering bacteria from drinking water.

Working with a special kind of polymer called a block copolymer, the researchers at the University of Buffalo have synthesised a nanomembrane containing pores about 55 nanometres in diameter - large enough for water to slip through easily but too small to trap and block bacteria.

Water molecules and bacteria are both measured in nanometres, a unit of length about 100,000 times thinner than the width of a human hair.

To the naked eye, both water molecules and germs are invisible. But at the microscopic level, the two actually differ greatly in size.

A single water molecule is less than a nanometre wide, while some of the most diminutive bacteria are a couple hundred.

"The pore size is the largest anyone has achieved so far using block co-polymers, which possess special properties that ensure pores are evenly spaced," said Javid Rzayev, the Buffalo chemist who led the study with graduate student Justin Bolton.

"What our research team was able to accomplish was to expand the range of available pores to 50 nanometres in diameter, which was previously unattainable by block-copolymer-based methods," he said.

"These materials present new opportunities for use as filtration membranes," he added.

The findings were published online on January 31 in Nano Letters and will appear in the journal's print edition later this year.