MIT system distinguishes same-size molecules

One way of carrying out such separation is by using nanofilters - materials with holes of a precisely controlled diameter - to allow molecules up to that size to pass through while blocking any that are larger.

But a new system devised by a team of researchers at MIT could add an important new capability, namely a way to selectively filter out molecules of the same size that have different chemical properties.

’People usually think of size as being the defining factor, but by making the pores in the filter small enough so that there is a significant chemical interaction between the pore walls and the molecules passing through them, it becomes possible to discriminate according to other characteristics,’ said Karen Gleason, an MIT professor of chemical engineering and associate dean of engineering for research.

In this case, the selection was based on the molecules’ affinity for water. Because the walls of the pores were hydrophobic (water repelling), other hydrophobic molecules were more easily drawn to the pores and propelled through them than other, less hydrophobic molecules.