Sieve separates on nanometer scale

A molecular sieve fine enough to separate molecules differing in size by a few nanometers has been developed by a research team from Tohoku University in Japan. The sieve is fabricated from a thin film of aluminium oxide supporting an array of silica columns erected in holes that measure 200nm in diameter in the film. The columns block the holes in the film, but have openings themselves to allow the passage of molecules. Depending on the substances being separated, the diameter of the holes in the columns can be adjusted in the 2-10nm range. In one experiment the membrane construct was fabricated with openings of 3.4nm diameter, and separated vitamin B12 with a 2.4nm diameter from myoglobin with a 4nm diameter. Conventional molecular sieves cannot separate out substances so close in size.