US Patent 7938969 - Size separation of magnetic nanoparticles

http://www.freepatentsonline.com/7938969.html

Magnetic nanoparticles have usefulness as biological tags and in some memory devices. This patent from Rice University teaches a method of separating magnetic nanoparticles by size. Claim 1 reads:

1. A method for separating magnetic nanoparticles comprising:

providing a sample comprising a plurality of magnetic nanoparticles;

passing the sample through a first magnetic field;

at least partially isolating magnetic nanoparticles of a first nanoparticle size desired;

altering the strength of the first magnetic field to produce a second magnetic field; and

at least partially isolating magnetic nanoparticles of a second nanoparticle size desired.