Biomolecule separation by steric hindrance using nanofluidic filters

Micro/nanofluidics technologies can be used to solve toughest challenges in the biomolecule analysis. It is now possible to fabricate nanofluidic channels with the dimension of 30-500 nm, and these nanofluidic structures have been formerly used to separate large DNA molecules where molecular dimension is larger than the nanofluidic filter gap size. In this work, we demonstrate separation of biomolecules (DNA and proteins) that are smaller than the nanofluidic filter gap size. This is possible due to the steric hindrance effect of the biomolecules; the entropy of biomolecules has to be decreased for the molecules to enter the nanofluidic filter, which leads to the free energy barrier for the molecular transport. Double stranded DNA molecules as small as 100 bp approximately 34 nm extended length), as well as SDS-coated proteins have been separated in a nanofluidic channel that has the filter gap thickness between 60-120 nm. This result clearly shows the potential of using nanofluidic filters as a sieving medium for smaller biomolecules such as proteins. Compared with traditional random nanoporous materials such as gel or polymer monolith, nanofluidic channels can be made precisely to have a pre-determined 'pore' size and shape, which allows characterization and optimization of biomolecule separation process.