Sorting biomolecules without diffusion

Given a complex biological mixture, scientists frequently need to sort its contents by size or density. Typical methods rely on particle diffusion into different regions of an apparatus. Researchers from Princeton University have come up with a new, deterministic sorting technique that exploits microfluidics. In their device, a laminar fluid carries the biomolecules of interest in a stream through an array of artfully staggered rows of obstacles. Depending on the uniform size and spacing of obstacles in a row, and the staggering from one row to the next, molecules of a certain size will zigzag through the obstacles but, on average, proceed straight with the flow through the array. Larger biomolecules, however, are preferentially carried off at an angle as they traverse the array and separate from the smaller molecules. In initial demonstrations, the researchers have sorted fragments of artificial bacteria chromosomes to within 12% of their molecular weight in 10 minutes, an order of magnitude faster than is possible with conventional methods. (L. R. Huang et al., Science 304, 987, 2004 http://dx.doi.org/10.1126/science.1094567 .)