We have designed, built, and evaluated a microfluidic device that uses deterministic lateral displacement for size-based separation. The device achieves almost 100% purity and recovery in continuously sorting two, four, and six micrometer microspheres. We have applied this highly efficient device to the purification of fungal (Aspergillus) spores that are spherical ( approximately 4 mum diameter) with a narrow size distribution. Such separation directly from culture using unfiltered A. niger suspensions is difficult due to a high level of debris. The device produces a two to three increase in the ratio of spores to debris as measured by light scatter in a flow cytometer. The procedure is feasible at densities up to 4.4x10(6) sporesml. This is one of the first studies to apply microfluidic techniques to spore separations and has demonstrated that a passive separation system could significantly reduce the amount of debris in a suspension of fungal spores with virtually no loss of spore material.

Microfluidic continuous flow filtration methods have the potential for very high size resolution using minimum feature sizes that are larger than the separation size, thereby circumventing the problem of clogging. Branch flow filtration is particularly promising because it has an unlimited dynamic range (ratio of largest passable particle to the smallest separated particle) but suffers from very poor volume throughput because when many branches are used, they cannot be identical if each is to have the same size cut-off. We describe a new iterative approach to the design of branch filtration devices able to overcome this limitation without large dead volumes. This is demonstrated by numerical modelling, fabrication and testing of devices with 20 branches, with dynamic ranges up to 6.9, and high filtration ratios (14-29%) on beads and fungal spores. The filters have a sharp size cutoff (10× depletion for 12% size difference), with large particle rejection equivalent to a 20th order Butterworth low pass filter. The devices are fully scalable, enabling higher throughput and smaller cutoff sizes and they are compatible with ultra low cost fabrication.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.