Size-Based Separation of Microparticles in a Multilayered Microfluidic Device

The current analysis of microbial populations in diverse environments is stymied by the inability to culture the vast majority of microbes in a laboratory setting. Consequently, considerable work is currently underway to identify new microbes based on genetic characterizations, and one limitation is that the majority of sequencing schemes will miss rare populations of microbes as large numbers are pooled for analysis. One approach to overcome this obstacle is to presort the microbes from a heterogeneous field sample based on size, as many microbes live in small clusters, and then analyze the various strains using in situ hybridization. In this paper, a multilayered microfluidic device has been developed for the size-based separation of heterogeneous microbial samples as a first step toward this goal. This device is fabricated using polydimethylsiloxane and soft lithographic techniques. The device includes three successive constrictions with reducing heights and was employed to successfully separate a heterogeneous population of microparticles and field samples obtained from Lake Michigan. The device was found to trap the microparticles and environmental samples with efficiency between 89% and 98% when the particles were larger than the constrictions and 97% for the unknown environmental sample.