A microfluidic diode for sorting and immobilization of Caenorhabditis elegans

Caenorhabditis elegans (C. elegans) is a powerful model organism extensively used in studies of human aging and diseases. Despite the numerous advantages of C. elegans as a model system, two biological characteristics may introduce complexity and variability to most studies: 1. it exhibits different biological features, composition and behaviors at different developmental stages; 2. it has very high mobility. Therefore, synchronization and immobilization of worm populations are often required. Conventionally, these processes are implemented through manual and chemical methods, which can be laborious, time-consuming and of low-throughput. Here we demonstrate a microfluidic design capable of simultaneously sorting worms by size at a throughput of 97±4 worms per minute, and allowing for worm collection or immobilization for further investigations. The key component, a microfluidic diode structure, comprises a curved head and a straight tail, which facilitates worms to enter from the curved end but prevents them from translocating from the straight side. This design remarkably enhances the efficiency and accuracy of worm sorting at relatively low flow rates, and hence provides a practical approach to sort worms even with the presence of egg clusters and debris. In addition, we show that well-sorted worms could be immobilized, kept alive and identically orientated, which could facilitate many C. elegans-based studies.