A Continuous-Flow C. elegans Sorting System with Integrated Optical Fiber Detection and Laminar Flow Switching

Abstract

Sorting of C.elegans genotypes is a routine task in most C.elegans research labs. Conventionally, the worms are sorted manually which is both labor intensive and slow. In recent years microfluidics has become a useful and important tool for biologists to study C.elegans, including sorting. Although they have shown successful sorting results, the immobilization of worms which was adopted in most of these works causes aversive stimulation to the worms and their behavior will potentially be altered when carrying out post-sorting characterizations. In this work, both worm detection and switching are achieved without any intervention of the continuous worm flow. The genotypes of the worms are detected by integrated optical fibers based on their fluorescence, without the need for immobilization. Switching is based on the steering of laminar flow boundaries. A novel design that integrates two control inlets dynamically switches the fluidic flow to desired outlets by changing the relative pressure in the control inlets, which cause the two laminar flow boundaries to steer. Compared to previously reported microfluidic C. elegans sorting devices, sorting in this system is conducted in a continuous flow environment without any immobilization technique or need for multilayer mechanical valves to open and close the outlets. The continuous flow sorter not only increases the throughput but also avoids any kind of invasive or possibly damaging mechanical or chemical stimulus. We have characterized both the detection and the switching accuracy of the sorting device at different flow rates, and efficiencies approaching 100% can be achieved with a high throughput of about 1 worm/s. To confirm that there was no significant damage to C. elegans following sorting, we recovered the sorted worms, finding no differences in behavior and propagation compared to control.