Using microfluidic impedance cytometry to measure C. elegans worms and identify their developmental stages

Microfluidic impedance cytometry allows for label-free detection of cells. But it has not yet been used to detect large organisms, such as Caenorhabditis elegans (C. elegans) worms, due to their variable morphology and strong motility. Here, we report on a C. elegans microfluidic impedance cytometry (CeMIC), which enables the electrical impedance measurement of worms when flowing through a straight microchannel and the identification of their developmental stages based on impedance signals. With the optimized configuration of impedance-sensing structures, namely the microchannel and integrated microelectrodes, the influence of undulation and position variation of worms upon the measured impedance can be eliminated. In signal processing, a kernel density estimation method is employed to extract worm-length-related values that can be directly assigned to the developmental stages of worms. The accuracy for impedance-based identification of worm stages can reach 90%. Additionally, the CeMIC device is developed into a simple and automated system for size-based enrichment of worms. Large and small worms from a mixed population are successfully separated to different outlets after identifying their sizes with impedance measurement. Therefore, our CeMIC system provides a promising platform to measure the worm size, identify developmental stages, and prepare size/stage-homogenized populations for C. elegans experiments.