A sensitive C. elegans chemotaxis assay using microfluidic device generating a linear gradient of chemoeffectors

The chemotactic response of the soil nematode Caenorhabditis elegans has been traditionally studied by observing its crawling movements across a chemical gradient on agar plates. However, agar plates generate a temporally evolving gradient and make it difficult to obtain the reliable chemotactic response of the worms. Previously, we reported that, on a micropost array of agar, C. elegans effectively swim by mechanosensational reflexes, which generate coordinated sinusoidal movements in water. In this paper, we report the development of a microfluidic chemotaxis assay system for C. elegans by combing a micropost array with a microfluidic device, generating a stable linear gradient of chemoeffectors. In the assay system, worms were attracted to 1 nM NaCl, which is six orders of magnitude lower than 1 mM, the known concentration of attraction. Worms were repelled from even 0.001% sodium dodecyl sulfate. Our results suggest that our assay system is useful for studying the chemotactic response of C. elegans to soluble compounds.