Electrotaxis

The Caenorhabditis elegans (C. elegans) nematode is used as a model for a wide range of research studies in disciplines as medicine or biotechnology. Some of the successful applications are the models of human disorders and diseases such as obesity, hypertension or neurodegeneration (Huntington’s Disease or Parkinson’s Disease) [2][3]. Researchers have obtain C. elegans mutants that are a valuable model for the study of these diseases and for the discover of new drugs that can inhibit the effects [1].

A motility study can provide enough information to decide when a drug is producing the desired results. These studies analize the movement of the nematode focusing on variables. Apart of mechanical stimulus as the ones produced with pneumatic actuators, nematodes react to different external stimulus sources. Light, temperature, electricity, magnetism or chemicals exposure cause different attraction (food, electricity) or repulsion (high temperature, UV light) reactions. This reaction can be slow (chemicals and food) or, in some instances, fatal (UV light, temperature). Furthermore, models are affected of the stress level of the subject.

Along with microfluidics there is a close related handling technology that has appeared in the last years: the manipulation of the nematodes through the electric field. This technology is called electrotaxis and can be used as a stimulus to control the nematodes movement in a microfluidic device without the need of making the fluid flow. This stimulus causes no harm to the nematodes and keeps their life expectancy and fertility intact [4].

Only a low conductivity of the medium is required, low enough not to affect C. elegans models (M9 medium). Furthermore, the direction of the movement can be changed by inverting the voltage polarity [4].

Figure 1: Electrotaxis Microfluidic Chip

This technique can also be applied on Agar gel medium used in Petri dishes for some model studies. It requires a higher voltage, similar to the electrophoresis technique. The results shows that the movement is still from the positive to the negative electrode but in this case, being a surface, the direction is not the only variable being used but also the angle of the movement. This angle increases as the current does [3].

Figure 2: Electrotaxis effect on Agar gel  open surface [3]

References

[1]        L. P. O’Reilly, C. J. Luke, D. H. Perlmutter, G. A. Silverman, and S. C. Pak, “C. elegans in high-throughput drug discovery,” Adv. Drug Deliv. Rev., vol. 0, pp. 247–253, Apr. 2014.

[2]        A. K. Corsi, “A Biochemist’s Guide to C. elegans,” Anal. Biochem., vol. 359, no. 1, pp. 1–17, Dec. 2006.

[3]        C. Voisine, H. Varma, N. Walker, E. A. Bates, B. R. Stockwell, and A. C. Hart, “Identification of Potential Therapeutic Drugs for Huntington’s Disease using Caenorhabditis elegans,” PLoS One, vol. 2, no. 6, pp. 1–8, 2007.

[4]        P. Rezai, A. Siddiqui, P. R. Selvaganapathy, and B. P. Gupta, “Electrotaxis of Caenorhabditis elegans in a microfluidic environment,” Lab Chip, vol. 10, no. 2, pp. 220–226, 2010.