Microfluidic Devices for Characterizing the Viability of Cryptosporidia Oocysts by Dielectrophoresis

Cryptosporidium parvum is a dangerous parasitic organism that attacks the small intestine of infected
individuals. This water born pathogen causes the severe intestinal disease cryptosporidiosis, which has no direct
treatment and can often prove fatal to immunocompromised individuals. While its viability is modified by heat
treatment, Cryptosporidia oocysts have proven to be significantly resistant to chlorine-based disinfectants. It is
necessary to research more effective disinfecting agents that can be easily and safely dispersed under these
circumstances.
The search for such an agent would be aided by the availability of a fast, inexpensive, and reliable method
for characterizing the viability of Cryptosporidia oocysts. Towards this, we investigate microfluidic device designs
utilizing the electrokinetic phenomena of dielectrophoresis. Dielectrophoresis, or DEP, is on the translation of a
polarized particle under non-uniform AC electric field. The direction of this force is caused by differences in the
Maxwell-Wagner polarization of the particle and its surrounding fluidic medium as described by the frequency
dependent Clausius Mossotti factor. By analyzing differences in the direction of the DEP force at specific AC field
frequencies, difference between two particles can be discerned. In the case of Cryptosporidia oocysts, we
hypothesize that these discernable differences include modifications to the viability of the parasites, including
changes to their oocyst wall and cytoplasm by disinfecting agents.
In this paper we will optimize microfluidic device designs for dielectrophoretic characterization of the
modifications to viability of the oocysts after disinfection treatment. Through this, several design considerations for
microfluidic devices utilizing this phenomenon will be highlighted. We will also analyze the design, fabrication, and
experimental operation of three microfluidic devices that utilize DEP as a detection method for Cryptosporidium
viability. Three device designs, including a set of quadra-pole electrodes, the diamond post constriction device and
the single channel constriction device were utilized.