Carbon-Electrode Dielectrophoresis to Concentrate Trypanosoma Brucei
Authors: Gullette Emily , Hammer Meredith , Heustess Mary Grace , Mills Allison , Stuart Callie , Islam Monsur , Martinez-Duarte Rodrigo 
Published: February 2020

Trypanosoma brucei (T. brucei) is a parasite that causes human African Trypanosomiasis (HAT), commonly known as sleeping sickness. HAT is spread via bite from a Tsetse fly or congenitally, affecting an estimated 60 million people in Sub-Saharan Africa (Chappuis et al., 2005). This translates to a disease burden of 1.78 million disability-adjusted life years (DALY) (Fèvre et al., 2008). Depending on which parasite strain is contracted, T. b. gambiense or T. b. rhodesiense, patients can live 6-7 years or die within 6 months of infection (Centers for Disease Control and Prevention, 2012). Analysis of cerebrospinal fluid and lymph nodes are conclusive diagnostic tests, but are unaffordable and inaccessible in rural, impoverished areas. In these cases, the most relevant form of screening for HAT is the Card Agglutination Trypanosomiasis Test (CATT) (Chappius et al., 2004). This serological test is inexpensive, fast, portable, easy to use, and easy to read. However, current CATTs are limited in sensitivity and specificity: it can only identify T. b. gambiense and produces false positives for other diseases like schistosomiasis and malaria in 5-20% of readings (Inojosa, 2006). The tests also must be stored at low temperatures, which may be a logistical challenge in rural Africa. Hence, there is a need for a test with improved specificity, sensitivity, and that is easily stored while retaining the low cost advantage of the CATT.

We propose Dielectrophoresis (DEP) as a rapid way to agglutinate targeted T. brucei strains. DEP is an electric-field technique that can induce motion on only selected targets, which will increase the specificity of the test. We use DEP to rapidly segregate T. brucei from its surroundings and agglutinate it on specific spots to facilitate its detection. To this end, we use microelectrodes made of either titanium or carbon. In particular, we postulate the use of carbon electrodes to enable DEP of T. brucei and thus inexpensive, rapid and specific agglutination assays.

The experimental setup includes a microfluidics chip featuring multiple rows of intercalated carbon or titanium electrodes (Martinez-Duarte, 2011). Experimental samples of the animal strain T. brucei brucei were pipetted onto a single electrode array, which was polarized using sinusoidal signals with frequencies between 1kHz to 10 MHz at 1-10 Vpp. The array was monitored to characterize the movement of the parasite around the electrodes. Images taken of the experiments were analyzed to assess the velocity of attachment to the electrode array.

Our initial results with both titanium and carbon electrode arrays showed parasite attachment in the range 750 kHz to 2 MHz. By implementing numerical modeling of the electric field of the device, the electric field gradient was simulated as strongest along the curve of the semicircle. This simulation corresponds to the observed location of attraction.

Ongoing work is to further characterize specificity of T. brucei movement and to investigate new carbon electrode geometries that will increase the speed of parasitic attachment. Our goal is to eventually create a DEP device with an operational protocol similar to that currently used. We aim to create an inexpensive DEP device that only require batteries for operation.

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