Carbon-Electrode Dielectrophoresis to Identify Candida strains
Authors: Barnett Emma , Vogel Max , Hammond Carly , Bisbee Cora , Jones Paige , Keck Devin Monroe , Martinez-Duarte Rodrigo 
Published: February 2020

Presented here is the use of 3D carbon microelectrodes in the separation of two different Candida strains using dielectrophoresis. The identification of Candida glabrata from Candida albicans has clinical relevance as front line antibiotics commonly used for Candida albicans, the most likely cause of candidiasis, are not effective to eradicate C. glabrata. Candidiasis occurs when a Candida species infiltrates the bloodstream. It is the most common bloodstream infection in the United States, and represents a significant challenge to the healthcare industry (1). While these yeast species are common inhabitants of the gastrointestinal tract and skin, they have the potential to cause infection in patients with compromised immune systems. These infections are problematic in hospitals, and have been estimated to have a mortality rate of up to 44% in some studies (2). Standard procedures following suspicion of candidiasis is the culturing of a sample for up to 1-2 days in agar followed by further testing to analyze spore formation before the species can be appropriately identified and treated (1). In the meantime, the patient is treated with a cocktail of antibiotics to target the most common pathogens. However, C. glabrata are resistant to commonly used antifungal drugs such as fluconazole (3). Hence, a rapid assay to detect the presence of Candida in a sample and further identifying the strain present can have a drastic impact on the treatment of candidiasis. This will enable timely treatment with the most suitable antibiotic, i.e. amphotericin B for C. glabrata, rather than treating the patient with a cocktail of antibiotics; an approach now leading to resistance in many Candida strains (3).
Here we report the potential of dielectrophoresis to separate strains of Candida. Dielectrophoresis is an electrokinetic method that allows the dielectric properties of cells to be exploited for manipulation, isolation, and separation purposes. This is because targeted cells will display a specific response to a non-uniform electric field varying in frequency and magnitude (4). In our system, we implement the electric field gradient required for DEP using 3D carbon electrodes. When compared to traditional 2D electrodes, the use of 3D electrodes reduces the main distance from any cell flowing in the channel to the nearest electrode, thus resulting in better trapping throughput and efficiency (4). The use of carbon allows for a more robust device since carbon features a wider electrochemical stability than Au and Pt. Initial results show that different Candida strains feature a different DEP response at different frequencies (fig. 1). Using these methods of manipulation, our goal is to use this technique to devise a tool that uses the different response frequencies to separate the strains of Candida present in a sample. This could be useful in a clinical diagnostic setting for determining which strain is present to pinpoint certain interventions that are preferred for the different strains.
Ongoing work is on determining the specific frequency at which one strain, and not the other, shows positive DEP as the basis of isolation. We will trap one strain on the electrode array while eluting the other one. This will allow for cell separation but also enrichment of the targeted species. Once enriched, the population concentration could be determined using optical or electrochemical means. Candidiasis affects thousands of people worldwide due to it’s resistant tendencies. A DEP-based assay to detect the cause of candidiasis will be an important tool in reducing its socioeconomic burden.

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Figure 1