(65f) Characterizing Silver Nanoparticle-Induced Modifications to the Dielectric Response of Cryptosporidia Oocysts

Water-borne pathogens such as Cryptosporidium parvum and Giardia lamblia cause high rates of gastro-intestinal infections in the developing world, as well as in the US [1],[2]. These oocyst forming pathogens are highly resistant to traditional de-activation methodologies, such as size-exclusion filters and chlorine treatments [3]. While the infection is self-limiting in immune-competent individuals, it can be life-threatening in immune-compromised individuals, such as, people infected with the human immunodeficiency virus (HIV), where it can lead to fatalities [4]. Hence, early detection and de-activation of these water-borne pathogens at ultra-low concentration levels is a major healthcare priority. However, the lack of diagnostic technologies for rapid and highly-sensitive screening of oocyst modifications upon contact with key disinfectants has largely limited the development of de-activation methodologies for these pathogens. Immuno-fluorescence methods cannot distinguish between different species of the pathogens and cannot effectively discern infectivity. Infectivity assessment methods based on measurement of oocyst infectivity within an animal model require a rather high concentration of oocysts (~10⁶oocysts/mL), and involve multiple filtration and concentration steps that do not easily allow for routine and quantitative assessment of the relative effectiveness of each disinfectant [5]. Dielectric spectral methods can distinguish speciation of the oocysts based on fingerprints in the frequency response [6], which can be correlated to animal infectivity models to obtain highly sensitive information on modifications to oocyst infectivity. Herein, under a non-uniform AC field, oocysts were polarized to experience negative dielectrophoresis (pushed away from high field region) at low frequencies (10-100 kHz) where the capacitor due to the oocyst wall determines the dielectric spectra, while at higher frequencies (>200 kHz) where the capacitor becomes conducting, the oocyst cytoplasm determines the dielectric spectra. Modification of the oocyst by disinfectants was found to affect the oocyst cytoplasm to cause it to become less polarizable. Hence, while a functional cytoplasm exhibits a strong degree of positive dielectrophoresis, successively less functional oocysts show weaker degrees of positive dielectrophoresis. To enhance the dynamic range for quantification of positive dielectrophoresis, we utilize constriction devices [7], so that the oocysts are trapped at the constriction tips under positive dielectrophoresis. In this manner, we report on the modification of the dielectrophoretic trapping force on the oocyst after various disinfectant treatments through tracking velocity profiles of the oocyst towards the constriction tip.

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[6] ] C. Dalton, A.D. Goater, J.P.H. Burt, H.V. Smith, “Analysis of parasites by electrorotation”, Journal of Applied Microbiology (2004), 96, 24–32.

[7] Swami, N.; Chou, C.-F.; Ramamurthy, V.; Chaurey, V. Enhancing DNA hybridization kinetics through constriction-based. Lab on a Chip 2009, 9, 3212–3220