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Genetic Identification of Malaria with Dielectrophoresis on Nano-Gentic Beads

Zachary R. Gagnon1, Satyajyoti Senapati2, and H.-C. Chang1. (1) Chemical and Biomolecular Engineering, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, IN 46556, (2) Chemical & Biomolecular Engineering, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, IN 46556

It is well known that silica particles on the order of 100 nm have an electrical conductivity < 10-7 S/m, much less than even that of deionized water, ~ 20 ÁS/m, and still exhibit positive dielectrophoresis (DEP) when suspended in such a low conductivity electrolyte. Such behavior is commonly attributed to Stern layer adsorption of surface charges. This increased surface charge density on the particle surface facilitates ion and electron transport around the particle and can thus give rise to an increase in the effective conductivity of the particle enabling low conductive particles to still exhibit positive DEP in a media of greater conductivity.

The frequency at which the induced particle dipole goes to zero, known as the crossover frequency, is highly dependent on the surface conductance of the particle. We have shown previously that DNA hybridization on the surface of a 100 nm functionalized silica particle leads to detectable surface conduction changes which make it possible to detect DNA hybridization reactions by simply measuring changes in particle suspension crossover frequency (cof).

In this work we utilize the above mentioned phenomena to detect the malaria species Plasmodium falciparum in an infected red blood cell suspension. Additionally, it is shown that DEP can not only be used as a genetic sensor, but can also be utilized to optimize the conditions for which particle surface hybridization takes place. By varying the particle surface concentration of oligonucleotide it is shown that a suspension cof can determine the optimal surface concentration for which hybridization can occur. Additionally, since the cof is sensitive to the length of the DNA strand, we also demonstrate the ability to identify different species of malaria based on differences in their PCR amplified DNA lengths.