(652e) Dielectrophoretic Detection of of Hybridized Genetic Bead Suspensions Using a Novel Suspension Kaleidoscope Approach

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 µS/m, still exhibit positive dielectrophoresis (DEP) when suspended in such a low conductive electrolyte. Such behavior is commonly attributed to Stern layer adsorption of surface charges. This increased surface charge density on the particle surface facilitates 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. In this work we consider the effect that DNA hybridization has on the surface conductance of a silica particle of varying diameters ranging from 100 nm ? 1 ìm and exploit such detectable changes in order to rapidly detect DNA hybridization reactions. Instead of detecting particle crossover frequency through the tracking of individual particles, we take a novel DEP suspension pattern approach.

By designing a quadrupole micro-electrode with specific symmetries and length scales comparable to the average suspension screening length, we are able to overlap the different suspension aggregates into a kaleidoscope of two dimensional suspension patterns with different symmetries and anti-symmetries (See Fig. A-B). An open orifice exists at the center of the quadrupole for positive DEP and a closed circular aggregate appears for negative DEP. Unlike previous DEP colloidal results, the reported suspension pattern orifice dimensions are highly dependent on the field frequency and particle surface charge, and unlike traditional crossover frequency measurements, can be used to directly calculate the field induced DEP particle force.

Additionally, the detection of particle surface conductance typically requires the determination of multiple crossover frequencies of either particles suspended in various electrolyte conductivities, or of particles of varying sizes. It will be shown that the novel suspension pattern method allows accurate determination of surface conductance through the analysis of only one suspension pattern consisting of silica particles of varying size. Therefore, this novel suspension pattern approach allows one to determine the DEP force, the particle crossover frequency, and the particle surface conductance, and hence whether or not a particle surface has undergone DNA hybridization, from only one sample and in only a few seconds.