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Controlling Gel Electrophoresis of Nanoparticles and Molecules

Abstract

Gel electrophoresis (gelEP) provides a means of analyzing and separating charged species having characteristic sizes that span more than three orders of magnitude, from solvated atomic and molecular ions to colloidal suspensions. We present methods for controlling gelEP that go beyond its conventional use for separating nucleic acids and proteins. In contrast to traditional Cartesian gelEP geometries which have homogeneous electric fields, we develop a radially dependent electric field geometry by constructing a full-ring cylindrical electrophoresis chamber which causes particles to propagate outward from a center ring-well more rapidly at first before slowing over time in agreement with a simple model incorporating the radial electric field. Moreover, a cylindrical geometry offers the potential for improved separations per area of gel for objects having widely different sizes. Within the same area, smaller spheres can be retained for the duration of longer run times needed to separate larger objects. GelEP takes place within an electrolytic cell containing a conducting solution of ions that evolves over time. Additionally, we show that the time-dependent local electric field strength acting on mobile ions in different regions of the gel can be more accurately estimated using a constitutive conductivity model as compared to the standard model of dividing the applied voltage by the separation between electrodes. We measure conductivity near the center of the gel region, predict the electric field based on a conductivity model, and show that this prediction closely correlates with the velocity of propagating nanoparticles and molecules. Furthermore, by introducing two or more reagents with differing relative mobilities it is possible to collide the bands under the influence of an applied electric field. Image analysis of visible light photography reveals signals indicating complexation of dye molecules and other chemical reactions. Band collision electrophoresis may provide routes to kinetic studies in a similar manner to stopped-flow or molecular beam experiments. Beyond electrophoresis, we also discuss the development of a method for fused deposition 3D printing of thermoplastic geometries that can be accurately manufactured within tolerances suitable for scientific rheometry of soft materials.

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