A microfabricated dielectrophoretic trapping array for cell-based biological assays

Abstract

This thesis presents the development of a small planar array of microfabricated traps for holding single cells and performing assays on them. The traps use the phenomenon of dielectrophoresis-the force on polarizable bodies in a non-uniform electric field-to make potential energy wells. These potential energy wells are electrically switchable, arrayable, and amenable to batch fabrication. The trapping arrays have potential use as a cytometer for monitoring the dynamics of populations of single cells and then sorting those cells based upon those dynamics. To design such traps, I have developed a modeling environment that can absolutely predict the ability of DEP-based traps to hold particles against liquid flows, which are the dominant destabilizing force in these systems. I have used the common easy-to-fabricate planar quadrupole trap to verify the accuracy of these modeling tools, and in the process determined why planar quadrupole traps behave as they do. I next used the modeling tools to design an improved quadrupole trap-the extruded quadrupole-that has the potential to hold particles lOx-100x stronger. The extruded quadrupole trap consists of a set of microfabricated gold posts arranged in a trapezoidal fashion, to ease trap loading, and includes metal substrate shunts to improve performance. The fabrication process for small arrays of these traps uses electroplating of gold into an SU-8 mold to achieve the required geometries. The final section of the thesis details experiments using small arrays of these extruded quadrupole traps. Experiments were performed with beads to verify the strong nature of the trap and then with cells to demonstrate qualitative operation of the arrays and the ability to perform dynamic fluorescent assays on multiple single cells followed by sorting. The technology is now well poised to enable the development of biological assays that are currently unavailable.