Microfluidic Device for the Electrokinetic Manipulation of Single Molecules

Manipulation and trapping of single molecules in solution is a useful tool for studies of biological molecules and molecular dynamics, but has to date been implemented in only one or two dimensions. The goal of the research in this thesis is to develop a microfluidic device to address the need for three-dimensional manipulation of single fluorescent molecules in solution. The device consists of two pairs of platinum electrodes deposited onto two standard borosilicate glass coverslips via ultraviolet microlithography and ionic sputtering. The two coverslips are sandwiched together such that the electrode tips form a tetrahedral configuration, and by applying appropriate, digitally controlled voltages to each of the four electrodes, the apparatus generates an electric field of selectable directionality and magnitude in the region centered among the electrodes. This field is used to induce motion of the molecule that is to be manipulated through both electrophoresis, for the case of a charged target, and electro-osmosis, for an ionic solution. With the implementation of a Köhler epi-illumination scheme, wide-field imaging with an electron-multiplying charge-coupled device (EM-CCD) is used to visualize the motion of latex beads, which range in size from 624 nm to 1.091 μm, and to thereby characterize the electrophoretic and electro-osmotic motion.