Redox-magnetohydrodynamic (MHD) microfluidics: Fundamentals, optimization, and applications to analytical chemistry.

摘要

Microfluidic systems are of great interest in analytical chemistry for the development of lab-on-a-chip devices. This dissertation describes fundamental investigations of magnetohydrodynamics with added redox species (redox-MHD) as a new microfluidic approach for use in analytical applications. Redox-MHD is attractive because it offers a unique combination of desirable features that are otherwise only available separately with individual micropumps. Redox-MHD is compatible with aqueous and nonaqueous solutions, does not require moving parts, easily reverses flow direction, and requires only low voltages. An ion flux is generated from the oxidation or reduction of an electroactive species at specific locations by activated electrodes patterned on the chip. In the presence of a magnetic field perpendicular to the ion flux, a magnetic force is generated to induce solution convection. This convection is visualized using microbeads to track fluid flow over microband electrode arrays to investigate redox-MHD in a confined solution. The effects of concentration of redox species, widths of electrodes, gaps between electrodes, and applied potentials and currents on flow velocities are discussed. A significant result is the fairly flat flow profile attained in the gap between electrodes that are oppositely biased. A novel method for maximizing flow velocities in order to lower the necessary concentration of redox species to perform pumping is presented. Velocities were increased by as much as 70% from control experiments using the technique. Redox MHD-induced convection was also shown to be compatible with and used to transport components of an immunoassay (without channel walls) while simultaneously detecting an enzymatically-generated electroactive species. Key findings include much lower concentrations of redox-pumping species than were originally anticipated, enzymatic activity was sustainable in the presence of those pumping species, detection signal easily separated from pumping signal, and direction of fluid motion controlled by active electrode placement instead of reconfiguring channel walls or controlling valves. These results suggest that a general design of a microfluidic device could be utilized for a broad range of flow patterns and applications.