CATALYTICALLY PRODUCED ELECTROKINETICS: TOWARDS CHANNELESS MICROFLUIDICS

Open Access
Author:
Zhang, Jiayun
Graduate Program:
Agricultural and Biological Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 16, 2009
Committee Members:
  • Jeffrey M Catchmark, Thesis Advisor
Keywords:
  • Catalysis
  • Electroosmosis
  • Electrophoresis
  • Microfluidics
Abstract:
Microfluidics has been demonstrated as a cornerstone technology in environmental testing and biological, chemical, biomedical, clinical and forensic analysis. This technique yields advantages of high-throughput analysis and low consumption of reagents. Microfluidic devices are now entering the market and focusing on flexibility and usefulness in various applications, but spatial control over biological molecules and micro-/nano-size structures in fluid environment with simple instruments is still a problem. External optical fields, magnetic fields, and electric fields have been explored to be compatible with microfluidic devices to provide sufficient forces in order to control motion of micro-/nano-size molecules and structures. However, the complex fabrication process and associated instrumentation still limit their practical applications. In this thesis, chemically powered channelless microfluidic devices were designed, fabricated, and characterized. Bimetallic devices consisting of silver and gold catalytic junctions can generate a proton gradient and an associated electric field which in turn drives electroosmosis, and electrophoresis when a charged particle is present in the vicinity of the field during the reaction of hydrogen peroxide decomposition. The influences of patterned regions of different surface zeta potential, device geometry and size on the motility of negatively charged carboxyl-functionalized microspheres were evaluated. Carboxyl-functionalized microspheres were chosen in part to simulate negatively charged biomolecules. Rectangular silver features patterned on a gold thin film with different surface zeta potentials were used to evaluate the impacts of bimetallic feature geometry on the motility of carboxylated spheres. The width of silver features was held constant at 50 µm and the lengths were 200 µm and 300 µm. Amine terminated self-assembled monolayer (SAM) was used to modify the surface zeta potential, which in turn controlled the direction and magnitude of electroomostic fluid flow. This manifested itself as a depletion region around both the silver feature and the area where the SAM had been assembled. On the gold surface without SAM modification, the depletion region extended to ~ 15-20 µm away from the edge of silver features, while on the gold surface with SAM modification, it extended to ~ 85 µm as electroosmotic fluid flow was aligned with electrophoretic force for negatively charged particles. Velocities of microspheres increased in the case where a larger silver catalyst area was implemented. In addition, velocities of microspheres decreased gradually as distance to silver edge became larger. In addition, some practical channelless microfluidic devices were designed and demonstrated. In particular, a device exhibiting a circular silver-gold bimetallic catalytic junction fabricated on a silicon dioxide surface is capable of focusing particles into a defined region on the surface, where their density was ultimately increased by a factor of 10. Velocity of tracers in the region of 0-50 µm away from the silver edge was 45 ± 5 µm/min, which was twice as large as that at the region of 50-100 µm. Little variation in velocities were observed when the dimension was larger than 50 µm. This device and other similar devices may open the possibility of integrated chemically powered channelless microfluidic devices. The efficiency and ease of the fabrication suggest the possibility of versatile applications.