Ph.D Thesis

Ph.D StudentGolan Saar
SubjectDifferentiation of Multi Species Biofluids by
Dielectrophoretic Field Flow Fractionation
DepartmentDepartment of Biomedical Engineering
Supervisors PROFESSOR EMERITUS Uri Dinnar (Deceased)
PROF. David Elata


The separation of distinct particle populations (species) present within a fluid is fundamental in numerous scientific and medical areas (e.g., blood analysis). Currently, this process (fractionation) is often implemented using labeling techniques. However, labeling is expensive due to the costly fluorescent moieties and fluorescence activated cell sorter (FACS) machines and may impede further use of the tagged species or alter its properties.

Microfluidics offers many advantages to diagnostic apparatus (e.g., reduced reagent quantities). Microfluidic studies often deal with flows inside miniaturized devices (‘Lab-on-a-chip’) that contain microchannels. These channels, traditionally fabricated using time-consuming and costly microelectronics processes, constitute a major challenge in the development of affordable (disposable) medical devices.

Recently, financial and commercialization considerations have motivated the development of fabrication techniques such as soft lithography. In soft lithography, a master (mold) is fabricated using traditional microelectronics techniques and then employed in the mass production of polymer-based (e.g., polydimethylsiloxane) replicas - copies. This process significantly reduces the replica price and expedites fabrication. However, the master’s costly and time-consuming fabrication does not warrant economically viable devices unless vast amounts of replicas are produced.

Microfluidics has motivated novel fractionation methods such as dielectrophoresis that are more compatible with Lab-on-a-chip devices. Dielectrophoresis presents distinct advantages (e.g., the separated particles are not physiologically altered) and is receiving increasing attention.

Recent advances in microfluidics and separation technologies have enabled highly effective Lab-on-a-chip prototypes to be fabricated and employed. Nevertheless, few of these prototypes have matured beyond academic research to reach commercial products since they are still too costly and their fabrication schedule too time-consuming.

The study motivation is to advance Lab-on-a-chip devices, with strong emphasis on technologies that facilitate economically viable products. To this end, generic research was conducted in several areas and the contributions made are presented: (1) A fabrication technique for polydimethylsiloxane microchannels that does not require a master, is rapid, economical and inherently suitable for fabricating disposable devices. (2) A characterization technique for thin compliant layers that is based on the well-established bulge test but employs plate rather than membrane mechanics. This technique uses widespread laboratory equipment, is straightforward and economical and presents an appealing alternative to less accessible techniques such as biaxial testing. (3) A technique implementing dielectrophoresis that employs electrically floating electrodes to overcome the prerequisite to apply voltage to all field generating electrodes. This technique can facilitate device miniaturization by removing bulky interconnects and is ideal for manipulating nanoparticles using floating nanoelectrodes.