Abstract
There is an increasing demand for the development of rapid and reliable methods for microparticle and cell separations in applications that range from clinical analysis to food and environmental safety assessments. Microfluidic systems, being portable and offering a response within minutes, are particularly attractive. Electrokinetic (EK) methods are a growing area in microfluidics, due to their robustness, rapid response time, low cost, and label-free analysis of micron-sized particles, including intact microorganisms. EK methods require the application of an electric stimulation, such as direct-current (DC) or alternating-current (AC) potentials, to induce different EK phenomena, such as electrophoresis, electroosmotic flow and/or dielectrophoresis, which are manipulated for separating analytes. DC-biased AC potentials have extra characteristics (frequency, amplitude, and magnitude of the DC bias) that can be customized to enable a desired separation process, over DC only voltages, which feature just a magnitude, and over AC only voltages, where the net migration is negligible. The present study combines modeling and experimentation to perform challenging separations such as microparticles with highly similar characteristics and separation of microorganisms by applying low-frequency DC-biased AC potentials in an insulator-based-EK (iEK) system. This research focuses on (i) evaluating how the characteristics of applied AC potentials improve the separation of highly similar microparticles, (ii) understanding the effect of the characteristics of the post arrangement in an iEK device on microparticle separations, and (iii) demonstrating the iEK-based separation of mixtures of microorganisms with increasing level of difficulty. Separation of spherical microparticles of the same size (5.1 μm), made from the same substrate material, but with a difference in particle zeta potentials of only ~14 mV, was improved by systematically studying the effect of (i) the three main characteristics for the applied DC-biased AC voltage: frequency, amplitude, and DC bias, and (ii) the insulating post arrangement: increasing the horizontal spacing and decreasing the vertical spacing between posts. Several microbial separations with an increasing order of difficulty, ranging from separating cells from different domains to cells from same domain and same species, was achieved by applying a DCbiased AC voltage, which was advantageous over applying an equivalent DC voltage. The presented study demonstrates the potential to extend the limits of iEK systems coupled with DCbiased AC voltages to carry out discriminatory separations of micron-sized entities such as microparticles and cells.
Publication Date
5-23-2024
Document Type
Dissertation
Student Type
Graduate
Degree Name
Microsystems Engineering (Ph.D.)
Department, Program, or Center
Microsystems Engineering
College
Kate Gleason College of Engineering
Advisor
Blanca H. Lapizco-Encinas
Advisor/Committee Member
Victor Hugo Perez-Gonzalez
Recommended Citation
Nasir Ahamed, Nuzhet Nihaar, "Unravelling micro-mysteries: separating microscopic entities using electrokinetic microsystems" (2024). Thesis. Rochester Institute of Technology. Accessed from
https://repository.rit.edu/theses/11793
Campus
RIT – Main Campus
