DIELECTROPHORETIC MANIPULATION AND SEPARATION OF MICRO- AND NANOSCALE PARTICLES: EXPERIMENTAL AND COMPUTATIONAL STUDIES

Abstract

Dielectrophoresis (DEP) is a powerful, label-free technique for manipulating micro- and nanoscale particles in non-uniform electric fields based on their dielectric properties. This thesis presents a comprehensive study integrating theoretical modeling, microfluidic device fabrication, COMSOL simulations, and experimental investigations to characterize and optimize the DEP-based separation and manipulation of biological particles, with a particular focus on coronaviruses. Theoretical analysis is first conducted to define key parameters such as crossover frequency, electrical conductivity, polarization, and relaxation time, all of which influence DEP behavior. Microparticles with diameters of 1.03, 2.37, 4.42, and 6.83 μm are experimentally analyzed to determine their crossover frequencies under varying electric field conditions and medium conductivities. The impact of electrode trap geometry and particle release orientation (horizontal vs. vertical) on trapping efficiency is also explored through both experimental and numerical approaches. The study then advances to the separation and characterization of three coronaviruses, SARS-CoV-2, Human Coronavirus 229E, and Betacoronavirus 1, using a custom-fabricated microfluidic DEP platform. Virus particles were labeled with SYBR Green and AB to examine the effect of staining methods on crossover frequencies and DEP behavior. Results demonstrate distinct DEP responses for each virus, influenced by particle size, labeling technique, and frequency range, with successful trapping observed across a broad voltage and frequency spectrum. COMSOL Multiphysics simulations complement the experimental findings by modeling electric field distributions and force profiles around nanoscale particles. Staggered electrode trap designs are evaluated to enhance separation efficiency. This integrated framework of theory, experimentation, and simulation offers valuable insights for the development of rapid, scalable, and label-sensitive viral detection platforms, with implications for future diagnostics and pandemic response strategies. The study at last investigated microparticles trapping efficiency in a microfluidic device by examining the combined influence of particle release height, electrode trap gap, and particle diameter using a COMSOL Multiphysics finite element model. The simulation integrated electrostatics, creeping flow, and particle tracing modules to capture the interaction between hydrodynamic drag and DEP forces under laminar flow conditions. Four particle diameters (1.02, 2.37, 4.42, and 6.83 μm) were evaluated across multiple release heights and trap gap configurations. Results showed that trapping efficiency strongly depends on particle size and geometric parameters, with smaller particles exhibiting highly sensitive behavior to release position and trap dimensions, while larger particles demonstrated more robust trapping over a wider operating range due to stronger DEP force scaling with particle volume. Among all tested configurations, a trap gap of approximately 40 μm consistently provided the highest and most stable trapping efficiency, whereas intermediate release heights of 12–15 μm yielded optimal particle capture.