Nonlinear electrokinetics of the bacterial cell envelope for applications in biomicrofluidics

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 211-227).
Mathematical modeling is a powerful tool to improve the fundamental understanding in life sciences and to guide experiments. In this thesis, we primarily focus on developing a modeling platform for the electrokinetic ion transport around bacterial cell envelope under the influence of externally applied electric fields. The ability to understand the physics of this ion transport has experimental applications in cell envelope phenotyping of bacteria, cell sorting, intracellular delivery of nucleic acids for genetic engineering, and cell-cycle arrest for controlling antibiotic resistant bacteria. In the first part of my thesis we model the direct current (DC) electric field polarizability of two strains of Streptococcus Salivarius bacteria - fibrillated and unfibrillated, which differ in their cell envelope appendage (soft layer) properties. Using the Poisson-Nernst-Planck equations for ion transport and Stokes equation for fluid flow, we model the electric double layer polarization within and outside the soft layers to calculate the polarizability for these two strains. Firstly, we demonstrate that soft layers have significant influence on the polarizability of bacteria, especially when the soft layer conductivity is much higher than the buffer conductivity (high soft layer Dukhin number). Secondly, we demonstrate a significant difference in the polarizability of these two strains in the high soft layer Dukhin number regime, highlighting the potential use of polarizability based separation (using dielectrophoresis) of two very similar strains of bacteria. We have extended our model to alternating current (AC) fields and demonstrated a transition from cell envelope dominated polarizability at low frequencies (-kHz) to intracellular polarizability at high frequencies (-MHz). The model agrees qualitatively with the experimental literature on AC field polarizability. In the second part of my thesis, we perform finite-element simulations to model the influence of soft laye
by Naga Neehar Dingari.
Ph. D.