PhD Defense by Ting Wang
Ph.D. Thesis Defense Announcement
Investigation on Locally Enhanced Electric Field Treatment (LEEFT) for Bacteria Inactivation Using Lab-on-a-Chip Platforms
Dr. Xing Xie
Dr. Ching-Hua Huang, Dr. Spyros Pavlostathis, Dr. Thomas DiChristina, Dr. A. Fatih Sarioglu
Date & Time: 11/14/2022 3:00 pm
The growth of undesired bacteria causes numerous problems, so seeking for efficient antimicrobial approaches is of great significance. Locally enhanced electric field treatment (LEEFT) is an emerging antimicrobial technique that uses electrodes decorated with sharp objects, such as metallic nanowires, to create locally enhanced electric field for bacteria inactivation. This thesis aims to improve the fundamental understanding, elucidate the mechanism, expand the abilities, and optimize the performance of LEEFT using operando investigation approaches. LEEFT is designed to inactivate bacteria by electroporation. A lab-on-a-chip device with curved platinum electrodes is developed for rapid determination of the electroporation threshold for bacteria inactivation. The LETs of Staphylococcus epidermidis range from 10 kV/cm to 35 kV/cm under different pulsed electric field conditions, decreasing with the increase of pulse width, effective treatment time, and pulsed electric field frequency. To elucidate the mechanism of LEEFT, the bacteria inactivation process is studied in situ on a lab-on-a-chip that has nanowedge-decorated electrodes. Rapid bacteria inactivation occurs at the nanowedge tips where the electric field is enhanced due to the lightning-rod effect. Electroporation induced by the locally enhanced electric field is the predominant mechanism. Quick membrane pore closure indicates that electroporation is induced in LEEFT, and no reactive oxygen species (ROS) is detected when >90% bacteria inactivation is achieved. LEEFT is further demonstrated to be able to induce ultrafast bacteria inactivation with nanosecond electrical pulses. A single 20 ns pulse at 55 kV/cm has achieved 26.6% bacteria inactivation, with ten pulses at 40 kV/cm resulting in 95.1% inactivation. LEEFT lowers the applied electric field by about 8 times or shortens the treatment time by at least 106 times, compared with the system without nanowedges. According to simulation, when the membrane of the cell located at the nanowedge tip is directly charged by the concentrated charges at the tip, it is much faster and to a much higher level, leading to instant electroporation and cell inactivation. To optimize the performance of LEEFT, the antimicrobial efficiency and oxidative stress under a variety of treatment conditions are tested. Higher electric field and longer pulse width could achieve higher antimicrobial efficiency. Oxidation is more likely to be induced by higher duty cycle, which may generate bubbles and by-products. The trade-off between the high antimicrobial efficiency and low oxidation generation is achieved by applying 2 μs pulses at 7 ~ 8 kV/cm and 500 Hz (duty cycle 0.1%), which results in 80% ~ 100% bacteria inactivation. Medium with higher conductivity could improve the bacteria inactivation efficiency. The ranking of LEEFT performance on different microbes is spherical Gram-positive bacteria > rod-shaped Gram-positive bacteria> rod-shaped Gram-negative bacteria > algal cells. The findings shown in this thesis improve the fundamental understanding and promote the further applications of LEEFT.