Operando Investigation on Locally Enhanced Electric Field Treatment (LEEFT) for Bacteria Inactivation Using Lab-On-a-Chip Devices
Author(s)
Wang, Ting
Advisor(s)
Editor(s)
Collections
Supplementary to:
Permanent Link
Abstract
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 at the single-cell level 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 confirms that electroporation is induced in LEEFT, and no generation of 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 mechanism is tuned between electroporation and electrochemical oxidation. There is a higher chance of oxidation generation with higher duty cycle, higher electric field, and longer pulse width. Although the antimicrobial efficiency is higher under these conditions, the electrochemical oxidation may generate by-products. Pure electroporation could be achieved at high electric field with short pulses and moderate duty cycle. When 2 μs pulses are applied at 7 ~ 8 kV/cm with a duty cycle of 0.1%, good antimicrobial efficiency (>80%) is achieved by pure electroporation. Medium with higher conductivity could enhance the bacteria inactivation efficiency, but also makes it easier for electrochemical oxidation. Short pulses, such as nanosecond pulses, could be used to minimize oxidation and achieve good antimicrobial efficiency. For different microbes, larger algal cells are harder to be inactivated than bacterial cells. The findings shown in this thesis improve the fundamental understanding and enhance the further applications of LEEFT.
Sponsor
Date
2022-12-08
Extent
Resource Type
Text
Resource Subtype
Dissertation