Loading...

The Synthesis of Graphene-Nanobubbles and Investigation of their Potential Synergistic Effect on Bacterial Cells

Jannesari, Marziyeh | 2019

453 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52639 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Akhavan, Omid; Maddah Hosseini, Hamid Reza; Bakhsi, Bita
  7. Abstract:
  8. Recently, nanotechnology has promised to create and/ or improve therapeutic methods which in turn remain minimum side effects by employing synergistic effects of nanostructures. However, a comprehensive understanding of the interactions between nanostructures and building blocks of the biological systems (cells) is essential to create innovative therapeutic methods and compound and also predict their behavior for upcoming applications. In this thesis for the first time, synergistic effects of graphene-nanobubbles in interactions with bacterial (as the simplest model) cells were investigated. Therefore, at the first step, production of nanobubbles (NBs) in the presence of two-dimensional graphene structures was investigated. Thereafter, their potential application in growth inhibition of bacterial cells were considered. In this study, two different (including physical and in-situ chemical) strategies were introduced to produce NBs. In the first strategy, spontaneous physical generation of NBs was developed by using a superfast microvortex platform in the presence of graphene oxide (GO) sheets. Very high energy dissipation rate through discharging warm water into N2 pre-saturated cold water resulted in creation of microvorteces and sheer stresses. These phenomena followed by pressure fluctuations and consequently, gas local supersaturation in the liquid (in the scale of microvortecs) leaded to NBs formation. Adjusting the energy dissipation rate of the system (by changing the discharge speed and/or temperature differences of warm and cold water) effectively controlled the length of microvortices and therefore both the size and concentration of NBs. On the other hand, introducing GO sheets into the system, by providing energetically favorable sites for prompt heterogenous nucleation as well as accelerating energy dissipation rate of the system further controlled over the NBs formation. Interestingly, decreasing the lateral size of GO sheets from 800 to 150 nm significantly reduced the size of NBs from ~180 to 40 nm. The second strategy, however, introduces a series of nanocomposite systems, capable for chemically producing in-situ oxygen NBs. These nanocomposites consist of reduced graphene oxide/ metal peroxide (such as copper peroxide (rGO/CuO2) or zinc peroxide (rGO/ZnO2-Ag)) as the solid source of oxygen releasing oxygen NBs in response to the environment, meaning pH and temperature. A dynamic micro/nano-environment has been proposed due to evolving, growing and collapsing or shrinking O2 nanobubbles (NBs) around the nanocomposites after exposing to the phosphate buffer saline. Beside a controlled oxygen delivery, evolved O2 NBs in the presence of rGO provided superior antibacterial properties, correlated to the respiratory pathway interruption. Indeed, rGO as an external electron acceptor can harvest a portion of respiratory electrons and transfer them to the O2 NBs, resulting in reactive oxygen species (ROS) generation. This effect along with the disturbance in prerequisite energy supply leaded to a significant bacterial growth inhibition on both Gram-positive Staphylococcus aureus, Gram-negative Escherichia coli and more importantly, methicillin-resistance Staphylococcus aureus bacteria. Neither rGO nor O2 NBs, induced considerable ROS production, when co-cultured with the bacteria (which resulted in slighter interactions) supporting the hypothesis. Furthermore, near-infrared laser irradiation caused much more loss of cell membrane integrity due to the local heat elevation as well as promoted oxidative stress levels
  9. Keywords:
  10. Synergistic Effect ; Graphene Structures ; Nanobubbles ; Cellular Interaction ; Bacterial Cells

 Digital Object List

 Bookmark

No TOC