Antibacterial activity of carbon nanomaterials.
Date of Issue2012
School of Chemical and Biomedical Engineering
Carbon nanomaterials (CNMs), including graphene based materials, carbon nanotubes and fullerene, have been intensively studied in recent years because of their unique properties and various potential applications. This thesis focuses on the antibacterial activity of CNMs, more specifically, one-dimensional single walled carbon nanotubes (SWCNTs) and two dimensional graphene based materials, including graphite (Gt), graphite oxide (GtO), graphene oxide (GO), and reduced graphene oxide (rGO). First, the antibacterial activity of high purity SWCNTs was investigated. The results demonstrate that individually dispersed SWCNTs exhibited much higher antibacterial activity than SWCNT aggregates toward several types of bacteria. Ultraviolet–visible spectroscopy absorption spectroscopy study at 260 nm and scanning electron microscope images reveal that the bacterial death is related to the destruction of bacterial membrane. Next, antibacterial mechanism of SWCNTs was explored. My results suggest that inhibition of cell and oxidative stress induced by superoxide anion (O2•−) are not the major causes Furthermore, the effects of Cobalt on SWCNT samples can be ruled out. The physical interactions between SWCNTs and bacteria were investigated by atomic force microscopy. Results demonstrate that individually dispersed SWCNTs in solution develop nanotube networks on bacterial surface, which destory the bacterial envelopes with leakage of intracellular contents. Further analysis indicates that a single collision between one nanotube and bacterial cell is unlikely to introduce direct physical damage. Hence, antibacterial activity of SWCNTs is the accumulation effect of large amount of nanotubes through interactions between SWCNT networks and bacterial cells. Then, the antibacterial activity and mechanism of graphene based nanomaterials were investigated. GO dispersion shows the highest antibacterial activity, sequentially followed by rGO, Gt, and GtO. Scanning electron microscope images display that graphene nanosheets disrupt cell membrane. No superoxide anion (O2•−) induced reactive oxygen species production is detected. However, the four types of materials can oxidize glutathione, which serves as a redox state mediator in bacteria. Effects of lateral dimension of GO nanosheets on their antibacterial activity were also investigated. GO samples with larger lateral dimensions show stronger antibacterial activity than smaller ones. The different antibacterial activity observed among GO sheets with different lateral dimensions can be attributed to their different wrapping efficiency. Once cells are wrapped, they were biologically isolated from growth medium. Thus, cells can neither consume the nutrients nor proliferate. My results suggested that antibacterial actions of graphene based nanomaterials are contributed by membrane stress, oxidation stress and lack of nutrients. A three-step antimicrobial mechanism is applicable to graphene-based materials. It includes initial cell deposition on graphene based nanomaterials, membrane stress caused by direct contact with sharp nanosheets, and the followed superoxide anion-independent oxidation. This study elucidated antibacterial mechanism of CNMs and several factors groverning their antibacterial activity , and it provided an insight in developing strategies that can maximize the CNM antibacterial application potentials.