With waves of life-threatening infectious disease outbreaks in the past decades ? including the surges of drug-resistant superbugs ? the importance of developing new or alternative antimicrobial agents is unarguably clear. Although metal nanoparticles, such as silver nanoparticles (AgNPs), have attracted broad interest and attention for their capability of killing bacteria and other microbes, the exact mechanisms of their antimicrobial activities have remained unclear. In this project, the research team developed and utilized advanced imaging tools (including super-resolution fluorescence microscopy and single-particle tracking), coupling with biochemical assays, to understand the fundamental antimicrobial mechanisms of AgNPs. The study has so far resulted in more than 15 journal articles, several book chapters, and one patent. Using quantitative super-resolution fluorescence microscopy, it was observed that the spatial organization of H-NS protein (a DNA-associated regulatory protein in E. coli bacteria) was significantly changed in the bacteria when subjected to AgNPs. Such spatial reorganization of the proteins was dependent on the charge and surface modifications of the AgNPs. These dependencies were further quantified by AgNPs coated with polydopamine of different thickness, from which synergistic antimicrobial activities were observed. Additionally, a new method was also developed for high-throughput evaluation of the growth of bacteria based on multimode microplate readers.The dynamic diffusion of individual H-NS proteins in live bacteria were also investigated. It was measured that silver caused weaker binding between H-NS protein and DNA, leading to faster diffusion of H-NS proteins inside bacteria. Meanwhile, a new method based on bent DNA molecules was developed and used for studying DNA interactions with other molecules, resulting in a granted patent. Furthermore, we quantified how the diffusion of H-NS protein depends on the temperature and developed a new theory to examine the validity of the well-known Einstein relation in live bacteria and cells, which has been challenged in the past decade. Our results showed that the Einstein relation could remain valid in living systems, and fundamentally changed how bacterial cytoplasm should be viewed. The effects of AgNPs on bacterial membrane and morphology were also quantified, suggesting that AgNPs illuminated by a blue laser were significantly heated up due to their surface plasmon resonance and thus damaging the membrane. During the silver treatment, the bacteria grew and shrank back and forth. Such oscillatory behaviors indicate that  the bacteria attempt to adapt to a silver-containing environment. The bacteria?s adaptability to silver  suggests that care must be taken with regards to using AgNPs as antimicrobial agents, a concern that was rarely raised in the literature. 

In addition to the publications, the results from this project were further disseminated through presentations at the professional conferences to the relevant scientific communities. The new knowledge generated from this award is expected to provide better guiding principles on the design, production, and usage of metal nanoparticles for antimicrobial applications in various fields ? such as food safety, sanitization and disinfection in residential and industrial settings, and hospital infection-treatments, which in the long term is expected to improve U.S. public health and benefit the whole society. Comprehensive education and outreach activities have also been implemented. During the funding period of this project, 10 graduate students and 12 undergraduate students have been involved in this research. These students were trained in the emerging field of nanomaterials synthesis and characterization, and super-resolution fluorescence microscopy. Furthermore, the Nanoscopy for Nano-Bio Advanced Science Modules (NNBASMs) were developed and integrated into courses at both graduate and undergraduate levels, as well as annual workshops at the  state-wide conferences. These activities of integrating research and education have increased student participation in STEM research and trained the next-generation work force in the interdisciplinary field of nano-bio interactions, which is expected to reinforce and improve the United States' future competitive strengths in STEM fields.

Last Modified: 02/14/2023
Modified by: Yong Wang