TEM Studies of Multielement Nanomaterials and Bacteria Interactions in the Aqueous Environments

The understanding of nano-bio interactions between bacteria and nanomaterials has gained substantial interest in the biomedical field. Among the various available means for studying behavior of bacteria in the presence of nanomaterials, transmission electron microscopy (TEM) has emerged as a promising technique due to combined imaging and spectroscopic capabilities at sub-nanometer scale. In-situ graphene liquid cell (GLC) scanning transmission electron microscopy (STEM) approach was utilized to evaluate the interaction of multielement FeNiCu ternary metal nanoparticles with Escherichia Coli (E.Coli) bacteria. GLC systems can acquire atomic resolution imaging with higher signal to noise ratio and can mitigate the charging effects avoiding the electron beam induced radiolysis damage of biological soft matter. STEM-energy dispersive X-ray spectroscopy (EDS) elemental analysis of S, P, O, C, N, and Cl diagnostic ions in bacterial cells confirmed the cell membrane damage and cytoplasmic leakage. The metal ions release antibacterial mechanism of action of multielement FeNiCu ternary metal nanoparticles was evaluated using STEM-EDS. Results show that the release of Cu ions was much higher than those for Ni while the Fe release was the lowest. The binding affinity of bacterial cell membrane protein functional groups with Fe, Ni, and Cu cations is found to be the driving force behind the selective metal cations release from the multi-principal element nanoparticles following. To achieve enhanced bacterial growth, a novel category of multielement nanoparticles – polyelemental glycerolate particles (PGPs) were interacted with E.Coli bacteria. The PGPs were synthesized by achieving coordination between multiple metal cations with the glycerol (Gly) matrix using solvothermal route. Results indicate 2.75 fold, 3.5 fold, and 7.28 fold exponential growth of E.Coli bacteria upon 4 hours of interaction with unary Gly-Ni, binary Gly-NiZn, and quinary Gly-NiZnMnMgSr particles, respectively, in comparison with control E.Coli bacteria. The triggered biofilm formation upon controlled release of multiple metal cations from PGPs was evaluated as a primary reason for the exponential increase in bacterial growth. High entropy nanomaterials have gained tremendous attention owing to their superior structural, physicochemical, and tunable elemental compositional properties. The thesis work also focuses on the synthesis of novel category of (Mn, Fe, Ni, Cu, Zn)3O4 high entropy oxide (HEO) nanoparticles. The cost-effective and ultrafast flame spray pyrolysis route was utilized. The spinel phase metal oxide (Mn, Fe, Ni, Cu, Zn)3O4 of traditionally immiscible five elements, ultrafast heating and cooling rates during synthesis were the strategic aspects of the study. Additionally, the electronic state stability and the variation of chemical oxidation states of individual transition metal cations were utilized using STEM-electron energy loss spectroscopy (EELS) technique. The study includes the systematic chemical oxidation states analysis of L3 (2p3/2) and L2 (2p1/2) white lines of binary (Fe, Mn)3O4, ternary (Mn, Fe, Ni)3O4, and quinary (Mn, Fe, Ni, Cu, Zn)3O4 polyelemental transition metal oxide nanoparticles. The nanoscale investigation of HEO nanoparticles would provide important fundamental understandings for designing multielement nanoparticles, potentially paving the way towards design rules for biomedical field application-driven studies.