Interaction of Fluorescent Single-Walled Carbon Nanotubes with Photosynthetic Microbes

The discovery of carbon-based nanomaterials has impacted a variety of research areas in ways that could not be imagined three decades ago. Their unique combination of structural, optical, and electronic properties has made these nano-sized materials particularly attractive for applications in biotechnology and biomedicine, ranging from sensing, bioimaging, and therapeutics. When appropriately functionalized, nanocarbons (NCs) can overcome the cellular barriers of living organisms, and localize within specific organelles, providing alternative tools for the characterization and manipulation of important processes at a cellular level.

In particular, the fluorescence properties of semiconducting single-walled carbon nanotubes (SWCNTs) provide a practical basis for not only studying cellular dynamics, but also investigating the mechanisms of nanoparticle transport inside cells of living organisms. The internalization of SWCNTs in living cells forms the basis for new technologies in cellular imaging, gene and drug delivery, and other biological and medical whole-cell applications. New areas of research have focused on the targeted integration of engineered SWCNTs into living photosynthetic organisms. The synergistic combination of SWCNTs with plants and algae has the potential to impart photosynthetic organisms with improved capabilities, such as accelerated growth and enhanced photosynthetic activity, expanding their use for novel agricultural or electronic applications.

Although most work has thus far focused on studying the impact of SWCNTs on plants and other eukaryotic organisms, the impact of SWCNTs on prokaryotic species has remained largely unexplored. A study currently lacking in the field is elucidating the physiochemical factors that affect SWCNT transport across the cell wall architecture of prokaryotes, which is crucial for unlocking the variety of applications enabled by SWCNTs.

This thesis will examine the key elements, such as size and surface chemistry, that govern the interaction of fluorescent SWCNTs with photosynthetic microbes. In particular, the work presented herein will explore SWCNT uptake in both unicellular and filamentous strains of cyanobacteria, a well-known model organism for the study of photosynthesis and for use in industrial and biotechonological applications. We demonstrate length-dependent and selective internalization of SWCNTs decorated with small positively charged proteins and discuss SWCNT uptake mechanisms. Furthermore we examine subcellular localization of nanoparticles and the species-dependent impact of SWCNT exposure on cell viability.

The localization of SWCNTs within the internal cell compartments shown in this study, combined with the sustained viability of the cells, opens multiple opportunities for future developments of "green" technologies based on SWCNT integration into photosynthetic microbes. Exemplary applications, highlighting the scope of these technologies, are presented in the final chapter of this thesis. These include investigations on the impact of functionalized-SWCNT incorporation into bio-hybrid devices for improving bio-electricity generation from cyanobacteria, as well as preliminary findings on the suitability of these materials as scaffolds for targeted biomolecule delivery.