Real-time pathways of hierarchical self-assembly in artificial light-harvesting nanotubes
Nature has perfected the art of self-assembly, in which disordered individual components spontaneously organize to form ordered structures. A prime example is the light-harvesting antennae (chlorosomes) in green sulfur bacteria, which absorb sunlight and efficiently transport energy for photosynthesis. In his thesis, Sundar Krishnaswamy investigates how individual dye molecules (labeled C8S3) spontaneously organize into double-walled cylindrical nanostructures upon the addition of water, structures reminiscent of chlorosomes in green sulfur bacteria.
Krishnaswamy begins by investigating how outer nanotube reforms after selective dissolution, and extends these insights to the complete self-assembly process. He concludes by exploring how guest molecules influence self-assembly dynamics and the resulting double-walled structure.
Krishnaswamy employs a microfluidic system in which reagents are mixed, establishing precise timing: the mixer marks "time zero," and as the sample flows downstream, self-assembly proceeds spatially. By sampling at different flow-cell positions, Krishnaswamy captures snapshots of assembly at known time intervals, enabling real-time observation. He combines optical spectroscopy and electron/optical microscopy to reveal the whole picture. The former infers the underlying molecular structure by studying how molecules absorb and emit light, while the latter visualizes physical features such as diameter and length. Together, these methods reveal both the molecular-level details and the macroscopic organization during self-assembly.
The results establish a general framework for real-time monitoring of self-assembly. This understanding of how molecules cooperatively build complex architectures from the bottom up provides fundamental insights into self-organizing systems. Such knowledge has broad implications for nanotechnology, materials science, and our understanding of how nature constructs sophisticated molecular systems.