(113a) Mapping the Morphology of DNA Adsorbed on Carbon Nanotubes Using X-Ray Scattering Interferometry

Adsorption of polymers on single-walled carbon nanotubes (SWCNTs) has enabled developments in biomolecular sensing,¹in vivo imaging,² and gene delivery³ applications. As the basis for these technologies, SWCNTs display tissue-transparent and photostable near-infrared fluorescence that render them uniquely suited for visualizing biological processes. Noncovalent polymer adsorption onto the SWCNT surface is implemented to solubilize and disperse the otherwise hydrophobic SWCNT, while preserving the underlying graphitic SWCNT structure (and thus fluorescence properties). SWCNTs have been functionalized with various polymers that serve as the recognition elements for sensors, such as different sequences of nucleic acids to create optical nanosensors for small-molecule targets including dopamine⁴ and nitric oxide.⁵ However, the interfacial interactions and morphology remain difficult to study in the solution-phase in which these polymer-SWCNT constructs are ultimately applied, thus limiting rational design of future nanoparticle-based technologies.

In this work, we apply X-ray scattering interferometry with gold-tagged DNA to map out the surface-adsorbed polymer conformation on the SWCNT. This approach extends on our prior study employing X-ray scattering to understand proteins interacting with DNA-SWCNTs.⁶ The present technique enables structural studies in the solution phase and with concentrations at which the DNA-SWCNT complexes are biologically applied (~1-5 mg/L). We reveal the periodicity of helical vs. ring-like DNA structures along the SWCNTs, with inter-strand separation distances measured as a function of DNA sequence and surrounding solution conditions. Visualization with electron microscopy broadly recapitulates the in-solution scattering data. This insight into the dynamic spatial and topographical characteristics of the DNA-SWCNT complexes will help elucidate the mechanism of function and guide rational design for future nanosensors.

References

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