(426a) DNA Patterning on Carbon Nanotube-Based Sensors Resolved By X-Ray Scattering Interferometry

Single-walled carbon nanotubes (SWCNTs) with adsorbed nucleic acids have been applied in biomolecular sensing applications to investigate biological systems at requisite spatiotemporal scales. SWCNTs display tissue-transparent and photostable, yet sensitive, near-infrared fluorescence that render them uniquely suited for visualizing dynamic biological processes, including neurotransmitter signaling in the brain. Noncovalent adsorption of polymers such as DNA onto the SWCNT surface is implemented to disperse the otherwise hydrophobic SWCNTs in solution, while also providing a molecular recognition element that confers analyte specificity, giving rise to a nanosensor. Establishing rational design rules to inform development and refinement of such nanosensors requires an understanding of the discrete nanoscale architectures. To date, observations have been restricted to computational models or experiments completed under dehydrated states, despite expected morphological differences in solution and ultimate application within aqueous biological environments.

In this work, we demonstrate a direct mode of measuring in-solution nucleic acid geometries on SWCNTs via high-throughput X-ray scattering interferometry (XSI). This technique leverages the interference pattern produced by ordered AuNP tags conjugated to the DNA on the SWCNT surface. We employ XSI to quantify distinct surface-adsorbed morphologies for two different DNA oligomer lengths, conformational changes as a function of ionic strength, and the mechanism of dopamine sensing for a previously established DNA-SWCNT nanosensor technology, with corresponding ab initio modeling for visualization. We find that the shorter ssDNA adopts a highly ordered structure of alternatingly oriented rings stacked along the SWCNT axis, in comparison to the longer ssDNA that wraps helically. For the shorter ssDNA, the presence of the target analyte dopamine leads to simultaneous axial elongation and radial tacking of the ssDNA closer to the SWCNT surface, distinct from conformational changes elicited in the presence of high ionic strength. Application of XSI to probe solution-phase morphologies of nanoparticle-based tools will elucidate the mechanism of sensor function and guide future design strategies.