Single-stranded DNA (ssDNA) represents an excellent model system for studying the behavior of polymer-wrapped single-walled carbon nanotubes (SWCNTs). As a consequence of stabilizing individual SWCNTs through repulsive electrostatic interactions, we expect ssDNA-SWCNT dispersion properties to be influenced by background salt concentration. In this work, we study the effect of monovalent salt concentration on the optical and structural properties of ssDNA-wrapped SWCNTs and we find that a reduction in the dispersion ionic strength from 200 mM to 1 mM reversibly reduces the fluorescence quantum yield of many ssDNA-SWCNTs by as much as 90 percent. This reduction in fluorescence quantum yield is accompanied by a change in structure of the ssDNA corona, caused by reduced screening of the negatively charged phosphate backbone. We demonstrate that the effect on SWCNT optical properties is caused by oxidation of the nanotube sidewall via the reaction of protons with adsorbed oxygen, and is influenced by the ability of the ssDNA wrappings to amplify the local pH surrounding the nanotube at different salt concentrations. Moreover, we develop a reaction model to describe the ionic strength-dependent photoluminescence data characterized by two states at high (&gt; 200 mM) and low (&lt; 2 mM) monovalent salt concentration. Finally, the influence of ionic strength on structural and optical properties is influenced by the ssDNA sequence wrapping the nanotube, enabling the creation of ssDNA-wrapped SWCNTs whose optical properties are invariant with solution ionic strength.

Ionic strength mediated phase transitions of adsorbed DNA on single-walled carbon nanotubes

255th National Meeting (2018)

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