Voltage-Controlled Purification of DNA-Wrapped Carbon Nanotubes

We report a novel method to trap preferentially and release DNA-wrapped single wall carbon nanotube (DNA/SWNT) hybrids both as a whole population and by chirality of the SWNT. The preferential trapping allows for enrichment of the initially polydisperse chiral population into its constituents. The separation system combines an HPLC, a potentiostat and a quartz crystal microbalance flow cell that was modified to allow for a standard three electrode setup. The combination of these devices allows for real time control over the working electrode surface potential, liquid flow rate and mobile phase concentration while monitoring adsorption/desorption mass on/from the working electrode and the eluting species' UV/Vis spectra. This method also has an advantage in that we can vary the coating upon the quartz crystal microbalance working electrode with non-conductive materials. This gives us more control over both the electrostatic and van der Waals/London dispersion interactions and a larger experimental parameter space to explore. Our results show that holding the surface potential at -900mV relative to an Ag/AgCl reference electrode can trap hybrids upon the microbalance surface. These trapped hybrids can be ejected back into solution via dropping the potential, adding salt, or accelerating the mobile phase flow rate. In numerous experiments we see that the injection population and the released population vary significantly in the resolution of SWNT chirality. Separation between metallic and semiconducting classes of SWNTs has been achieved. We report our most recent results fine tuning this method to isolate purified SWNT chiralities.