A Low Energy Route to DNA-wrapped Carbon Nanotubes via Replacement of Bile Salts
Ming Zheng, Jason K. Streit, Jeffrey A. Fagan
DNA-wrapped carbon nanotubes are a class of bio-nano hybrid molecules that exhibit extended bonding structures and have enabled carbon nanotube sorting, controlled assembly, and biosensing and bioimaging applications. The current method of synthesizing these hybrids via direct sonication of DNA/nanotube mixtures is time consuming and not suitable for high throughput synthesis and sequence screening. In addition, the direct sonication method cannot make use of nanotubes presorted by various surfactant-based methods, and cannot maintain preformed secondary and tertiary structure inherent in many DNA sequences. Here, we report a simple, quick, and robust process to replace a strong binding bile salt surfactant coating on nanotubes by arbitrary single-stranded DNA sequences. The process calls for sequential addition of a water-soluble polymer and DNA to surfactant-dispersed nanotubes, and titration of methanol into the aqueous mixture to simultaneously reduce surfactant binding and promote DNA wrapping. The newly formed DNA-wrapped nanotubes and excess free DNA are then isolated from the reaction mixture by isopropanol precipitation. The entire process can be completed within 10 min and converts over 90% nanotubes into the DNA wrapped form. Applying the exchange process to nanotubes pre-sorted by surfactant-based methods, we show that the resulting DNA-wrapped carbon nanotubes can be further sorted to yield nanotubes with defined handedness, helicity, and endohedral filling. The exchange method greatly expands the structural and functional variety of DNA-wrapped carbon nanotubes, and opens possibilities for DNA-directed assembly of structurally-sorted nanotubes, and high throughput screening of properties that are controlled by the wrapping DNA sequences.
DNA, bile salt, single-wall carbon nanotubes, separation, dispersion