Pathway-Dependent Structures of DNA-Wrapped Carbon Nanotubes: Direct Sonication vs Surfactant/DNA Exchange

Abstract

DNA/single-wall carbon nanotube (SWCNT) hybrids have attracted significant interest due to their ability for SWCNT separation and their use as promising agents in biosensing and bioimaging applications. In order to perform such SWCNT separation and for application development, special DNA sequences are needed that have an ability to recognize specific chiral SWCNT. So far, sequence screening has relied on various sorting methods which are costly and time-consuming. Recently, a simple new and rapid way to produce DNA-SWCNT hybrids was reported using replacement of strong surfactant on SWCNT by DNA, aided by methanol. However, little is known about the nature of the exchange mechanism. Here, we investigated the kinetics of the process of replacing surfactant by DNA, aided by methanol. We propose a mechanistic model to analyze and extract the activation energy of the exchange process. We find that some recognition sequences have significantly different activation energies for different species of SWCNTs, while some sequences do not. Hybrids obtained via the surfactant replacement route were compared with those obtained by direct sonication using aqueous two-phase (ATP) separation and photoluminescence (PL) spectroscopy. We found that hybrids obtained by the two routes show the same separability as well as PL spectra for some sequences, but not for some other sequences. Thus, it appears that the replacement process does not always produce the same structure of DNA-SWCNT as produced by traditional direct sonication. Taking all the experimental findings into consideration, we propose a free energy diagram for DNA-SWCNT hybrid formation by surfactant replacement.