Nanofluidics: Ionic Transport Properties of Surfactant-Stabilized Carbon Nanotube Porins (CNTPs), Chirality-controlled CNTPs and Partially-obstructed Fluorescent Ultrashort Carbon Nanotube Porins (FUNPs)

Carbon nanotube porins (CNTPs), short segments of carbon nanotubes stabilized by a lipid coating, are a promising example of artificial membrane channels that mimic a number of key behaviors of biological ion channels and promising model system to investigate the role of the electronic properties of the channel wall on ion transport.
   
   While the lipid-assisted synthesis of CNTPs may facilitate their subsequent incorporation into lipid bilayers, it limits the applicability of these pores in other self-assembled membrane materials and precludes the use of large-scale purified CNT feedstocks. Here I demonstrate that CNTPs can be synthesized by sonochemical cutting of long CNT feedstocks in the presence of different surfactants, producing CNTs with transport properties identical to those obtained by the lipid-assisted procedure.
   
   CNTs of different chiralities can be synthesized which are either metallic or semiconducting. Here, I studied short chirality-separated pure (6,5), (7,4), and (7,5)/(8,4) CNT porins (CNTPs), which vary in electronic properties, yet are almost identical in diameter. Single channel conductance from potassium ion transport through these CNT porins indicates that the electronic properties have a weak effect on ion transport.
   
   In addition to intrinsic electronic properties, I also investigated the role of the functional group and defects on the CNT wall. I measured potassium ion transport through fluorescent ultrashort carbon nanotube porins (FUNPs)– functionalized channels with single defined p-nitroaryl defect incorporated into its structure. These channels exhibited significantly lower ion conductance compared to the pure (6, 5) CNTPs regardless of the surfactant used to solubilize the CNTPs.
   
   Overall, my study highlights the role of the electronic properties of the CNTs, including defects, and functional groups, on the nanofluidic transport of ions through single channel CNTs.

Sidi Zhao is a PhD candidate in Materials and Biomaterials Science and Engineering at the University of California, Merced. She received her B.S. in Material Science and Engineering from Beijing University of Chemical Technology, Beijing, China, and her M.S. in Polymer Science from the University of Akron, OH, U.S. Her research interests lie in the field of nanomaterials and nanofluidics, focusing on ionic transport properties of carbon nanotube porins (CNTPs) with different electronic properties, defects, and functional groups. During her Ph.D., she did research at Lawrence Livermore National Laboratory (LLNL) in the Academic Cooperation Program and was the affiliate user of Lawrence Berkeley National Laboratory (LBL), Molecular Foundry. She is a graduate student member of the Center for Enhanced Nanofluidic Transport (CENT), an Energy Frontier Research Center (EFRC) from the U.S. Department of Energy (DOE).