Understanding carbon nanotube channel formation in the lipid membrane

Abstract

Carbon nanotubes (CNTs) have been considered a prominent nano-channel in cell membranes because of their prominent ion-conductance and ion-selectivity, offering agents for a biomimetic channel platform. Using a coarse-grained molecular dynamics simulation, we clarify a construction mechanism of vertical CNT nano-channels in a lipid membrane for a long period, which has been difficult to observe in previous CNT-lipid interaction simulations. The result shows that both the lipid coating density and length of CNT affect the suitable fabrication condition for a vertical and stable CNT channel. Also, simulation elucidated that a lipid coating on the surface of the CNT prevents the CNT from burrowing into the lipid membrane and the vertical channel is stabilized by the repulsion force between the lipids in the coating and membrane. Our study provides an essential understanding of how CNTs can form stable and vertical channels in the membrane, which is important for designing new types of artificial channels as biosensors for bio-fluidic studies.

Nanoporous Membranes of Densely Packed Carbon Nanotubes Formed by Lipid-Mediated Self-Assembly

“…This behavior is expected from previous simulations. , In experiments, CNTs are usually coated by detergents or lipids. These coatings might prevent tilting and reduce the sensitivity of the assembly process to the length of the CNT. , In the simulations, the shortest CNTs did not form stable clusters. Lipids bent over them and destroyed the order needed for controlled assembly (Figures B and S5).…”

“…We expect the most important solvent properties to be hydrophobicity and viscosity. An overly hydrophobic solvent could prevent the CNTs from inserting into the membrane while adding lipid coating or lipid-like detergents could facilitate the insertion process. , According to the Saffman-Delbrück law, the viscosity of the fluid has an influence on the diffusivity of the membrane inclusions and thus influences cluster formation. A more viscous fluid slows down CNT diffusion but the dominant factor is the membrane viscosity, as we had shown in earlier work …”

“…As a key requirement, CNTs have been successfully introduced into lipid vesicles. − CNTs can be pushed into or through lipid membranes, , but they can also be internalized by passive diffusion − or by growing bilayer structures around CNTs from dispersed solution . The amount of lipid coating plays a major role in the formation of transmembrane channels with nonfunctionalized CNTs . Coarse-grained as well as atomistic simulations , have shown that the equilibrium orientation of open CNTs in a membrane strongly depends on their lengths and the chemical functionalization of their ends.…”

“… 25 The amount of lipid coating plays a major role in the formation of transmembrane channels with nonfunctionalized CNTs. 26 Coarse-grained as well as atomistic simulations 13 , 27 have shown that the equilibrium orientation of open CNTs in a membrane strongly depends on their lengths and the chemical functionalization of their ends. Polar end-functionalizations keep the nanotube in an up-right orientation and prevent short pores from becoming blocked by lipid head groups.…”

Molecular Dynamics of Water Embedded Carbon Nanocones: Surface Waves Observation

“…Pristine carbon nanotubes serve as prototypes for analogous nanosized cylindrical pore channels subjected to surface functionalisation and decoration [34,35]. They are used regularly to predict how these compounds behave either when they are solvent exposed to membrane substrates or embedded in bilayer environments and polymer matrices [36][37][38][39][40]. Today, CNTs are compared to biological porins and biomimetic (artificial) water channels which undergo structural deformations such as spatial variations of the pore size and shape [41][42][43][44][45][46].…”