There is much interest in developing synthetic analogues of biological membrane channels1 with high efficiency and exquisite selectivity for transporting ions and molecules. Bottom-up2 and top-down3 methods can produce nanopores of a size comparable to that of endogenous protein channels, but replicating their affinity and transport properties remains challenging. In principle, carbon nanotubes (CNTs) should be an ideal membrane channel platform: they exhibit excellent transport properties4,5,6,7,8 and their narrow hydrophobic inner pores mimic structural motifs typical of biological channels1. Moreover, simulations predict that CNTs with a length comparable to the thickness of a lipid bilayer membrane can self-insert into the membrane9,10. Functionalized CNTs have indeed been found to penetrate lipid membranes and cell walls11,12, and short tubes have been forced into membranes to create sensors13, yet membrane transport applications of short CNTs remain underexplored. Here we show that short CNTs spontaneously insert into lipid bilayers and live cell membranes to form channels that exhibit a unitary conductance of 70–100 picosiemens under physiological conditions. Despite their structural simplicity, these ‘CNT porins’ transport water, protons, small ions and DNA, stochastically switch between metastable conductance substates, and display characteristic macromolecule-induced ionic current blockades. We also show that local channel and membrane charges can control the conductance and ion selectivity of the CNT porins, thereby establishing these nanopores as a promising biomimetic platform for developing cell interfaces, studying transport in biological channels, and creating stochastic sensors.
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Parts of this work were supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (characterization and transport studies), and the LDRD programme at LLNL, 12-ERD-073 (synthesis). R.T. acknowledges support from the LSP programme at LLNL. D.M. acknowledges support from an ROTC summer fellowship. V.A.F. acknowledges partial support by the Spanish Ministry of Economy and Competitiveness, grant BFU2012-34885, co-financed with European FEDER funds, and the Basque Government, grant IE12-332. Work at LLNL was performed under the auspices of the US Department of Energy under contract DE-AC52-07NA27344. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract DE-AC02-05CH11231.
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Biophysical Reviews (2018)