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Anomalous ion transport in 2-nm hydrophilic nanochannels

Abstract

Transmembrane proteins often contain nanoscale channels through which ions and molecules can pass either passively (by diffusion) or actively (by means of forced transport). These proteins play important roles in selective mass transport and electrical signalling in many biological processes. Fluidic nanochannels that are 1–2 nm in diameter act as functional mimics of protein channels, and have been used to explore the transport of ions and molecules in confined liquids1,2,3. Here we report ion transport in 2-nm-deep nanochannels fabricated by standard semiconductor manufacturing processes. Ion transport in these nanochannels is dominated by surface charge until the ion concentration exceeds 100 mM. At low concentrations, proton mobility increases by a factor of four over the bulk value, possibly due to overlapping of the hydrogen-bonding network of the two hydration layers adjacent to the hydrophilic surfaces. The mobility of K+/Na+ ions also increases as the bulk concentration decreases, although the reasons for this are not completely understood.

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Figure 1: A 2-nm nanochannel device.
Figure 2: Epifluorescence images of Rhodamine 6G solution in nanochannel devices.
Figure 3: Conductance of HCl, KCl and NaCl at concentrations from 0.1 µM to 1 M.
Figure 4: Ionic concentration and mobility for 2-nm nanochannels.

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Acknowledgements

The authors thank Y.-F. Chen and D.-K. Kim for their help in conductance measurements and model development. The authors also thank P. Yang and H. Daiguji for continued collaboration in nanofluidics. This work was supported by Basic Energy Sciences, the Department of Energy (DE-AC02-05-CH11231), Center for Scalable and Integrated Nanomanufacturing (SINAM, DMI-0327077) and Center of Integrated Nanomechanical Systems at University of California, Berkeley (COINS, NSF EEC-0425914). Devices were fabricated at the Microfabrication Laboratory at the University of California, Berkeley.

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C.D. and A.M. conceived and designed the experiments. C.D. performed the experiments and analysed the data. C.D. and A.M. co-wrote the paper.

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Correspondence to Arun Majumdar.

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The authors declare no competing financial interests.

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Duan, C., Majumdar, A. Anomalous ion transport in 2-nm hydrophilic nanochannels. Nature Nanotech 5, 848–852 (2010). https://doi.org/10.1038/nnano.2010.233

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