Research ArticleION PUMP

“Uphill” cation transport: A bioinspired photo-driven ion pump

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Science Advances  19 Oct 2016:
Vol. 2, no. 10, e1600689
DOI: 10.1126/sciadv.1600689
  • Fig. 1 From biological ion pump to bioinspired ion pump.

    The diagram at the top left corner is the natural proton pump (H+-ATPase) in plants and fungi. The proton pump transports H+ against concentration gradient to extracellular environment to maintain its acid environment, which is essential to the secondary transport process related to cellular chemical species exchange. The diagram at the bottom left corner refers to the natural sodium-potassium pump (Na+,K+-ATPase) in animals, and it can transport K+ and Na+ against their electrochemical gradient, which lay the foundation for many life processes, such as nerve conduction and muscle contraction. These two biological ion pumps are both implemented by coupling the uphill pumping process to an energy source, such as adenosine triphosphate (ATP). Inspired from various biological ion pumps, the bioinspired photo-driven ion pump system is shown at the right side. The single cation-selective PET nanochannel can pump cations from low concentration to high concentration under UV irradiation, which could be ascribed to the enhanced electrostatic interaction between the ions traversing the nanochannel and the charged groups (−COO) on the nanochannel wall. ADP, adenosine diphosphate; Pi, inorganic phosphate.

  • Fig. 2 Experimental observation of the pumping phenomenon.

    (A) The zero-volt currents of the single nanochannel (tip ≈ 10 nm) under asymmetric (Ct = 0.1 M; Cb = 0.075 M) electrolyte concentration recorded alternately in darkness and under UV irradiation. The zero-volt currents were recorded in different kinds of electrolyte solutions, including KCl (black squares), NaCl (maroon circles), and LiCl (gray triangles). (B) The relationship between the zero-volt currents and the concentration gradient (Cb/Ct) in darkness (black squares) and under UV irradiation (yellow-green circles). Ct remains at 0.1 M, and Cb gradually decreases from 0.09 to 0.01 M. The electrolyte solutions were KCl.

  • Fig. 3 Theoretical simulation of the pumping property.

    The simulation model is based on a 1000-nm-long conical nanochannel (tip, 10 nm; base, 250 nm). (A) Electrical potential profile along the axis of the PET nanochannel (base, x = 0 nm; tip, x = 1000 nm) when integrating asymmetric electrolyte concentration (Ct = 0.1 M; Cb = 0.075 M). The surface charge density of the inner wall is set to be 0.06 C/m2. There exists an obvious ΔV from the base to the tip. (B) As the surface charge density (σ) increases, the ΔV increases accordingly. (C) The cation concentration distributions along the axis of the PET nanochannel when integrating asymmetric electrolyte concentration (Ct = 0.1 M; Cb = 0.075 M). The surface charge density is set to two extreme values, −0.04 C/m2 (black) and −0.24 C/m2 (red), respectively, which represent two types of the cation migration directions. The concentration difference between the tip (x = 1000 nm) and the base (x = 0 nm) is defined as Ctb. (D) The relationship between the Ctb and the surface charge density. Ctb is inversed when the surface charge changes from −0.14 to −0.16 C/m2.

  • Fig. 4 Effect of the electrolyte (KCl) pH on the pumping property.

    (A) I-V curves of the single nanochannel (tip ≈ 6 nm) recorded in darkness (black) and under UV irradiation (yellow-green) when integrating asymmetric concentration (Ct = 0.1 M; Cb = 0.075 M) at different pH values. (B) Corresponding zero-volt currents in darkness (black columns) and under UV irradiation (yellow-green columns) recorded at different pH values.

  • Fig. 5 Effect of the charge polarity on the pumping property.

    (A) I-V curves of three kinds of single nanochannels (tip ≈ 12 nm) (square, platinum-sputtered neutral nanochannel; circle, EN-modified positively charged nanochannel; triangle, naked negatively charged nanochannel) recorded in darkness (black) and under UV irradiation (yellow-green) when integrating asymmetric electrolyte concentration (Ct = 0.1 M; Cb = 0.075 M) at pH 6.1. (B) Corresponding zero-volt currents in darkness (black columns) and under UV irradiation (yellow-green columns).

  • Fig. 6 Effect of light intensity and wavelength on the pumping property.

    The single nanochannel (tip ≈ 14 nm) is placed in asymmetric electrolyte concentration (Ct = 0.1 M; Cb = 0.075 M) at pH 6.1. (A) UV light with enough intensity can reverse the cation flow inside the nanochannel and promote the pumping process. The zero-volt current reached the maximum value at the light intensity of about 281 mW/cm2 (yellow-green circles). (B) The position of the maximum zero-volt current generation (313 nm) in our experiments is basically at the wavelength where the PET membrane shows a strong absorbance.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/10/e1600689/DC1

    Nanochannel fabrication

    Ionic current recordings

    The cycling performance

    Numerical simulation model

    fig. S1. Scheme of the etching setup.

    fig. S2. Schematic of the experimental conductivity cell.

    fig. S3. The cycling performance of the ion pump system.

    fig. S4. Numerical simulation model to investigate the pumping property.

  • Supplementary Materials

    This PDF file includes:

    • Nanochannel fabrication
    • Ionic current recordings
    • The cycling performance
    • Numerical simulation model
    • fig. S1. Scheme of the etching setup.
    • fig. S2. Schematic of the experimental conductivity cell.
    • fig. S3. The cycling performance of the ion pump system.
    • fig. S4. Numerical simulation model to investigate the pumping property.

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