Research ArticleAPPLIED SCIENCES AND ENGINEERING

Biomimetic potassium-selective nanopores

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Science Advances  08 Feb 2019:
Vol. 5, no. 2, eaav2568
DOI: 10.1126/sciadv.aav2568
  • Fig. 1 Designing potassium-selective solid-state nanopores.

    (A) Single nanopores with a tunable opening diameter were created in 30-nm-thick silicon nitride films by the process of dielectric breakdown. The first modification step led to the attachment of carboxyl groups. The second modification involved either symmetric attachment of 4′-aminobenzo-18-crown-6 ether (B) or asymmetric modification with the crown ether and ssDNA (C). (B) I-V curves in 1 M KCl and 1 M NaCl recorded for a 1-nm-diameter pore whose walls were decorated with crown ether, as shown in the scheme. The graph on the right summarizes ratios of currents in KCl and NaCl at 1 V before and after each modification step for the same nanopore. Ratios of currents for the nanopore before and after carboxylation are calculated on the basis of the recordings in 100 mM of the salts. (C) I-V curves in 1 M KCl and 1 M NaCl for a 0.6-nm-wide nanopore modified with crown ether and ssDNA. Selectivity of the nanopore is shown as ratios of ionic currents in KCl and NaCl solutions measured under the same conditions as in (B).

  • Fig. 2 Selectivity of nanopores toward potassium.

    (A) Experimental ratios of ion currents in KCl and NaCl solutions for six independently prepared nanopores subjected to chemical modification with crown ether (CE) and ssDNA. Data for three different bulk concentrations of the salts are shown. The model fit is shown as dashed lines. (B) Experimental data of potassium selectivity for three nanopores modified only with crown ether. SDs of currents for individual voltages are shown in I-V curves in Fig. 1 and fig. S5.

  • Fig. 3 Phenomenological model of the potassium selectivity of solid-state nanopores.

    (A) Scheme of the modeled system with geometrical parameters used in the model. (B) Diameter dependence of the selectivity sensitivity (mS) to voltage. mS is defined here as the slope of a linear fit of log(IK/INa) versus voltage for 1 M KCl and NaCl solution concentrations. (C) I-V curves at three different bulk KCl concentrations for the same pore shown in Fig. 1C. (D) I-V curves at three different bulk NaCl concentrations for the same pore as (C). Symbols are for experimental data, while dashed lines represent model predictions using the parameters listed in Table 1. SDs of currents for individual voltages are shown in I-V curves in fig. S5.

  • Fig. 4 Ion current measurements in mixtures of KCl and NaCl for a 1-nm-diameter nanopore modified with crown ether and DNA.

    (A) I-V curves in all conditions examined. (B) Ratio of the ionic currents in mixed salt solutions and in 1 M NaCl solution as a function of KCl concentration at +1 V and a constant total salt concentration of 1 M. The inset shows the magnitude of the ion current as a function of KCl concentration under the same conditions. Dashed lines show model predictions using the parameters given in Table 1 for a 1-nm-diameter pore.

  • Table 1 Values of parameters used to fit the experimental data of potassium selectivity and ion current values (Figs. 2 to 4).
    koff0,K
    (s−1)
    kon0,K
    (s−1 M−1)
    Embedded Image
    (M)
    koff0,Na
    (s−1)
    kon0,Na
    (s−1 M−1)
    Embedded Image
    (M)
    dce
    (nm)
    9.9 × 1085.1 × 1095.159.2 × 1061.1 × 10811.951.9

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/2/eaav2568/DC1

    Fig. S1. Examples of I-V curves for the nanopores shown in Fig. 1 before crown ether attachment.

    Fig. S2. Selectivity of nanopores shown in Fig. 1 toward potassium ions at −1 V.

    Fig. S3. Ion selectivity at 1 V of a nanopore modified with crown ether from one side only.

    Fig. S4. Ion current through a 1-nm-diameter nanopore modified with DNA from one side.

    Fig. S5. Ion currents through a nanopore shown in Fig. 1C as a function of KCl and NaCl concentrations.

    Fig. S6. Scheme of a modeling system used to predict local ionic concentrations and electric potential in a nanopore.

    Fig. S7. Results of numerical modeling of ionic concentrations and electric potential in a nanopore shown in fig. S6.

    Fig. S8. I-V curves for the nanopore shown in Fig. 4.

    Table S1. Pore opening diameters calculated according to Eq. 1 for all nanopores considered in the manuscript.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Examples of I-V curves for the nanopores shown in Fig. 1 before crown ether attachment.
    • Fig. S2. Selectivity of nanopores shown in Fig. 1 toward potassium ions at −1 V.
    • Fig. S3. Ion selectivity at 1 V of a nanopore modified with crown ether from one side only.
    • Fig. S4. Ion current through a 1-nm-diameter nanopore modified with DNA from one side.
    • Fig. S5. Ion currents through a nanopore shown in Fig. 1C as a function of KCl and NaCl concentrations.
    • Fig. S6. Scheme of a modeling system used to predict local ionic concentrations and electric potential in a nanopore.
    • Fig. S7. Results of numerical modeling of ionic concentrations and electric potential in a nanopore shown in fig. S6.
    • Fig. S8. I-V curves for the nanopore shown in Fig. 4.
    • Table S1. Pore opening diameters calculated according to Eq. 1 for all nanopores considered in the manuscript.

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