Nanoprecipitation-assisted ion current oscillations

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Nanoscale pores exhibit transport properties that are not seen in micrometre-scale pores, such as increased ionic concentrations inside the pore relative to the bulk solution, ionic selectivity and ionic rectification. These nanoscale effects are all caused by the presence of permanent surface charges on the walls of the pore. Here we report a new phenomenon in which the addition of small amounts of divalent cations to a buffered monovalent ionic solution results in an oscillating ionic current through a conical nanopore. This behaviour is caused by the transient formation and redissolution of nanoprecipitates, which temporarily block the ionic current through the pore. The frequency and character of ionic current instabilities are regulated by the potential across the membrane and the chemistry of the precipitate. We discuss how oscillating nanopores could be used as model systems for studying nonlinear electrochemical processes and the early stages of crystallization in sub-femtolitre volumes. Such nanopore systems might also form the basis for a stochastic sensor.

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Figure 1: Nanoprecipitation of calcium hydrogen phosphate (CaHPO4) in a single conical nanopore.
Figure 2: Ion current oscillations through a single conical nanopore induced by CaHPO4 nanoprecipitates.
Figure 3: Nanoprecipitation of cobalt hydrogen phosphate (CoHPO4) in a single nanopore.
Figure 4: Nanoprecipitation of magnesium hydroxide (Mg(OH)2) in a single nanopore.
Figure 5: Scheme of the transient formation of the nanoprecipitates.
Figure 6: Influence of biomolecules on the signature of the ion current oscillations recorded in 0.1 M KCl, 0.2 mM CoCl2 and 2 mM pH 8 phosphate buffer.


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Irradiation with swift heavy ions was performed at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. We thank the Alfred P. Sloan Foundation, the IM-SURE undergraduate programme, the Institute for Surface and Interface Science and the Institute for Complex Adaptive Matter for financial support.

Author information

Z.S., R.S.E. and I.V. conceived the experiments. M.R.P., M.S. and I.V. performed the experiments. D.C. analysed the data and was in charge of calculations. M.R.P. and Z.S. wrote the manuscript. R.S. co-wrote the manuscript. O.S. and C.C.M. analysed the data, discussed the results, explained the transient character of precipitation formation, and co-wrote the manuscript.

Correspondence to Zuzanna S. Siwy.

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Powell, M., Sullivan, M., Vlassiouk, I. et al. Nanoprecipitation-assisted ion current oscillations. Nature Nanotech 3, 51–57 (2008) doi:10.1038/nnano.2007.420

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