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Voltage-Gating in Synthetic Nanopores Induced by Cobalt Ions

Explore how cobalt ions impact voltage-gating in synthetic nanopores and its future applications, prepared by undergraduate Michael Sullivan from George Mason University under Dr. Zuzanna S. Siwy's mentorship at the University of California, Irvine.

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Voltage-Gating in Synthetic Nanopores Induced by Cobalt Ions

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  1. Voltage-Gating in Synthetic Nanopores Induced by Cobalt Ions Michael Sullivan, Undergraduate: George Mason University IM SURE Fellow, 2006 Dr. Zuzanna S. Siwy, Professor and Mentor: Department of Physics and Astronomy, University of California, Irvine Matthew R. Powell & Eric Kalman, Graduate Students: University of California, Irvine

  2. Outline • Motivation for Studies of Single Nanopores • Preparation, Behavior of Single Nanopores • The Impact of Cobalt • Conclusions and Future Applications

  3. Motivation • Small scale offers fundamental insight into physics on the nanoscale.

  4. Motivation • Structure models biological channels.

  5. Linear accelerator UNILAC, GSI Darmstadt, Germany Polyethylene terephthlalate(PET), Hostaphan, RN12 Preparing Single Nanopores

  6. Preparing Single Nanopores track Linear accelerator UNILAC, GSI Darmstadt, Germany • Heavy ions (e.g. Pb, Au, U) are fired with total kinetic energy equivalent to ~10% velocity of light • 1 Heavy Ion → 1 Latent Track → 1 Pore

  7. Preparing Conical Pores • Pores made conical through chemical etching. Latent Track Conical Pore D → L = 12 µm d

  8. Cylindrical Pore Conical Pore D → L = 12 µm d d >> Why Conical?

  9. Why Conical? • Asymmetry induces interesting reactions and interactions. • Rectifies Ion Current • Under equal but opposite electrochemical potentials, allow more ions to flow in the direction of d→D than D→d. • Biological channels are asymmetrical.

  10. Neutralization HCOOH + OH-  HCOO- + H2O One-Sided Etching Technique that We Used PET Stopping medium 1 M KCl + 1 M HCOOH Etch solution 9 M NaOH PET

  11. Voltage Applied Here Voltage Applied Here I U 0.1 M KCl 0.1 M KCl K+ Ion Transfer with + Applied Voltage K+ Ion Transfer with - Applied Voltage Recording Ion Current

  12. PET Film Working Electrode Ground Recording Ion Current The Conductivity Cell

  13. Recording Ion Current The Data Acquisition Setup Molecular Devices, Inc.

  14. I2 I1 • I1 > I2 because of Ion Current Rectification

  15. Recording Ion Current Time Series (I-t Curves) • Identical setup to I-V Curves, but current is read over time. • Useful when current is voltage dependent, yet not constant over time.

  16. I-t Readings w/o Cobalt +500 mV -100 mV -600 mV -1000 mV

  17. I-t Readings w/ Cobalt +500 mV -100 mV -600 mV -1000 mV

  18. 0.1 M KCl + 0.1 mM Co2+ @ -1V

  19. I-V Curves for Cobalt Concentrations

  20. Quantitative Qualitative Differences Between Pores Both w/ 0.1 M KCl + 0.1 mM Co2+@ -1000 mV • Different Timescales • Different Magnitudes • Same “Shape”

  21. Future Applications • Different divalent cations produce different characteristic responses: • Possible application for sensing molecules. 0.1 M KCl + 0.1 mM Ca2+ 0.1 M KCl + 0.1 mM Co2+

  22. Future Work • Needed: A mathematical model Koper, Sluyters. J. Electroanal. Chem. 303 (1990) 73.

  23. Acknowledgements • Thank you to the following people and organizations for making this experience possible: • My mentor, Zuzanna S. Siwy • My graduate students, Matt Powell and Eric Kalman • UROP and the IM-SURE Program • National Science Foundation

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