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

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

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

Motivation Structure models biological channels.

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

Preparing Single Nanopores 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 track

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

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

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.

One-Sided Etching Technique that We Used Etch solution 9 M NaOH HCOOH + OH -  HCOO - + H 2 O Neutralization Stopping medium 1 M KCl + 1 M HCOOH PET

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

Recording Ion Current PET Film Ground Working Electrode The Conductivity Cell

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

I1I1 I2I2 I 1 > I 2 because of Ion Current Rectification

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.

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

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

0.1 M KCl mM Co -1V

I-V Curves for Cobalt Concentrations

Differences Between Pores Both w/ 0.1 M KCl mM Co mV Different Timescales Different Magnitudes Same “Shape” Quantitative Qualitative

Different divalent cations produce different characteristic responses: Possible application for sensing molecules. Future Applications 0.1 M KCl mM Co M KCl mM Ca 2+

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

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