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24 th ICNTS Bologna, September 2

24 th ICNTS Bologna, September 2. Asymmetric ion track nanopores with highly-tapered profile: geometrical and current-voltage characteristics P.Yu. Apel 1 , I.V. Blonskaya 1 , S.N. Dmitriev 1 , O.L. Orelovitch 1 , B.A. Sartowska 2

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24 th ICNTS Bologna, September 2

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  1. 24th ICNTS Bologna, September 2 Asymmetric ion track nanopores with highly-tapered profile: geometrical and current-voltage characteristics P.Yu. Apel1, I.V. Blonskaya1, S.N. Dmitriev1, O.L. Orelovitch1, B.A. Sartowska2 1Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Joliot-Curie str. 6, 141980 Dubna, Russia 2Institute of Nuclear Chemistry and Technology, Dorodna str. 16, 03-195, Warsaw, Poland

  2. Preamble. Fabrication of ion track conical nanopores Irradiation with single ions at UNILAC (GSI) Sample in which single ion track is produced R. Spohr; German Patent DE 2951376 C2 (filed 20.12.1979, issued 15.09.1983); United States Patent No. 4369370 (1983)

  3. I Preamble. Fabrication of ion track conical nanopores Electrical field assisted one-sided chemical etching Electrical current registered after breakthrough PETfoil U + Acidic solution NaOH Apel P.Yu, Korchev E.Y., R.Spohr, Z.Siwy, M.Yoshida. Nucl. Instrum. Meth. B184 (2001) 337

  4. Preamble. Diode-like behavior of the conical nanopore in electrolyte solutions U I The pore walls are negatively charged due to COO- groups KCl KCl I (nA) The pore tip is cation-selective U (V) pH3 Ion-track asymmetric nanopores resemble properties of biological ion channels Transport properties of the asymmetric nanopores are determined by the size and shape of the narrow tip pH8

  5. Preamble. Single nanopores as resistive-pulse sensors for biological molecules Translocation of single-stranded DNA through the alpha-hemolysin channel Principle of the method "This translocation of DNA movie was made by Dr. Alek Aksimentiev using VMD and is owned by the Theoretical and Computational Biophysics Group, NIH Resource for Macromolecular Modeling and Bioinformatics, at the Beckman Institute, University of Illinois at Urbana-Champaign."

  6. Motivation: • Asymmetric nanopores as models of non-cylindrical channels, including biological ion channels • Asymmetric nanopores for molecular sensors (resistive-pulse technique) • Asymmetric nanopores for micro- and nanofluidics Goals of this work: • Development of methods allowing control over the shape of ion track nanopores • Study of geometrical and transport properties of nanopores having different profiles

  7. Surfactant-controlled etching of profiled pores in ion-irradiated polymer foils Surfactant molecules have a size of a few nanometers and block entrances of the “new-born” track pores The ratio between the alkali diffusion flux and the surfactant diffusion flux determines the profile

  8. Experimental Polymer foils: Polyethylene terephthalate (PET) Hostaphan 5, 12 and 23 um thick Irradiation with Kr ions (250 MeV), U-400 cyclotron Track densities 104-105 cm-2 Track densities 107- 3109 cm-2 Etching and subsequent measurement of ionic conductance in KCl solutions Conductometric cell with Ag/AgCl electrodes Etching and subsequent SEM and FESEM studies of pore structure JSM-840 (SEM) LEO-1530 (FESEM)

  9. Experimental. Fabrication of nanopores with asymmetric profile Latent track PET Photo-oxidized layer NaOH + surfactant Treatment with UV 280 nm <  < 400 nm, 7 W/m2 on the sample surface; exposure time: 24 h

  10. Experimental Surfactant: Dowfax 2A1 (sodium dodecyl diphenyloxide disulfonate) - Why? Easily soluble in alkaline solutions Stable in alkaline solutions

  11. Experimental. Control over the pore profile by etching conditions Highly-tapered pore profile 6M NaOH + 0.05% Dowfax, 60oC Slightly-tapered pore profile 3M NaOH + 0.05% Dowfax, 60oC

  12. Asymmetric pores with highly-tapered profile Kr ions, 5x107 cm-2, etched in6M NaOH+ 0.05% Df, 60oC, 5 min PET foil 5 um thick PET foil 12 um thick Surface pre-treated with UV Apel P.Yu., Blonskaya I.V., Dmitriev S.N., Orelovitch O.L., Sartowska B. Nanotechnology, 2007, 18, 305302

  13. Asymmetric pores with highly-tapered profile FESEM image of the pore tip (cross-section) d = 30-50 nm PET 12 um thick, Kr ions, 5x107 cm-2, 6M NaOH+ 0.05% Df 5 min etching   18o

  14. Highly-tapered pore profileCurrent-voltage characteristics of a many-pore membrane PET 23um 84Kr n=5e4 cm-2 6M NaOH+ 0.05%DF, 600C, 5 min one-sided UV 24 hours Well-pronounced rectification, especially high in 0.1M KCl The rectification is observed even for tip radii considerably larger than Debye length D = (о RT / 2 F2Co)1/2 which is equal to ~ 1 nm in0.1 М KCl

  15. Rectification ratio for highly-tapered poresDependence on electrolyte concentration ~50 nm ~70 nm ~100 nm 5 min etching 6.5 min etching 8 min etching

  16. Slightly-tapered pore profileCurrent-voltage characteristics for a many-pore membrane, normalized to one pore PET 23um 84Kr n=5e4 cm-2 3M NaOH+ 0.05%DF, 600C, 8 min one-sided UV 24 hours Small rectification! d = 25 nm 500 nm D 120 nm

  17. Rectification ratio I (-1V)/I(+1V) depending on pore size and pore profile 100 nm Effective pore diameter = diameter of a cylindrical pore having the same electrical conductance in 1M KCl

  18. Comparison with theoretical predictions (based on the Poisson and Nernst-Planck eqs) Trumpet-like pores: low rectification ratio Bullet-like pores: high rectification ratio d = 4 nm d = 4 nm (P.Ramirez, P.Yu.Apel, J.Cervera, S.Mafe. Nanotechnology 19 (2008) 315707) Qualitatively, experimental data on rectification are in agreement with theoretical prediction for nanopores with different shapes of the tip Quantitatively, the theory does not predict such a high rectification effect for the bullet-like pores with d = 30-70 nm

  19. Fabrication of asymmetric ion track nanopores using asymmetric surfactant-assisted etching PETor polycarbonate foil Temperature 60oC 3 M NaOH (6-10) M NaOH + surfactant

  20. Shape ion track nanopores produced by asymmetric surfactant-assisted etching Etching conditions: Upper surface: 3 M NaOH + surf. Bottom surface: 8 M NaOH Pore length = 5 um Small pore diameter  50 nm Large pore diameter  900 nm Remark: surprisingly, such pores show low rectification of electrical current

  21. Conclusions • New procedures for the production of ion-track asymmetrical nanopores in polymer foils are suggested: • - asymmetric photooxidation and symmetric surfactant-assisted etching; • - asymmetric surfactant-assisted etching • The methods allow control of pore profile and enable us to fabricate asymmetric nanopores other than conical • Ionic transport through the asymmetric pores strongly depends on the shape of the narrow tip • Rectification produced by highly-tapered nanopores is higher than theoretically predicted • Rectification is maximum at an electrolyte concentration of about 0.1 mol/L, i.e. close to the salt concentration in human body

  22. Acknowledgements P.Ramirez (UP, Valencia) A. Presz (INCT, Warsaw) R. Neumann B. Schiedt R. Spohr C. Trautmann (MR group GSI)

  23. Thank you!

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