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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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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


Preamble fabrication of ion track conical nanopores
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)


Preamble fabrication of ion track conical nanopores1

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


Preamble diode like behavior of the conical nanopore in electrolyte solutions
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


Preamble single nanopores as resistive pulse sensors for biological molecules
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."


Motivation
Motivation: biological molecules

  • 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


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


Experimental
Experimental ion-irradiated polymer foils

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)


Experimental fabrication of nanopores with asymmetric profile
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


Experimental1
Experimental profile

Surfactant:

Dowfax 2A1 (sodium dodecyl diphenyloxide disulfonate)

- Why?

Easily soluble in alkaline solutions

Stable in alkaline solutions


Experimental control over the pore profile by etching conditions
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


Asymmetric pores with highly tapered profile
Asymmetric pores with highly-tapered profile conditions

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


Asymmetric pores with highly tapered profile1
Asymmetric pores with highly-tapered profile conditions

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


H ighly tapered pore profile current voltage characteristics of a many pore membrane
H conditionsighly-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


Rectification ratio for highly tapered pores dependence on electrolyte concentration
Rectification ratio for highly-tapered pores conditionsDependence on electrolyte concentration

~50 nm

~70 nm

~100 nm

5 min etching

6.5 min etching

8 min etching


Slight conditionsly-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


Rectification ratio i 1v i 1v depending on pore size and pore profile
Rectification ratio conditionsI (-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


Comparison with theoretical predictions conditions

(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


Fabrication of asymmetric ion track nanopores using asymmetric surfactant assisted etching
Fabrication of asymmetric ion track nanopores using asymmetric surfactant-assisted etching

PETor polycarbonate foil

Temperature 60oC

3 M NaOH

(6-10) M NaOH

+ surfactant


Shape ion track nanopores produced by asymmetric surfactant assisted etching
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


Conclusions
Conclusions surfactant-assisted etching

  • 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


Acknowledgements
Acknowledgements surfactant-assisted etching

P.Ramirez

(UP, Valencia)

A. Presz

(INCT, Warsaw)

R. Neumann

B. Schiedt

R. Spohr

C. Trautmann

(MR group GSI)


Thank you! surfactant-assisted etching


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