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

24th ICNTSBologna, September 2

Preamble. Fabrication of ion track conical nanopores

Irradiation with single ions at UNILAC (GSI)

R. Spohr; German Patent DE 2951376 C2 (filed 20.12.1979, issued 15.09.1983); United States Patent No. 4369370 (1983)

Sample in which single ion track is produced

I

U

NaOHAcidic solution

PET foil

126 128 130 132 134

0

200

400

600

curr

ent (

pA)

time (min)

Apel P.Yu, Korchev E.Y., R.Spohr, Z.Siwy, M.Yoshida. Nucl. Instrum. Meth. B184 (2001) 337

+

Electrical current registered

after breakthrough

Electrical field assisted one-sided chemical etching

Preamble. Fabrication of ion track conical nanopores

Preamble. Diode-like behavior of the conical nanopore in electrolyte solutions

KCl KCl

UI

I (nA)

U (V)

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

The pore tip is cation-selective

The pore walls are negatively charged due

to COO- groups

pH3

pH8

Preamble. Single nanopores as resistive-pulse sensors for biological molecules

Translocation of single-stranded DNA through the alpha-hemolysin

channelPrinciple 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:

•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

The ratio between the alkali diffusion flux and the surfactant diffusion flux determines the profile

Surfactant molecules have a size of a few nanometers and block entrances of the “new-born” track pores

ExperimentalPolymer 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

Etching and subsequent measurement of ionic conductance in KCl solutions

Conductometric cell with Ag/AgCl electrodes

Track densities 107- 3109 cm-2

Etching and subsequent SEM and FESEM studies of pore structure

JSM-840 (SEM)

LEO-1530 (FESEM)

Treatment with UV

PET

Latent track

Photo-oxidized layer

Experimental. Fabrication of nanopores with asymmetric profile

NaOH + surfactant

280 nm < < 400 nm, 7 W/m2 on the sample surface; exposure time: 24 h

Experimental

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

6M NaOH + 0.05% Dowfax, 60oC

Highly-tapered pore profile

Slightly-tapered pore profile

3M NaOH + 0.05% Dowfax, 60oC

Asymmetric pores with highly-tapered profileKr ions, 5x107 cm-2, etched in 6M NaOH + 0.05% Df, 60oC, 5 min

Surface pre-treated with UV

PET foil 5 um thick PET foil 12 um thick

Apel P.Yu., Blonskaya I.V., Dmitriev S.N., Orelovitch O.L., Sartowska B. Nanotechnology, 2007, 18, 305302

FESEM image of the pore tip (cross-section)

d = 30-50 nm

18o

PET 12 um thick,

Kr ions, 5x107 cm-2,

6M NaOH + 0.05% Df

5 min etching

Asymmetric pores with highly-tapered profile

Highly-tapered pore profile

Current-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

-1.0 -0.5 0.0 0.5 1.0

-1000

-500

0

500

deff = 255 nm

0.01MKCl 0.1MKCl 1MKCl

U, V

I, A

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 in 0.1 М KCl

Rectification ratio for highly-tapered pores

Dependence on electrolyte concentration

-2 -1 00

2

4

6

8

10

12

14

16

rect

ifica

tion

ratio

at +

/- 1

V

logCKCl

-2 -1 00

2

4

6

8

10

12

14

16re

ctifi

catio

n r

atio

at +

/- 1

V

logCKCl

-2 -1 00

2

4

6

8

10

12

14

16

rect

ifica

tion

ratio

at +

/- 1

V

logCKCl

5 min etching 6.5 min etching 8 min etching

~50 nm ~100 nm~70 nm

Slightly-tapered pore profile

Current-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

-1.0 -0.5 0.0 0.5 1.0

-8

-6

-4

-2

0

2

4

U, V

0.01MKCl 0.1MKCl 1MKCl

deff= (.50*10-9*23*10-4/3.14/0.11/0.1)1/2=115 nm

I, nA

500 nm

d = 25 nm

D 120 nm

Small rectification!

0 100 200 300 400 5000

2

4

6

8

10

12

14

Electrolyte: 0.1 M KCl

Re

ctifi

catio

n r

atio

at 1

V

Effective pore diameter, nm

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

Comparison with theoretical predictions (based on the Poisson and Nernst-Planck eqs)

(P.Ramirez, P.Yu.Apel, J.Cervera, S.Mafe. Nanotechnology 19 (2008) 315707)

Trumpet-like pores: low rectification ratio Bullet-like pores: high

rectification ratio

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

d = 4 nm

d = 4 nm

3 M NaOH(6-10) M NaOH

PET or polycarbonate foil

Fabrication of asymmetric ion track nanopores using asymmetric surfactant-

assisted etching

+ surfactant

Temperature 60oC

Shape ion track nanopores produced by asymmetric surfactant-assisted etching

Pore length = 5 umSmall pore diameter 50 nmLarge pore diameter 900 nm

Etching conditions:Upper surface: 3 M NaOH + surf.Bottom surface: 8 M NaOH

Remark: surprisingly, such pores show low rectification of electrical current

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

Acknowledgements

R. Neumann

B. Schiedt

R. Spohr

C. Trautmann

(MR group GSI)

A. Presz

(INCT, Warsaw)

P.Ramirez

(UP, Valencia)

Thank you!