Asymmetric ion track nanopores with highly-tapered profile: geometrical and current-voltage...
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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)