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Position 1. 200. 150. Current (pA). 100. 50. breakthrough. 0. 242. 244. 246. 248. 250. 252. Time (min). Position 2. D. I (nA). 12. pH 7. 8. pH 5. 4. pH 2. d. - 400. 400. U (mV). : flux D i : diffusion coefficient z i : charge number

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Position 1

200

150

Current (pA)

100

50

breakthrough

0

242

244

246

248

250

252

Time (min)

Position 2

D

I(nA)

12

pH 7

8

pH 5

4

pH 2

d

- 400

400

U(mV)

: flux

Di: diffusion coefficient

zi : charge number

e : dielectric permittivity of solution

of ionic species i

Continuity equations

asymmetric etching

metal mask

foil

I

V

stopping solution

etchant

Transference number t:

  • measure for selectivity

  • obtained from Vrev

Explanation:

  • Pore tip has biggest influence on transport characteristics

  • Charges less screened by low concentrations

  •  biggest influence of charges for low c on tip side

Track-etched nanopores:

from theory to application

Contact: Birgitta Schiedt: [email protected]

B. Schiedt1, A. Alcaraz2, M. Ali3, V. Bayer1, J. Cervera2, W. Ensinger3, K. Healy4,S. Mafé5,A.P. Morrison4,R. Neumann1, P. Ramírez6,

1Gesellschaft für Schwerionenforschung (GSI), Planckstr. 1, D-64291 Darmstadt, Germany

2Dept. de Ciències Experimentals. Universitat Jaume I. Apdo. 224, E-12080 Castelló, Spain

3 Darmstadt University of Technology, Department of Materials Science Petersenstraße 23, D-64287 Darmstadt, Germany

4 Dept. of Electrical and Electronic Engineering, University College Cork, Ireland

5 Dept. de Termodinàmica, Universitat de València, E-46100 Burjassot, Spain

6Dept. de Física Aplicada. Univ. Politècnica de València. Camino de Vera s/n, E-46022 Valencia, Spain

Motivation Conical nanopores in polymer films show interesting ionic transport properties (rectification, selectivity) [1][2] and have potential applications in single molecule detection and analysis [3]. For these applications to be successful, it is essential to have a good understanding of the nanopore system itself, and to explore modifications and extensions.

The nanopores

Material:PET and Polyimide

12 µm thickness

Production:

  • Irradiation with heavy ions (U, Au Pb)

  • Track - etching

Geometry:

(used here)

Properties: negatively charged surface (COO-)

a conical pores rectify ion current,

depending on pH and concentration

of electrolyte

  • 1 pore per membrane

  • conical

  • D = 0.5 – 1.5 µm, d = 5-50 nm

Understanding ionic transport:

PNP modelling [4]

Production of conical pores [1]

1. Irradiation

with single heavy ions (U, Au, Pb)

2.Controlled Etching

from one side

Nernst-Planck equations

Poisson equation

Method:

calculate concentration and potential profiles atVRT (fL – fR) /F

a average potential and concentration profiles

a average ionic fluxes

To fit data: surface charge is the only free parameter

I-V curves can be reproduced semiquantitatively

Potential profiles

Experiment

Theory

Permselectivity [5]

Principle: concentrationgradient

potential difference(Vrev)

shift in I-V curve

Modify transport properties by chemical surface modification [6]

  • Trasport properties of the pores are strongly influenced by surface charge

  • Coupling method may also be used to attach biomolecules

Idea:

Method:

1

1. 0.2 M NHS, 0.1 M EDC, aq.

10 h

2. 0.1 M EDA, aq.

8 h

3. SA saturated, ethanol

8 h

Results:

Reversal potential depends on direction of concentration gradient

 selectivity higher for low concentration on pore tip

2

3

Reversal potential

Transference number

Results: Success is demonstrated by I-V curves (all measurements 0.1 M KCl)

PNP

experiment

Pore: Polyimide, d ~ 64 nm, D ~ 1.6 µm

PNP

unmodified

modified with EDA

modified with SA

1

2

3

experiment

-NH3+/COO-

-COO-

-COO-

-NH3+

-COOH

-COOH

[1] P.Y. Apel, Y.E. Korchev, Z. Siwy, R. Spohr, M. Yoshida,Nucl. Inst. Meth. B184, 337 (2001)

[2] Z. Siwy and A. Fuliński, Am. J. Phys.72, 567 (2004)

[3] A. Mara, Z. Siwy, C. Trautmann, J. Wan and F. Kamme, Nano Lett.4, 497 (2004)

[4] J. Cervera et al., J. Chem. Phys.124, 104706 (2006)

[5] J. Cervera et al.,J. Phys. Chem. C111, 33, 12265 (2007)

[6] M. Ali et al. GSI Annual Report20061, 323 (2007)


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