Determination of the Charge Attached to Micro-scale Devices Used in Fluidic Self-Assembly Processes


Self-assembly of micron sized and smaller particles has previously been demonstrated using biologically inspired events such as DNA hybridization and interactions of ligands and receptors. In order to implement these techniques to create practical electronic devices, a quantitative measure of the amount of substance attached to the device surface just prior to the final assembly is essential. In the present investigation, this crucial quantity was investigated from the electrophoretic mobility of particles, which was ascertained by examining their motion under applied electric fields ranging from 0 to 1 V/mm. Sequential CCD camera images processed with custom software enabled calculation of particle velocities during their viscous motion in an inexpensive electrophoresis chamber filled with a low-conductivity buffer solution. A linear fit through the velocity vs. electric field data points yielded the electrophoretic mobility, which was utilized in the Stokes equation to calculate the net amount of charge present on each device. For 5.44 micron carboxyl-coated polystyrene beads, this method indicated a charge of 2.69e-15 C per particle. The manufacturer of the beads, Spherotech corporation, quoted 6.37e-11 C as the expected charge. The more than three orders of magnitude discrepancy is at least partially attributable to the electrophoretic retardation and relaxation effects of small electrolyte ions in the buffer solution. The method was also applied to silicon islands in the shape of a cone frustum with similar dimensions to the beads. A mercapto-ethane-sulfonate monolayer, attached via thiol bonds to the gold-coated surface of the islands, provided the charge. The amount of charge on an island was calculated to average 2.48e-15 C, corresponding to a density of 3.82e10 mercapto-ethane-sulfonate groups per square centimeter of Au surface.

This is a preview of subscription content, access via your institution.


  1. [1]

    R. Bashir, “Biologically Mediated Assembly of Artificial Micro and Nanostructures”, CRC Handbook of Nanoscience, Engineering, and Technology, edited by Goddard, Brenner, Iafrate, and Lyshevski. Chapter 15, 2003, CRC Press.

    Google Scholar 

  2. [2]

    Niemeyer, C. M., Ceyhan, B., Gao, S., Chi, L., Peschel, S. and Simon, U., Colloid Polymer Science, 279, 68, (2001).

    CAS  Article  Google Scholar 

  3. [3]

    Edelstein, R. L., Tamanaha, C. R., Sheehan, P. E., Miller, M. M., Baselt, D. R., Whitman L. J. and Colton, R. J., Biosensors & Bioelectronics, 14, 10, (2000).

    Article  Google Scholar 

  4. [4]

    Andres, R. P., Datta, S., Janes, D. B., Kubiak, C. P. and Reifenberger, R., in The Handbook of Nanostructured Materials and Nano-technology, (Academic Press, 1998).

    Google Scholar 

  5. [5]

    S.W. Lee, H.A. McNally, D. Guo, M. Pingle, D.E. Bergstrom, R. Bashir, Langmuir; 18 (8); 3383–3386, (2002).

    CAS  Article  Google Scholar 

  6. [6]

    Yeh, H. J. and Smith, J. S., IEEE Photonics Technology Letters, 6,6, p706, (1994).

    Article  Google Scholar 

  7. [7]

    E. Prohofsky, Statistical mechanics and stability of macromolecules: application to bond disruption, base pair separation, melting, and drug dissociation of the DNA double helix, Cambridge University Press, New York, NY, (1995).

    Google Scholar 

  8. [8]

    Methods in Enzymology, Edited by M. Wilcheck and E.A. Bayer, Vol.184, pp.3, (1990).

  9. [9]

    A. Ulman, Chem. Rev., 96(4), 1533–1554, (1996).

    CAS  Article  Google Scholar 

  10. [10]

    H. McNally, S.W. Lee, D. Guo, M. Pingle, D. Bergstrom, R. Bashir, Materials Research Society Symposium Proceedings, Vol.707, Fall 2002

  11. [11]

    Viscous Fluid Flow, 2nd Ed., Frank M. White, McGraw Hill, Boston, MA. 1991.

    Google Scholar 

  12. [12]

    Bier, M., in Electrohoresis: Theory, Method, and Applications, Academic Press, New York, NY 1967.

    Google Scholar 

  13. [13]

    Demers LM; Mirkin CA; Mucic RC; Reynolds RA; Letsinger RL; Elghanian R; Viswanadham G, Analytical Chemistry, V72,I22, p5535–5541 (2000).

    Article  Google Scholar 

Download references


We would like to acknowledge the micro-fabrication facilities and the staff at Purdue University for their assistance. We would also like to thank Indiana 21st Century Research and Technology fund for undergraduate research support for Ms. Vandna Handa and Mr. Eric Tkaczyk.

Author information



Corresponding author

Correspondence to Rashid Bashir.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Tkaczyk, E., Handa, V., Lee, S. et al. Determination of the Charge Attached to Micro-scale Devices Used in Fluidic Self-Assembly Processes. MRS Online Proceedings Library 737, 853 (2002).

Download citation