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

Published online by Cambridge University Press:  11 February 2011

Eric Tkaczyk ,
Vandna Handa ,
Sangwoo Lee ,
Helen McNally ,
Lichuan Gui ,
Steve Wereley  and
Rashid Bashir
Eric Tkaczyk
Affiliation:
School of Electrical and Computer Engineering
Vandna Handa
Affiliation:
School of Electrical and Computer Engineering
Sangwoo Lee
Affiliation:
School of Electrical and Computer Engineering
Helen McNally
Affiliation:
School of Electrical and Computer Engineering
Lichuan Gui
Affiliation:
School of Mechanical Engineering, Purdue University, W. Lafayette, IN 47907
Steve Wereley
Affiliation:
School of Mechanical Engineering, Purdue University, W. Lafayette, IN 47907
Rashid Bashir
Affiliation:
School of Electrical and Computer Engineering Department of Biomedical Engineering [email protected]
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Abstract

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.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 737 , 2002 , F8.53
Copyright
Copyright © Materials Research Society 2003

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References

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