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Electro-osmotic
Pumping
(by Dr. Paul V.
Rainey) |
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The
development of MEMS techniques has permitted the fabrication
of microfluidic devices for chemical analysis including pumps,
valves, flow sensors, separation capillaries, and chemical
detectors. The advantages of miniaturized chemical analysis
systems, increased speed, reduced reagent cost, reduced waste
and in-situ analysis, have been predicted to revolutionize
chemistry in the same way that the invention of the PC paved
the way for the information revolution. In particular,
interest in miniaturized Capillary Electrophoresis devices has
grown dramatically, the advantages being the analysis of many
different species at once and valveless flow removing the need
for moving parts, which have proven difficult to down
scale.
Fluid
pumping in capillary electrophoresis is achieved by a
phenomena known as Electro-osmotic flow (EOF). EOF is fluid
motion induced by the interaction between the fluid charge at
the wall of the channel and the external applied electric
field. The rate of flow is proportional to applied voltage, pH
and conductivity of the solution, and material of channel
wall. It’s primary advantage over other pumping schemes is the
fact that valves are not required to control fluid flow; the
voltage magnitude and polarity are used to do
this.
Click here to view a
video clip of liquid being electrically 'pumped' along a
100µm wide channel fabricated in the surface of
silicon. |
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Figure 1. Electro-osmotic pumping test
structure. |
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References
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Rainey PV, Mitchell SJN, and
Gamble HS, “Optimization of conductivity monitoring in
micromachined silicon capillaries”,
SPIE Journal of Microlithography, Microfabrication, and
Microsystems, vol. 1, issue 2, pp159-165 July 2002.
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Rainey PV, Mitchell SJN
and Gamble HS,
“SPICE modelling of liquid capacitance in
micromachined silicon capillaries”,.
Proc. SPIE : MEMS Design,
Fabrication, Characterisation and Packaging, vol. 4407, pp61-67,
Edinburgh, May 2001.
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Rainey PV, Mitchell SJN, Gamble HS,
“Electro-Kinetic Pumping In Silicon Based Capillaries” EPSRC
PREP 2001, Keele UK, April 2001.
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