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Indirect electro-osmotic pumping


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Guijt, RM, Lichtenberg, J, de Rooij, NIF, Verpoorte, E, Baltussen, E and van Dedem, GWK 2002 , 'Indirect electro-osmotic pumping' , Journal of the Association for Laboratory Automation, vol. 7, no. 3 , pp. 62-64 , doi: 10.1016/S1535-5535(04)00195-9.

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The manipulation of liquids within a microcapillary network
remains a considerable challenge in the development
of miniaturized total chemical analysis systems
(μTAS). Fluid manipulation can be achieved using (micro)
mechanical pumps connected or integrated into the device, and by
using an electric field (E) for generation of electro-osmotic flow
(EOF). For glass microdevices, electro-osmotic pumping (EOP) is
most attractive, since no moving parts and/or valves are required.
In its simplest embodiment, EOP in microfluidic devices
involves imposing an E along the full length of the channel by
immersing electrodes into open solution reservoirs situated at both
ends of the channel. Electrolytically generated gases at the electrodes
drift to the surface of the solution reservoirs and escape into the air.
In more complex situations, however, EOP in a subsection of a
microchannel may be required. For sampling, for example, from
brain tissue in living organisms, the presence of electrodes in the
‘sample reservoir’ (i.e., the brain), and thus outside the microdevice
is undesirable, since potentials applied to external electrodes interfere
with the sampling environment. In these cases, electrodes need
to be integrated into the microfluidic device. The use of electrodes
in a microchannel, however, is not trivial. Electrolytic gases get
caught in the sealed microchannel and hence effectively interrupt
the electric field, and thus fluid movement. A number of
approaches to avoid bubble formation during spatially localized
application of voltages in microfluidic networks have been
reported. In one example, a 1-mm-thick poly(dimethylsiloxane)
(PDMS) substrate containing the microchannel was sealed with a
glass cover plate containing the electrodes.1 Electrolytic gases
formed at the electrodes dissipated through the highly gas-permeable
PDMS film into the air.
An alternative method for application of the electric field is the
use of a conducting barrier between the electrodes and the channel.
A Nafion membrane has been presented as an interface
between an open reservoir containing the electrode and a
microchannel.2 Electrolytic gases dissipate into the air via the open
reservoir, while the electrical contact afforded by the membrane
ensured that an E was applied to the closed microchannel. A similar
approach involves the use of adjacent side channels, which are
electrically connected, via porous barriers, but where fluid
exchange is strongly limited.3,4 Either the porous membrane was
formed using a thin layer of potassium silicate, in or the contact
was directly over the glass wall separating adjacent channels.
The three approaches mentioned above allow the creation of
field-free zones in addition to regions where the field is applied. In
the field-free regions, charge-independent fluid transport can be
controlled by EOP elsewhere in the microfluidic system, an effect
we term “electro-osmotic indirect pumping” (EOIP) to distinguish
between EOP in- and outside the electric field.
In this paper, a glass microdevice for both EOP and EOIP using
electrically connected side channels is presented. Electrical contact
between the main and side channels is achieved by electrical breakdown
of the glass barrier between these channels. Electrical breakdown
for initiating liquid contact between disconnected channels
has been demonstrated in PDMS devices.5 To our knowledge, this
is the first time that electrical breakdown for initiation of electrical
contact between glass microchannels is presented. Cross injection
by a combination of EOP and EOIP is demonstrated.

Item Type: Article
Authors/Creators:Guijt, RM and Lichtenberg, J and de Rooij, NIF and Verpoorte, E and Baltussen, E and van Dedem, GWK
Keywords: electro-osmotic pumping, sampling, miniaturized total analysis system, fluid manipulation
Journal or Publication Title: Journal of the Association for Laboratory Automation
ISSN: 1535-5535
DOI / ID Number: 10.1016/S1535-5535(04)00195-9
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