INTEGRATED MICROFLUIDIC CAPILLARY

ELECTROPHORESIS SYSTEM FOR BIOCHEMICAL

ANALYSIS ON MARS AS PART OF THE UREY

INSTRUMENT Peter A. Willis

1, J. Anthony Smith

1, Frank Greer

1,

Frank J. Grunthaner1, Larry Epp

1, Dan Hoppe

1, Thomas N. Chiesl

2,

Richard A. Mathies2, Jacob J. Sprague

3, and Jason P. Rolland

3

1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA,

USA 91109 2University of California, Berkeley, CA, USA 94720

3Liquidia Technologies Inc., Research Triangle Park, NC, USA 27709

ABSTRACT

The Urey Instrument [1] contains at its core a microfluidic capillary electropho-

resis (μCE) system [2] utilizing on-chip perfluoropolyether (PFPE) membrane

valves and pumps [3]. This instrument entered into Phase A of flight development at

JPL in April 2008, and is scheduled for completion in November 2011. Recent pro-

gress in this endeavor and current efforts at JPL are discussed.

KEYWORDS: capillary electrophoresis, diaphragm valve, planetary exploration

INTRODUCTION

The ultimate goal of the μCE subsystem of the Urey Instrument is to perform ul-

trasensitive compositional and chiral analysis of amino acids in order to determine if

Mars harbors biochemical signatures of past or present life. Samples assayed by the

CE susbsystem come in the form of sublimed films of extracts from the Martian re-

golith provided by a secondary instrument subsystem. This instrument is scheduled

to explore the Martian surface as part of the Pasteur Payload of the 2013 ExoMars

astrobiology mission.

The current state-of-the-

art lab-on-a-chip prototype

is a four-layer wafer stack

design first described by

Skelley [2]. This design

utilizes μCE channels

patterned in glass, along

with a flexible membrane, a

pneumatic manifold layer,

and a fluidic bus layer. A

photograph of a four-layer

device of this type fabri-

cated with a PFPE

membrane is shown in

Figure 1. Figure 1. Photomicrograph of a 4-layer μCE device

978-0-9798064-1-4/µTAS2008/$20©2008CBMS 408

Twelfth International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 12 - 16, 2008, San Diego, California, USA

Three pneumatically driven on-chip diaphragm valves placed in series are used to

peristaltically pump reagents, buffers, and samples to and from capillary electropho-

resis electrode wells. Electrophoretic separation occurs in the all-glass channels near

the base of the structure.

RESULTS AND DISCUSSION

The first and most

pressing effort in the flight

development process

following the demonstration

of basic instrument function

[2] was to select and begin

qualification of a flight-

robust membrane used in

hardware intended for

exploration of Mars. To this

end, in late 2007 and early

2008, a comprehensive

protocol of long-term valve

testing was performed in

order to determine the

choice of material used for

the flight instrument

membrane. The performance of three different membranes: PFPE, PDMS, and Tef-

lon were monitored throughout a programmed sequence of extended physical and

thermal stress-testing. Individual valves were actuated hundreds of thousands of

times and temperature cycled between +50°C and -50°C thirty times, to simulate the

experience of in situ operation. Devices were periodically characterized to deter-

mine if the valve sealing characteristics had changed. In this analysis, both PFPE

and PDMS devices were found to be essentially unaltered by the process (See Figure

2). However it was possible to witness changes in Teflon devices after extreme

combinations of temperature cycling and actuation. In some devices, valves were

found to become more tightly sealed, significantly hindering the pumping rate of de-

vices fabricated from Teflon devices. Another salient observation made during this

time frame was that PDMS devices left unused for extended periods became sealed

permanently shut, presumably due to dehydration at the PDMS/glass interface. For

these reasons, PFPE was chosen as the primary option for flight development, with

PDMS taken as the backup option (requiring a solution to the long term sealing

problem, which is not witnessed with PFPE devices). Current work involves electri-

cal characterization of integrated devices.

A second active area of investigation during the early Phase A work involves

simulation of device function, utilizing a more complex integrated six-channel sys-

tem with additional functionality. A 3D SolidWorks model of a more highly inte-

grated ‘flight-like’ six-channel autonomous system is shown in Figure 3. This vir-

tual system includes a manifold coupling interface which performs two critical

functions: it houses all miniature solenoid valves (144 in total) required for opera-

Figure 2. Pumping characteristics of a PFPE device

before and after one million actuations and 30 tem-

perature cycles. Note device is essentially unchanged.

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Twelfth International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 12 - 16, 2008, San Diego, California, USA

tion of six independent μCE stack sys-

tems, as well as housing hollowed-out

compartments for reagent and waste

storage. Custom-written code written

in Comsol multiphysics software is

used to model both the electric fields

present and their effects upon electro-

phoresis and plug generation (Figure

4). Both time independent (electric

field strength) and time dependent

(electrokinetic injection and separa-

tion) phenomena are simulated using

the model system. This modeling is

used to inform the layout and design

of the power supply system under par-

allel development.

ACKNOWLEDGEMENTS

The research described in this paper was carried out at the Jet Propulsion Labora-

tory, California Institute of Technology, under a contract with the National Aeronau-

tics and Space Administration.

REFERENCES

[1] A.D. Aubrey et al., Astrobiology, 8(3), in press, (2008).

[2] A.M. Skelley et al., Proc. Natl. Acad. Sci. U.S.A., 102, pp. 1041-1046 (2005).

[3] P.A. Willis et al., Lab Chip, DOI: 10.1039/b804265a (2008).

Figure 3. SolidWorks model of six-channel

virtual μCE instrument

Figure 4. Comsol Multiphysics Modeling of static electric fields (right) and electroki-

netic injection (left) in six-channel virtual μCE instrument

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Twelfth International Conference on Miniaturized Systems for Chemistry and Life SciencesOctober 12 - 16, 2008, San Diego, California, USA