by
Bruce Kent Gale
A dissertation submitted to the faculty of
The
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy
Department of Bioengineering
May 2000
Copyright © Bruce Kent Gale 2000
All Rights Reserved
SUPERVISORY COMMITTEE APPROVAL FORM
FINAL READING APPROVAL FORM
In this work the complete motivation, design, fabrication, and characterization of a microscale electrical field- flow fractionation (ElFFF) system is presented. The general theory for field flow- fractionation (FFF) systems is reviewed and demonstrates that miniaturization, while providing some advantages, does not purport to improve the capabilities of FFF systems. A closer look, specifically at the ElFFF system, though, indicates the numerous potential advantages for miniaturizing ElFFF systems. The advantages from miniaturization are explored thoroughly and a determination is made that a microscale ElFFF system could provide numerous benefits such as improved resolution and reduced analysis times, as well other advantages. The components involved in ElFFF systems are then reviewed and a design for a microscale ElFFF system is developed. The fabrication for a m-ElFFF system is outlined and the micromachining processes used in fabrication described. A completed m-ElFFF system is demonstrated and characterized with regard to most of the important parameters regarding ElFFF systems. These parameters include plate heights, resolution, equilibration times, electrode time constants, and effective electric fields, as well as several other parameters. The capabilities of the fabricated system are demonstrated by retaining and separating polymer particles by both size and surface charge, polymer particles with attached proteins, and by retaining and separating whole blood. Thus, the microscale system is shown to function in accordance with theory, and to meet the expectations developed before the system was fabricated.
In addition to the m-ElFFF system, the design and fabrication of a microscale electrical impedance detector is presented. The detector is characterized with regard to its detection abilities using three different modes of operation. Each of these modes, either DC, AC, or impedance spectroscopy, has their own unique advantages and disadvantages, but each is clearly able to detect the type of particles currently of interest for analysis in ElFFF systems. The detector is shown to improve the operation of the m-ElFFF by reducing plate heights in the complete system. The detector in electrical impedance spectroscopy mode also demonstrates the potential for making particle size measurements, further increasing the analytical capabilities of the complete m-ElFFF system.
TABLE OF CONTENTS
ABSTRACT......................................................................................................................... iv
LIST OF SYMBOLS........................................................................................................... viii
ACKNOWLEDGMENTS...................................................................................................... x
Chapter
1 INTRODUCTION..................................................................................................... 1
Scope of Work...................................................................................................... 1
Bioinstrumentation................................................................................................. 2
Electrical Field- Flow Fractionation......................................................................... 5
Micromachining..................................................................................................... 8
Biochemical Analysis System Detectors................................................................ 11
Chapter Outlines.................................................................................................. 16
2 THEORY AND SCALING EFFECTS...................................................................... 17
Introduction......................................................................................................... 17
General FFF Theory............................................................................................. 20
ElFFF Theory...................................................................................................... 37
Scaling Effects..................................................................................................... 52
Conclusion........................................................................................................... 70
3 m-ElFFF SYSTEM DESIGN AND FABRICATION.................................................. 72
Introduction to Microfabrication............................................................................ 72
ElFFF System Components................................................................................... 81
m-ElFFF System Parameters and Design............................................................... 84
m-ElFFF Channel Fabrication............................................................................... 104
Packaging.......................................................................................................... 110
Fabrication Results............................................................................................. 115
Preliminary Biocompatibility Testing.................................................................... 122
Conclusion......................................................................................................... 126
4 m-ElFFF SYSTEM CHARACTERIZATION.......................................................... 127
Introduction........................................................................................................ 127
Methods............................................................................................................ 128
Results and Discussion....................................................................................... 132
Conclusion......................................................................................................... 173
5 IMPEDANCE DETECTOR CHARACTERIZATION............................................ 176
Introduction........................................................................................................ 176
Theory............................................................................................................... 179
Fabrication......................................................................................................... 185
DC Mode Operation........................................................................................... 185
AC Mode and Impedance Spectroscopy.............................................................. 198
Conclusions........................................................................................................ 213
6 BIOLOGICAL ANALYSIS................................................................................... 219
Introduction........................................................................................................ 220
Methods............................................................................................................ 222
Results.............................................................................................................. 223
Conclusion......................................................................................................... 228
7 CONCLUSION..................................................................................................... 230
Macro and Micro Systems Compared.................................................................. 231
Future Work and Limitations of this Study............................................................ 233
Appendices
A NUMERICAL SOLUTIONS FOR STOKES FLOW............................................... 244
B WATER DYNAMICS IN VERY LOW ASPECT RATIO CHANNELS................. 258
REFERENCES.................................................................................................................. 274
a.................................................................................................................................... radius
b...................................................................................................................... channel breadth
c.......................................................................................................................... concentration
c0................................................................................................................ initial concentration
d................................................................................................................................ diameter
di......................................................................................................... steric
inversion diameter
e....................................................................................................................... electron charge
f.......................................................................................... friction coefficient or friction factor
gx.............................................................................................................. gravity in x-direction
h................................................................................................... gridline spacing in x-direction
i.................................................................................................................................... current
i.................................................................................................... gridline number in x-direction
j................................................................................................... gridline number in y-direction
k.............................................................................................................. Boltzmann’s constant
k................................................................................................... gridline spacing in y-direction
l................................................................................................. induced sample layer thickness
m............................................................................................. number of gridlines in x-direction
n............................................................................................. number of gridlines in y-direction
ni0........................................................ initial number of active ions per volume (number density)
p................................................................................................................................. pressure
s............................................................................................................................ scale factor
t........................................................................................................................................ time
tm.............................................................................................................. membrane thickness
tr......................................................................................................................... retention time
t0................................................................................................................................ void time
u, ux................................................................................................. flow velocity in x-direction
v.................................................................................................................................. velocity
vy...................................................................................................... flow velocity in y-direction
ávń........................................................................................................... average flow velocity
ávńzone...................................................................... average flow velocity for a zone of particles
w......................................................................................................... plate separation distance
wz..................................................................................................... flow velocity in z-direction
w1/2..................................................................................................... peak width at half height
x................................................................................................................. coordinate direction
xDL.......................................................................................................... double layer thickness
y................................................................................................................. coordinate
direction
z.................................................................................................................................... charge
z................................................................................................................. coordinate direction
A.......................................................................................... distance from origin to peak elution
C........................................................................................................................... capacitance
CB................................................................................................................... bulk capacitance
CDL.................................................................................................... double layer capacitance
Cp............................................................................................................ specific heat capacity
D............................................................................................................... diffusion coefficient
Dh................................................................................................................ hydraulic diameter
E.............................................................................................................. electric field strength
Eeff.............................................................................................. effective electric field strength
Ey.................................................................................................................. Young’s modulus
H............................................................................................................................ plate height
HD....................................................................................... diffusion contribution to plate height
Hi.................................................................................. instrumental contribution to plate height
Hn............................................................................... nonequilibrium
contribution to plate height
Hp..................................................................... sample
polydispersity contribution to plate height
JD............................................................................................................... flux due to diffusion
JF.................................................................................................... flux due to the applied field
K....................................................................................................................................... gain
L........................................................................................................................ channel length
Le...................................................................................................................... entrance length
N.................................................................................................................... number of plates
P.................................................................................................................................... power
Q...................................................................................................................... thermal energy
Q.................................................................................................................... volume flow rate
R......................................................................................................................... retention ratio
.............................................................................................. average
value of retention ratio
RB....................................................................................................... bulk electrical resistance
Re............................................................................................................... electrical resistance
Re................................................................................................................ Reynolds’ number
Rh................................................................................................... hydraulic Reynolds’ number
Rs.............................................................................................................................. resolution
S’.............................................................................................................. applied field strength
Sd.............................................................................................................. size selectivity index
T........................................................................................................................... temperature
U.......................................................................................................................... drift velocity
Ve....................................................................................................................... elution volume
V0.......................................................................................................................... void volume
V.................................................................................................................................. voltage
Veff.................................................................................................................. effective voltage
Z............................................................................................................................. impedance
ZT..................................................................................................................... total impedance
a............................................................................................................................ aspect ratio
b................................................................................................. membrane deflection constant
g.............................................................................................................. steric transition factor
e............................................................................................................................. permittivity
eDL............................................................................................................................. permittivity
of the double layer
er...................................................................................................................................................... relative permittivity
e0....................................................................................................... permittivity of free space
f................................................................................................................... field susceptibility
z.......................................................................................................................... zeta-potential
h................................................................................................................................ viscosity
h0....................................................................................................................... initial viscosity
k.......................................................................................................................... Debye length
l......................................................................................... nondimensional retention parameter
m........................................................................................................... electrophoretic mobility
rB........................................................................................................ bulk electrical resistivity
re................................................................................................................ electrical resistivity
rm................................................................................................................................. density
s.................................................................................................................. standard deviation
....................................................................... average
standard deviation along the time axis
t.......................................................................................................................... time constant
There are a number of
organizations and individuals that I would like to thank for their help on this
project. I could not have completed this
work without their support.
Specifically, I would like to acknowledge financial support from a
National Science Foundation graduate research fellowship, a Whitaker Foundation
internship, and a University of Utah Technology Innovation Grant. Amoco Chemical Corporation and Microchem
Corporation both graciously donated items to further this work. Many thanks are in order for the staff at
HEDCO Microelectronics Laboratory. Their
long hours and dedicated service kept the research on track. I would also like to thank the secretaries
and staff in the Bioengineering Department office for their constant
willingness to help and their ability to get things done quickly.
I would especially like to thank all the members of the Micro Instrumentation Research Lab for their constant support, good ideas, and restful entertainment. I would specifically like to thank Thayne Edwards for his help with the finite element modeling, Ian Papautsky for his help with the microfluid flow studies, and Jeff England for his help with the data acquisition system.
I would like to express appreciation to my supervisory committee for their insight, suggestions, and constant dose of reality. Thanks to Tim Ameel for a listening ear and a profound interest in the people around him. Thanks to Karin Caldwell for being the example of a world-class scholar, an enthusiastic researcher, an able administrator, and a caring person. I would especially like to thank my advisor Bruno Frazier for his bright vision of the future, his willingness to take on a confused student, and his desire to make any situation beneficial to all involved. It wasn’t an accident that we arrived and departed together.
Most importantly, I would like to thank my wife Chela for her constant support, patience, and forgiveness, without which none of this work would have been possible. I would also like to thank my parents for instilling and encouraging a desire to learn and for teaching the value of work. Many thanks to my brother Adam whose competitive nature (and mine) brought out the best in both of us. Lastly, I would like to thank God for blessing me with a multitude of abilities and opportunities.
Collecting biological samples for diagnosis or other analysis, sending them off to a lab, and then waiting for hours, days, or even weeks for results is a typical scenario for doctors, patients, and other scientists in health care, chemical analysis, environmental monitoring and other fields. Typically, medical and chemical analyses must be performed in dedicated labs because the analysis systems are bulky, slow, expensive, delicate, and often complex. There is a great demand for speeding up these analysis systems and moving them to the location where the results are needed. A h