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IEEE JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 8, NO. 1, MARCH 1999
Electric Impedance Spectroscopy Using
Microchannels with Integrated Metal Electrodes
H. Edward Ayliffe, A. Bruno Frazier, Member, IEEE, and R. D. Rabbitt
Abstract—Microelectric impedance measurement systems containing microchannels with integrated gold electrodes were fabricated to enable EI measurements of femtoliter (10015 ) volumes
of liquid or gas. The microinstruments were characterized using
samples of air, partially deionized water, and saline solutions with
various ionic concentrations over the frequency range of 100 Hz
to 2 MHz. Resulting spectral patterns varied systemically as a
function of ionic concentration. In addition to industrial sensing
applications, this technology may prove to be beneficial in monitoring microsystems utilizing on-chip fluid chemistry, measuring
the dielectric dispersion of polymer solutions, and determining
the electrical properties of isolated biological materials. [296]
Index Terms— Biological cells, electric impedance, micromachine, spectroscopy.
I. INTRODUCTION
E
LECTRIC impedance (EI) measured in a onedimensional (1-D) electric field is an established
method for interrogating the electromagnetic behavior of
isolated materials and composite systems. Microfabrication
techniques offer a low-power means of applying traditional
EI concepts to the investigation of complex-valued dielectric
properties of small structures and material samples. Reducing
the overall size of an EI measurement device allows for
increased spatial resolution while limiting the possibility
of dielectric breakdown by minimizing the strength of the
required electromagnetic field. In addition, microscale EI
devices can be fabricated to interrogate femtoliter subdomains
within nanoliters of total sample solution.
In previous works, microfabricated EI sensors have demonstrated the ability to sense variations in solution temperatures, ionic concentrations, hydrogen peroxide concentrations,
and even antigen-antibody binding (immunosensors) [1], [2].
These systems typically interrogate solutions using an array
of surface-mounted metal electrodes with an active surface
area of 1 mm . To further reduce the required sample size,
we fabricated EI systems containing microchannels lined with
metal electrodes. The devices allow materials to be positioned
between interrogating electrodes using rapid and efficient
fluid transport methods [3]–[5]. In addition to the numerous
Manuscript received August 22, 1997; revised September 14, 1998. This
work was supported in part by the Whitaker Foundation and the University
of Utah. Subject Editor, K. Petersen.
H. E. Ayliffe and R. D. Rabbitt are with the Department of Bioengineering, University of Utah, Salt Lake City, UT 84112-9202 USA (e-mail:
ted.ayliffe@m.cc.utah.edu).
A. B. Frazier is with the Department of Electrical Engineering, University
of Utah, Salt Lake City, UT 84112-9202 USA.
Publisher Item Identifier S 1057-7157(99)01184-1.
applications microscale EI devices have in basic science and
engineering, their size makes them especially suitable for
biological studies.
An investigation into the dielectric properties of proteins is
one of many possible applications for an integrated microchannel/EI measurement system. The electrical characteristics of
protein solutions are believed to play an important role in
physiologic functions that involve protein–protein and charged
ligand interactions [6]–[8]. In these studies, the dielectric
dispersions of protein solutions were described in terms of
the summation of distributed charges within the protein (polarization vector) and proton fluctuations.
Microscale EI devices can also be applied to measure the
dielectric properties of individual cells and cell aggregates.
Cellular electrical properties are typically expressed as voltage/chemically dependent membrane capacitance, membrane
resistance, and cytoplasmic resistance—properties which are
critical to the physiology of all living cells. The three most
common techniques that have previously been applied to measure cellular electrical properties include the EI cell suspension
technique [9]–[11], whole-cell patch clamping [12]–[14], and
electrophoresis/electrorotation [15]–[26]. All of these methods
rely on estimates of cell geometry for the accurate calculation
of the electrical parameters and are generally limited to wholecell resolution. Microchannels outfitted with EI measurement
electrodes have the potential to supplement these traditional
methods by providing increased spatial resolution (by using
electrodes smaller than a single cell and by constraining the
cell within the microchannel) and extending the frequency
range [27].
This paper describes the fabrication of a device suitable
for EI measurements of femtoliters of fluids, solutions, suspended particles, and single cells. Fig. 1 is a schematic of the
microdevice in which two fluid reservoirs are connected by
a single microchannel that narrows to a width of 10 m
in the recording zone (channels are 4 m high). The microchannels were constructed from epoxy-based photoresist on
quartz glass wafers. Full-depth gold measurement electrodes
were integrated into the narrowest portion of the microchannels. Through holes were wet etched in glass coverslips and
bonded to the microstructures to form the top surface of the
microchannels. The resulting microchannels and electrodes
are sandwiched between planar glass substrates exhibiting
excellent optical qualities and allowing for direct sample
observation using transmission light microscopy. Parasitic
capacitance between the electrodes is minimized by isolating
the electrodes on all sides with materials with high dielectric
1057–7157/99$10.00  1999 IEEE
AYLIFFE et al.: ELECTRIC IMPEDANCE SPECTROSCOPY USING MICROCHANNELS
51
Fig. 1. Schematic of microelectric impedance measurement device with gold
electrodes integrated into a microchannel.
constants (glass and epoxy-based photoresist). The microEI measurement system was characterized using biological
concentrations of ionic salt solutions, air, and deionized (DI)
water over the frequency range of 100 Hz to 2 MHz. In
addition, preliminary EI data from human polymorphoneuclear
leukocytes (PMN’s) and teleost fish red blood cells (RBC’s)
positioned within the recording zone demonstrate the potential
to use EI spectral patterns to distinguish cell types.
II. METHODS
A metal seed layer (250 Å Ti and 750 Å Au) was sputtered on 3-in-diameter quartz glass (Pyrex 7740) substrates,
patterned, and etched to form the approximate electrode dimensions, electrical connecting pads, and the conducting grid
for electroplating [Fig. 2(1)]. A 4.5- m-thick layer of epoxybased photoresist SU-8 (Microlithography Chemical Corp.,
Newton, MA) was spun over the metal seed layer and patterned
to form the fluid reservoirs and the wider portions of the
connecting channel [Fig. 2(2)]. Gold microelectrodes were
slowly electroplated using a low-current density (1 mA/cm )
until the electrodes were 0.5 m below the top surface
of the photoresist [Fig. 2(3)]. Following electroplating, the
photoresist was cured on a hot plate at 125 C for 15 min
to reduce cracking during subsequent fabrication procedures.
A 6000-Å-thick layer of aluminum was then sputtered on
the entire wafer, patterned, and etched to act as a mask for
the microchannel etching procedure [Fig. 2(4)]. An oxygen
plasma etch was used to form the narrowest portion of
the microchannel ( 10 m wide), which lies between the
gold electrodes [Fig. 2(5)]. The unwanted photoresist and
aluminum were then wet etched from the surface of the wafer
and thoroughly rinsed in DI water in preparation for coverslip
bonding [Fig. 2(6)].
Coverslips were fabricated to enclose the microchannels by
providing the top surface of the channels and simultaneously
add depth to the fluid reservoirs. Baxter Scientific no. 1.5
Fig. 2. Micromachining steps for fabrication of a microelectric impedance
device. Fabrication of microelectric impedance device. (1) Sputter and pattern
metal (Ti and Au) electroplating seed layer. (2) Spin on SU-8 photoresist and
pattern for electroplating and fluid reservoirs. (3) Electroplate gold electrodes.
(4) Sputter and pattern Al mask layer for microchannel etching. (5) O2 plasma
etch microchannels and remove Al layer. (6) Bond glass coverslips.
coverslips (McGaw Park, IL) were sputtered on both sides
with a layer of chromium and gold. The metal layers were
patterned and etched to expose clean glass in the areas forming
the reservoirs and a border to separate each coverslip from
neighboring glass. Additional photoresist was spun on and
patterned on both sides to act as an additional mask during
the glass etching. The exposed glass areas were wet etched
in a 50% HF acid and DI water solution at 30 C. The
square reservoir holes were etched completely through the
200- m-thick coverslips after approximately 15 min in the
acid etchant. Once the individual coverslips were formed, the
masking materials (Cr, Au, and photoresist) were stripped, and
the coverslips were cleaned using a 70 : 30 solution of H SO
and H O in preparation for bonding.
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IEEE JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 8, NO. 1, MARCH 1999
The fabricated coverslips were aligned over selected microchannel/electrode structures using a micromanipulator and
an inverted light microscope (Olympus IMT2, Lake Success,
NY). Once in position, pressure was applied to the center of the
coverslip to prevent slippage and reduce the air gap between
the glass and underlying microstructures. Small ( 0.5 l)
drops of UV curable PVC adhesive (Loctite 3301, Rocky Hill,
CT) were applied to the coverslip edge and allowed to wick
under the glass by capillary forces. The compressive load from
the micromanipulator slowed the flow of adhesive and greatly
delayed the adhesive from flowing into the microchannels. The
adhesive flow was monitored by light microscopy and was
cured in place by switching on an ADAC Technologies UV
source (Bantan, CT).
Glass pipettes were bonded over the coverslip holes both
to provide a simple and reliable means for connecting the
microchannels to the external reservoirs and to help prevent
unwanted evaporation of the small aliquots of test samples.
The ends of 2-mm-square glass tubing (Friedrick and Dimmock, Millville, NJ) were cut at approximately 45 and ground
smooth using a hand-held rotary tool (Craftsman, Sears Roebuck Co, Chicago, IL) to a length of 10 mm. The glass tubes
were aligned and held in place over the fluid reservoirs using
a micromanipulator and an Olympus dissecting microscope.
The same UV curable bonding technique used to bond the
coverslips was used to adhere the pipettes to the coverslips.
Following bonding, the devices were tested for leaks using
DI water under light microscopic observation. With the glass
tubes in place, soft Silastic tubing (Dow Corning, Midland,
MI) could be connected to the glass tubes to manipulate bulk
flow with the application of positive or negative pressure.
Six devices were electrically characterized over a frequency
range of 100 Hz to 2 MHz using varying concentrations of
phosphate buffered saline (PBS) solutions (0.5, 1, 5, and 10
times the physiologic concentration of 300 mOsm), DI water,
and air. The gold electrodes were connected to a computercoupled (IEEE 488, GPIB) impedance analyzer (HP4194A)
using a minimal length ( 18 in) of 22-gauge RF lead wire
(Channel Master, Smithfield, NC) outfitted with gold tips. Prior
to performing the impedance measurements on each device,
the impedance analyzer with the cable connected was set to the
open circuit configuration. The gold-tipped cable was brought
into contact with the bonding pads on the microdevice using
micromanipulators. Three consecutive impedance sweeps were
recorded on the empty device (air measurements). DI water
was added to the open fluid reservoir and negative pressure
was applied to the opposite reservoir via flexible tubing to help
the water flow completely into the microchannel. To assure that
the fluid had filled the channel, it was continuously monitored
with a Nikon Diaphot 200 confocal microscope (Melville,
NY). After the DI water filled the channel, three consecutive
impedance sweeps were performed. The four PBS solutions
were measured from low to high salt concentration using the
same method. Between each PBS solution measurement, water
was flushed through the device for approximately 5 min using
negative pressure and allowed to air dry.
PMN’s and RBC’s were selected for the initial wholecell studies using the micro-EI devices. The PMN’s were
obtained from healthy human donors and supplied by the
Cardiovascular Research and Training Institute (CVRTI) at the
University of Utah. Blood was stored at 4 C for no longer than
8 h. Leukocytes were isolated following methods previously
reported by Keller et al. (1983) [28]. The RBC’s were obtained from a teleost fish, Opsanus tau. Unlike mammalian
erythrocytes, these RBC’s are nucleated, have dimensions
similar to human PMN’s, and hence are appropriate for EI
spectral comparison. An aliquot of cell suspension was then
added to the cell reservoir of the microdevice. The temperature
of the device and cells was maintained at 19 C. Microbore
silicone tubing was secured to the fluid reservoir opposite the
cells to control the channel flow using suction. Cell-loaded
devices were positioned on the stage of an inverted Nikon
confocal microscope. The RF lead wires, configured with
rigid gold contacts, were lowered under visual observation to
mate with the gold contact pads on the surface of the device.
The network analyzer was appropriately calibrated to account
for RF transmission to the remote recording site. Cells were
positioned between the electrodes via control of the bulk flow
with pressure. EI spectra were measured between electrode
contact pads over the frequency range from 100 Hz to 2
MHz. For each cell, the EI spectra were recorded with bathing
solution in the recording zone and with a stationary cell in the
recording zone. Raw spectral data, collected in this way, are
therefore sensitive to dielectric properties of the microdevice,
the material sample, and the geometrical configuration.
III. RESULTS
A scanning electron micrograph (SEM) of one of the
microchannels with the integrated gold electrodes is shown
prior to coverslip bonding in Fig. 3. The microchannel in
the figure measures 10 m wide and 4.3 m deep with
the gold electrodes measuring 8.0 m wide and 4.0 m
thick. The microchannel width was designed slightly wider
than the electrode gap to ensure solution/electrode contact.
For this reason, the gold electrodes typically extended into
the channel 1–2 m on each side. The resulting average
distance between the tips of the electrodes, or electrode gap,
measured 7.1 m. Prior to coverslip bonding, the depth of
the channels was measured using a Dektak IIA profilometer
(Sloan Technologies, Santa Barbara, CA) and found to vary by
only 0.11 m with a mean value of 4.31 m. Devices with a
total of eight different microchannel and electrode geometries
were designed and fabricated on each wafer. An SEM of a
microchannel with a bonded coverslip is shown overlaid on
an image of an electrode/microchannel device prior to bonding
(see Fig. 4). Square holes were wet etched completely through
the 200- m-thick coverslip glass in addition to etching each
coverslip free from the adjacent neighbors. The gold bonding
pads are shown in Fig. 4 extending from the edges of the
bonded glass coverslip.
Fig. 5 shows the magnitude and phase of the EI of one
device as a function of frequency when filled with air and
the five different solutions between the electrodes. Individual
curves are averages of three frequency sweeps. Resolution
was limited to magnitudes 100 M . For this reason, the
AYLIFFE et al.: ELECTRIC IMPEDANCE SPECTROSCOPY USING MICROCHANNELS
53
Fig. 3. SEM of microchannels with integrated gold electrodes prior to coverslip bonding.
Fig. 4. SEM of a coverslip bonded to a microstructure can be seen (right) overlaid on an SEM of an electrode/microchannel device prior to bonding.
impedance of the air-filled device could not be measured at
frequencies below 100 kHz. Resulting EI data reflect properties
of both the material sample in the microchannel and the
current path around the sample (i.e., dielectric properties
of the microdevice). Differences between the magnitude of
the impedance for the five salt solutions were statistically
tested at 10, 100, 500 k,
significant (student -test,
and 1 MHz). The average magnitude of impedance for the
solutions demonstrated a nearly linear response with a constant
slope (on a log scale) over the frequency range of 1 kHz to
2 MHz. Larger magnitudes correspond to the solutions having
lower ionic concentrations. The phase angle generally becomes
flatter for solutions with lower ionic concentrations (lower
conductivity).
Variations between devices were also examined. Eight different EI devices were designed and six were tested. Due
to fluctuations in the design and fabrication process, the
resulting microstructures have varying microchannel widths,
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IEEE JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 8, NO. 1, MARCH 1999
Fig. 5. (a) Magnitude and (b) phase of the device impedance with air, DI
water, and varying concentrations of PBS between the electrodes.
electrode shapes, and electrode gaps. This variability requires
that each device be calibrated using materials of known
dielectric properties for applications requiring measurement of
the absolute constitutive properties of the sample. Fig. 6 shows
the magnitude and phase of impedance versus frequency of
six devices filled for the 300 mOsm concentration of PBS. All
of the devices tested using this solution displayed impedance
curves with similar characteristics. Although the magnitude
of the impedance can be seen to decrease with increasing
frequency for all of the devices, the rate of decrease and
starting magnitude varied by up to one order of magnitude.
In addition, the corresponding phase angles were considerably
different between devices. Differences are believed to be due
to variability in channel/electrode dimensions and geometry
(see Table I).
The presence of biological cells between the electrodes
influences the EI of the device. Fig. 7(a) shows the magnitude
of the impedance at each frequency for the PMN’s
and RBC’s
. Fig. 7(b) represents the corresponding phase information. Error bars on both graphs depict
one standard deviation. In these recordings, relatively small
channels were used such that PMN’s and RBC’s positioned
between the electrodes completely filled the lumen of the
channel. Differences between the device EI for the two cell
types are statistically significant. The resulting confidence
for the magnitude
interval was greater than 99.5%
and phase for all four of the frequencies depicted.
IV. DISCUSSION
Fabrication of the gold and epoxy-based photoresist structures on glass substrates used techniques similar to standard
Fig. 6. (a) Magnitude and (b) phase of the impedance for six microelectric
impedance devices when filled with a physiologic concentration of PBS (300
mOsm).
TABLE I
MICROCHANNEL/ELECTRODE DIMENSIONS OF THE SIX DEVICES TESTED
Device Number
1
2
3
4
5
6
Channel Width
(m)
10.5
10.5
10.5
10.1
10.5
10.5
Electrode Width
(m)
7.7
7.7
8.8
8.5
8.2
9.0
Electrode Gap
(m)
5.1
9.5
6.2
7.7
8.9
5.4
microlithography procedures using silicon wafers. Utilizing
the epoxy-based photoresist SU-8 enabled the fabrication of
microchannels for the gold electroplating with nearly perpendicular sideways and aspect ratios of 1 : 1 for photoresist
depths of 5 m. The resulting micro-EI devices have much
smaller electrode surface areas ( 32 m ) compared to recently reported efforts with planar devices and electrodes [1],
[2], [29]. This reduction in surface area allows for much
greater spatial resolution but also introduces electric field
fringe effects. By integrating the gold electrodes into the sides
of the microchannel, the limitations of planar technologies are
avoided and the resulting micro-EI devices can be incorporated
into numerous applications involving microfluidics. The threedimensional microchannels provide a repeatable geometry and
an efficient method for measuring EI differences of extremely
small material samples. The volume of fluid required to fill 150
m length of the microchannel is 6 pl, while the volume
required to fill the recording zone between the electrodes
is only 120 fl. The microchannel designs that gradually
tapered to 10 m in width (as seen in Fig. 3) demonstrated
AYLIFFE et al.: ELECTRIC IMPEDANCE SPECTROSCOPY USING MICROCHANNELS
(a)
(b)
Fig. 7. The (a) magnitude and (b) phase of the impedance for PMN’s
and RBC’s are shown at four selected frequencies. Error bars depict
one standard deviation. Differences between the two cell types in both
magnitude and phase are statistically significant (student t-test, < 0:005)
at all frequencies tested.
6
more predictable flow characteristics compared to channels
with square ends when small particles or cells were being
manipulated using pressure gradients. Preliminary experiments
manipulating and measuring the impedance of isolated erythrocytes and leukocytes have demonstrated applicability of this
technology to be used in future cellular studies such as cell
sorting, counting, or membrane biophysical characterization.
The magnitude and phase of EI versus frequency when the
recording zone is filled with varying concentrations of PBS, DI
water, and air (as seen in Fig. 5) demonstrate interesting lowfrequency characteristics. At the lowest frequency measured
(100 Hz), one might expect the resistive characteristics of the
PBS solutions to dominate, resulting in a phase angle of 0 . All
of the solutions measured, however, showed large capacitive
properties with negative phase angles up to 75 . The possibility of artifact is highly remote in that impedance sweeps
were conducted with various circuit elements of similar magnitude (resistors and capacitors) and measurements of nonionic
solutions generated expected results. These negative phase
55
angles are believed to be primarily due to the electrochemical
kinetics of ionic solutions with metal electrodes. The interface
between the metal electrodes and ionic solution is referred to
as the double layer and is often modeled using serial RC circuit
elements [30]–[32]. In some cases, the RC circuit models
can be tuned to closely approximate the double layer kinetics
of capacitors with large area-to-separation-distance ratios for
frequencies below 100 kHz [31], but parameter values depend
upon specific electrode and solution composition. At higher
frequencies, simple RC models cannot predict the frequency
dispersion that arises due to the relaxation time required for
adsorption-desorption of ions to the metal electrodes. The RC
values for the double layer are known to change by a factor of
three for every order of magnitude change in frequency [32].
The apparent resistive and capacitive effects of the double
layer heavily influence both the low frequency magnitude and
phase. As the frequency of the interrogating signal begins to
exceed 1 kHz, the solution resistance begins to dominate the
impedance magnitude and differences in ionic concentrations
can be easily measured.
The differences in the magnitude between the measured EI
spectra when the recording zone contained air, water, and
the four different concentrations of PBS were statistically
significant (Fig. 5). The calculated confidence intervals using
student -tests at four selected frequencies (10, 100, 500 k,
and 1 MHz) show that these microdevices have the capability
to discern a minimum of factor-of-two solution concentration
differences, near physiologic concentrations, of femtoliter volumes. The impedance measurements for DI water indicate that
the water may have absorbed some residual ions from the
microfabrication processes when it was added to the device.
The differences in magnitude between the solutions appeared
consistent between 1 kHz and 2 MHz. These data suggest
that optimization of the electrode material or surface coating
should improve the low frequency characteristics and possibly
the resolution capability of the developed micro-EI system.
The small, irregular shape of the gold electrodes prevented
the use of parallel-plate models to predict the behavior of the
overall device and may be attributing to the complexity of the
impedance curves. The significance of changes in geometry
is demonstrated by the variations in measured impedance
of physiologic concentrations of PBS for the six devices
tested (Fig. 6). The variability in device geometry should
be greatly reduced in a manufacturing environment. The
accurate determination of the dielectric properties of materials
measured in the micro-EI device currently requires more
sophisticated modeling to include the device geometry and
the electrochemical, double-layer effects.
The average whole-cell EI data presented in Fig. 7 demonstrates the potential to use micro-EI spectra to differentiate
between different cell types. The differences in both the
magnitude and phase of impedance were significant at all four
Because the raw EI spectra
frequencies tested
are comprised of numerous constituents, these data reflect
factors in addition to the electrical properties of the individual
cells. For example, the raw EI spectra are influenced by the
electrode/electrolyte interface impedance and the shunt path
impedance formed by the saline layer surrounding the cell.
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IEEE JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 8, NO. 1, MARCH 1999
Additional experimental and/or computational methods will
be required for applications interested in dielectric properties
of various cellular components.
V. CONCLUSION
Micromachining technologies have enabled the development of a micro-EI measurement system that can distinguish
l) quantities of
impedance differences in femtoliter (10
ionic solutions and single biological cells. The microdevices
were constructed from materials having excellent dielectric
and conductive properties to ensure highly sensitive impedance
measurements at frequencies up to 2 MHz. Constructing
the devices on planar glass substrates provided good optical properties and allowed continuous observation with light
microscopy. The overall EI of the resulting microstructures
were characterized with varying concentrations of phosphate
buffered saline solutions, air, and DI water placed between
the electrodes. Resulting impedance measurements demonstrated the ability to readily distinguish between solutions
with factor-of-two differences in ionic concentration over
the entire frequency range. In addition, the micro-EI system
demonstrated the potential for cell-sorting and counting.
ACKNOWLEDGMENT
The authors gratefully acknowledge the staff of HEDCO
Microfabrication Engineering Laboratory, Dr. V. Hlady, and
Dr. P. Tresco.
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H. Edward Ayliffe received the B.S. degree with High Honors in mechanical
engineering from Worcester Polytechnic Institute in 1989 and the Ph.D. degree
in bioengineering from the University of Utah in 1998.
Prior to his graduate studies at the University of Utah, he was employed
as a Research Engineer and Product Development Engineer with M.A.N.
Roland, Augsburg, Germany, and ALCOA, Denver, CO. He is currently
a Postdoctorate Fellow with HP Labs, Palo Alto, CA, working on the
miniaturization of product sensors. Concurrently, he is working with the
University of Utah’s Bioengineering Department to develop systems for
microelectric impedance spectroscopy of isolated living cells using MEMS
technology.
AYLIFFE et al.: ELECTRIC IMPEDANCE SPECTROSCOPY USING MICROCHANNELS
A. Bruno Frazier (S’85–M’85) received the B.S. and M.S. degrees in
electrical engineering from Auburn University in 1986 and 1987, respectively.
In December 1993, he received the Ph.D. degree in electrical engineering
from Georgia Institute of Technology.
From 1987 to 1990 he worked for Intergraph Corporation in the development of computer-aided graphics systems. His experience at Intergraph
Corporation ranged from the development of advanced printed circuitboard
technology as a Process Engineer to system design at the component level to
advanced packaging technologies for future CAD/CAM systems. From 1990
through 1993, he attended Georgia Institute of Technology and conducted
research into micromachining processes for the fabrication of metallic microstructures, development and characterization of micromachining materials,
as well as micromachined devices utilizing the previously developed processes
and materials. He was awarded the IShGM Educational Fellowship two
consecutive terms during his graduate studies. After graduating, he conducted
research in micromachining technologies at the University of Michigan
as a Visiting Scholar through June 1995. In August 195, he joined the
bioengineering and electrical engineering faculty at the University of Utah.
His current research interest is in the area of microinstrumentation including
biomedical, optical, magnetic applications of micromachining technology.
57
R. D. Rabbitt received the Ph.D. degree in applied
mechanics from Rensselaer Polytechnic Institute in
1986.
He is currently an Associate Professor of Bioengineering at the University of Utah with primary
research interests in auditory and vestibular end
organ physiology, microscale electric impedance
tomography, and analysis of nonlinear strain using
medical image data.
Dr. Rabbitt was awarded a Presidential Young
Investigator for his research on the mechanics of the
auditory system by the National Science Foundation shortly after graduating
from Rensselaer Polytechnic Institute.