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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 con-
taining microchannels with integrated gold electrodes were fab-
ricated to enable EI measurements of femtoliter (10) 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 moni-
toring 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, microma-
chine, spectroscopy.
I. INTRODUCTION
ELECTRIC
impedance
(EI) measured
in
a one-
dimensional
(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 demon-
strated the ability to sense variations in solution tempera-
tures, ionic concentrations, hydrogen peroxide concentrations,
and even antigen-antibody bindi