Probing Interactions at the Nanoscale: Sensing Protein Molecules Page: 4 of 7
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A NOVEL HIGH-FREQUENCY SENSOR FOR
T. C. Messina,' L. N. Dunkleberger,' G. A. Mensing,2 A. S. Kalmbach3, R.
Weiss3, D. J. Beebe,2 and L. L. Sohn'
'Department of Mechanical Engineering, University of California-Berkeley,
Department of Biomedical Engineering, University of Wisconsin-Madison,
Department of Electrical Engineering, Princeton University
We have developed a high-frequency electronic biosensor for probing molecules and
cells. We use microfluidic tectonics (pFT) to create a 3-dimensional parallel-plate
device that results in enhanced electronic coupling to sample volumes as small as
picoliters over a frequency range of 0.05-40 GHz. In this frequency range, we are able
to access two distinct regimes, a- and P-dispersion. The former corresponds to
permittivity enhancement due to rearrangement of small ions, including screening at the
fluid interface, and the latter arises from distortions of cellular membranes and
macromolecules. Here we report experiments differentiating polymerase chain reaction
(PCR) products before and after amplification cycling.
Keywords: dielectric spectroscopy, microfluidics, electronic biosensing
The need for rapid characterization of molecular and biological materials is extremely
important for research, clinical, and defense applications. Most current optical and
chemical techniques are effective for analyzing such specimen [1-3]; however, they
often require chemical modification. Furthermore, they can be time-constrained due to,
for example, photobleaching of fluorophores Recently, purely electronic techniques such
as capacitance cytometry  and microwave spectroscopy [5-8], as well as fourier-
infrared spectroscopy [9,10], have offered viable solutions to these issues whilst probing
a range of length and time scales for very small sample volumes.
In this report, we discuss our development of a microwave-frequency-based biosensor
of parallel-plate geometry that is embedded within a microfluidic device. This biosensor
allows us to perform dielectric spectroscopy on a variety of biological samples-from
cells to molecules-in solution. Because the device is purely electronic, the sensor
allows for rapid characterization with little sample preparation or chemical alteration. In
addition, this biosensor is capable of probing length scales from millimeters to microns
over a frequency range 50 MHz to 40 GHz, and sample volumes as little as picoliters
[4,5]. Our high-frequency biosensor has evolved from previous device designs based on
a coplanar waveguide (CPW) geometry, where we measured changes within the plane of
the CPW device . For our current device, we extend the center conductor of the CPW
and employ microfluidic tectonics (pFT)  to embed two CPW devices within a
7th International Conference on Miniaturized Chemical and Biochemical Analysis Systems
October 5-9, 2003, Squaw Valley, California USA
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Sohn, Lydia; Weiss, Ron & Tavazoie, Saeed. Probing Interactions at the Nanoscale: Sensing Protein Molecules, report, September 15, 2003; United States. (https://digital.library.unt.edu/ark:/67531/metadc896815/m1/4/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.