Biomedical Engineering Reference
In-Depth Information
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Figure 5.4
The principle of the ECIS system.
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(Reprinted by kind permission of Nature Publishing Group.)
capacity through detection of the spatial distribution of the displacement
current (Figure 5.5). Cellular interrogation takes place at frequencies between
10 kHz and 1MHz. The system can be adapted to work under a microscope and
also facilitates the applications of chemical solutions by microinjection. Appli-
cations range from synaptic transmission, ion channel activity, cell division and
growth to protein-based electromotility and membrane flexoelectricity.
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The
technique is essentially a miniaturization of electrical impedance tomography,
which is an imaging method that uses a harness of electrodes around the human
torso, for example, to visualize the organs based on the specific impedance of
each human tissue. Unlike the situation where ionizing radiation is employed,
such as involved with X-ray imaging, impedance tomography is a much gentler
method and can be applied without serious, medical side effects.
An integrated cell biochip microsystem platform based on bioimpedance
measurements has been developed at the Tyndall National Institute in Ireland.
The platform combines mixed sensor technologies with microfluidics capa-
bilities, enabling multi-parameter detection.
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Optical imaging and electrical (impedance) detection, pH, temperature and
dissolved oxygen sensors and microfluidics are all integrated into the system.
Impedance measurements are performed on inter-digitated electrode structures
(IDES) of 20 mm width and 10 mm gaps, fabricated using indium tin oxide (ITO)
chosen as biosensor material due to its optical transparency, electrical char-
acteristics and biocompatibility. The fluidic capabilities allow cell media to be
delivered to each of the system's six modules, enabling chemicals to be delivered
to the cells. Concentration, growth and alterations of the physiological state of
cells can be detected as impedance changes. The system yields information
about spreading, attachment and morphology of cells. Figure 5.6 shows an
image of an ITO biochip surface plated with live cells. The effect of phar-
maceutical drugs and neurotoxins can be studied. The technology uses
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