15
Overview
A
A
Introduction
RTCA SP Instrument
Derivation of the Cell Index (CI)
A unitless parameter termed Cell Index (CI) is derived to measure the relative change in
electrical impedance to represent cell status. e CI is a relative and dimensionless value
since it represents the impedance change divided by a background value. When there are
no cells present in the medium, the sensor’s electronic property will not be a ected and
the impedance will be small as shown in Figure 1 when Z = Z
0
.
When there are more cells on the electrodes, the impedance will be larger. e CI
calculation is based on the following formula: CI = (Z
i
– Z
0
)/15 Ω, where Z
i
is the
impedance at an individual point of time during the experiment, and Z
0
is the impedance
at the start of the experiment. us the CI is a self-calibrated value derived from the ratio
of impedances. For more detailed information on how to derive the CI, please refer to the
Monitor the Experiment section in the RTCA So ware Manual. Several features of the CI
are summarized:
When cells are not present or are not well-adhered on the electrodes, then the CI is
about zero.
Under the same physiological conditions, when more cells are attached on the
electrodes, then the CI values are higher. In this case, CI is a quantitative measure of
the cell number present in a well.
Additionally, a change in a cell status, such as cell morphology, cell adhesion or cell
viability can lead to a change in CI.
e measurement of impedance is a non-invasive method in relation to the cells, and only
a very weak electrical signal is applied to the sensor electrodes. e AC excitation voltage
level is in the mV range and the resulting current is in the µA range so that individual wells
in a plate can be interrogated repeatedly over a wide interval range throughout the experi-
ment. Chemical compounds or other reagents can be added at any time and monitored
continuously in hours or days. Unlike “end point” assays, the system allows an investigator
to monitor the entire course of the experiment in real time without any interruption.
e RTCA SP Instrument consists of the following main components:
RTCA Control Unit
RTCA Analyzer
E-Plate 96
RTCA SP Station
Figure 2: The RTCA SP Instrument with the main components: RTCA Analyzer, RTCA SP Station, E-Plate
96 and RTCA Control Unit.
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