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CASY TT Operator‘s Guide
1.3 Viability Determination using Electrical Current Exclusion
The CASY Systems use a label-free, non-invasive method, called the Electrical Current Exclusion
method, for measuring cell viability of mammalian cell lines. Viability determination may also be
possible with, for example, algae.
Like with well known dye-based assays this viability determination depends on the membrane
integrity of the cells. Since intact cells have intact cell membranes, they can generally be considered
as electrical isolators and an increased level of resistance is achieved over the measuring pore.
This increase in resistance is a dimension for the volume of the cells. They are measured with their
true cell volume. In contrast, dead cells whose membranes no longer act as an electrical barrier are
recorded mainly by the size of their cell nucleus (see Figure 4). In order to guarantee the ability for
viability determination, it is important that the cells pass through the pore individually.
Figure 4: Viability determination of an animal cell line using the electrical current exclusion method.
Normalization and Evaluation Cursors
Since the volume of the cell nucleus is significantly smaller than the volume of the entire cell, the
populations “debris”, “dead cells”, and “viable cells” can be clearly distinguished in the high-resolu-
tion size distribution. For calculating the viability in the analyzed suspension, two pairs of cursors
are available to define specific size ranges and to calculate the percentage of viable cells.
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The counts in the size range of the normalization cursors define the total cell number and are
normalized to represent 100%.
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The counts in the evaluation cursor range define a part of the total cell number used to calculate
a percentage.
Therefore, viability is calculated by setting the normalization cursor range such that it includes the
dead and viable population, whereas the evaluation cursor range includes the viable population
only. Based on these settings the, CASY Cell Counter and Analyzer calculates the viability in %.
If objects with the same volume as dead cells are additionally present in the suspension to be ana-
lyzed, they are recorded in the size range of dead cells as well, and therefore viability determination
is not possible. The reason is that these objects would further increase the number of total cells,
which would incorrectly lower the viability.
For more information on using the normalization and evaluation cursors, see section
Setting the Measuring Range and the Cursor Positions
and as well as videos and guides on www.cell-
counting.de.
Viability Determination using Electrical Current Exclusion
