GenePix 4100A Microarray Scanner User Guide
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Dynamic Range and Detection Limit
The dynamic range of an instrument is the range of signal values over
which the instrument can accurately measure change. The 4100A
Microarray Scanner has a dynamic range of 10
4
. Dynamic range is
determined primarily by the design of the PMT. In the 4100A Microarray
Scanner, the voltage (gain) applied to the PMT can be adjusted to
change the amplification of the signal as electrons pass through the
PMT. The optimum working range is 400 V to 1000 V. If the gain is set
below this range, the probability that each impinging photon will be
converted to an electron is diminished, and the dynamic range will be
limited on the low end. Above this range, noise begins to interfere with
accurate signal measurement. Both of these cases will limit the
dynamic range.
The dynamic range of an instrument is often considered in conjunction
with its detection limit. The detection limit is defined as the dye
concentration for which the signal-to-noise ratio = 3. Signal-to-noise
ratio is calculated as:
(Signal – Background) / Standard Deviation of Background
Although you might be able to see features below this level, the
quantitative accuracy diminishes significantly.
GenePix_4100A.book Page 31 Friday, October 22, 2010 3:21 PM
