GenePix 4000B Microarray Scanner User Guide
5000450 D
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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 GenePix
4000B Microarray Scanner has a dynamic range of 10
4
. Dynamic range
is determined primarily by the design of the PMT. In the 4000B
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_4000B.book Page 31 Friday, October 22, 2010 3:07 PM
