Bio-Rad Bio-Plex System Validation and Calibration Tools - Manual (Page 8)

Impact on Assay Performance
The slope of the regression line is directly related to the dynamic range of the
instrument. The slope yields direct information about the response of the
photomultiplier tube. If the photomultiplier tube signal saturates at low
fluorescence values, the dynamic range of the instrument is affected. The slope
of the line impacts the dynamic range and the range, in turn, impacts the
quantifiable range of an assay.
Instrument Threshold (Sensitivity)
Definition
Every instrument has an inherent level of background noise. Noise can be
attributed to the laser, the PMT, the amplification electronics or the fluidics. The
instrument threshold (sensitivity) of the Bio-Plex array reader is one way to
demonstrate noise of the system. It is defined as the reporter channel signal of a
blank bead that contains no reporter dye.
Impact on Assay Performance
The instrument threshold level demonstrated using the Bio-Plex validation kit is a
low fluorescence intensity value. The typical background or zero standard of a
Bio-Plex cytokine assay falls at a median fluorescence intensity of ~100. This is a
desired result, as the instrument threshold should not limit the assay sensitivity. If
the instrument threshold is too close to zero, then a low assay signal may be
masked; if too high, then the linearity and dynamic range may be compromised.
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