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a
b
Sample
Type
A
Type
B
Type
C
dichroic
mirror
Mixture
λ
2
detector
filter
c
1
2
3
4
N
Magnet
S
Imaging system
Fig. 6 (a) Schematic illustration of a flow cytometer used in a suspension array. The sample
microspheres are hydrodynamically focused in a fluidic system and read-out by two laser beams.
Laser 1 excites the encoding dyes and the fluorescence is detected at two wavelengths. Laser 2 is
used to quantify the analyte. (b) Scheme of randomly ordered bead array concept. Beads are
pooled and adsorbed into the etched wells of an optical fiber. (c) Scheme of randomly-ordered
sedimentation array. A set of encoded microspheres is added to the analyte solution. Subsequent to
binding of the analyte, microparticles sediment and assemble at the transparent bottom of a sample
tube generating a randomly ordered array. This array is evaluated by microscope optics and a
CCD-camera. Reproduced with permission from Refs. [
85
] and [
101
]. Copyright 1999, 2008
American Chemical Society
number of codes depends on the number of different dyes and concentrations
(
N
m
(where
C
is the number of
codes,
N
is the number of intensity levels and
m
is the number of colors). For
example, fluorescently encoded microbeads (
Ø
5.6
¼
intensity level) according to the formula:
C
¼
m, available from Luminex
Corporation,
http://www.luminexcorp.com
) doped with an orange and a red fluo-
rescent dye at ten different concentrations yield in 100 different bead families and
m
500 bead families are created by staining with three dyes. Fluorescence intensity
is the standard parameter that is used for identification. The number of codes can be
increased by measuring the luminescence lifetime as demonstrated by Keij and
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