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SO
3
-
SO
3
-
-
O
3
S
SO
3
-
N
N
+
Cy5.5
O
-
O
3
S
SO
3
-
N
N
+
Cy7
O
SO
3
-
O
-
O
3
S
SO
3
-
N
N
+
800CW
SO
3
-
O
Figure 9.2 Examples of near-infrared cyanine fluorophores commonly used for labeling
macromolecules: Cy5.5, Cy7 (GE-Healthcare Life Sciences, Piscataway NJ), and IRDye
800CW (Li-COR Corp., Lincoln NE).
side chains. Some sulfated dyes display inherently low self-quenching even
after covalent linking to polypeptides, for example, green fluorescent Alexa
Fluor 488. Such dyes have many advantages over traditionally used fluores-
cein analogs for microscopy applications. However, for the reasons that were
described in previous sections of this review,
in vivo
fluorescence imaging
currently relies on fluorophores with far-red to NIR emission.
The linking of NIR fluorophores to plasma proteins has advantages and
pitfalls: the advantages include availability of purified or recombinant blood
plasma proteins, near-uniform mass, near-constant number of reactive
groups, and low immunogenicity in a native form. The disadvantages in-
clude the limited number of above reactive groups, insufficiently long
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