A broad array of imaging and diagnostic
technologies employs fluorophore-labeled
antibodies for biomarker visualization,
an experimental technique known as immunofluorescence. Significant
performance advantages, such as higher signal-to-noise ratio, are
gained if the appended fluorophore emits near-infrared (NIR) light
with a wavelength >700 nm. However, the currently available NIR
fluorophore
antibody conjugates are known to exhibit significant limitations,
including low chemical stability and photostability, weakened target
specificity, and low fluorescence brightness. These fluorophore limitations
are resolved by employing a NIR heptamethine cyanine dye named s775z
whose chemical structure is very stable, charge-balanced, and sterically
shielded. Using indirect immunofluorescence for imaging and visualization,
a secondary IgG antibody labeled with s775z outperformed IgG analogues
labeled with the commercially available NIR fluorophores, IRDye 800CW
and DyLight800. Comparison experiments include three common techniques:
immunocytochemistry, immunohistochemistry, and western blotting. Specifically,
the secondary IgG labeled with s775z was 3–8 times brighter,
3–6 times more photostable, and still retained excellent target
specificity when the degree of antibody labeling was high. The results
demonstrate that antibodies labeled with s775z can emit total photon
counts that are 1–2 orders of magnitude higher than those currently
possible, and thus enable unsurpassed performance for NIR fluorescence
imaging and diagnostics. They are especially well suited for analytical
applications that require sensitive NIR fluorescence detection or
use modern photon-intense methods that require high photostability.