Cyanine 5 is a popular indocyanine fluorophore that exhibits low, non-specific binding and relatively pH-independent fluorescence. This NHS ester version allows for post-deprotection labeling, and unlike the phosphoramidite version, contains 2 sulfonate substitutions directly on the indocyanine nuclei. The sulfonates make the Cyanine 5 less susceptible to aggregation and do not significantly change the fluorescent properties of the dye.
Coupling: For labeling 0.2 µmoles of an amino-modified oligonucleotide, dissolve 3.9 mg of the sulfoCyanine 5 NHS Ester in 100 µL DMSO (or DMF). Dissolve the amino-modified oligonucleotide in 500 µL 0.1 M carbonate/bicarbonate buffer (pH 9). Add 20 µL of the NHS Ester solution and vortex. Let react for 60 min at room temperature and desalt.