Degree of labeling (DOL) describes the number of fluorophores per antibody. For in vivo labeling experiments, the DOL is restricted to a narrow range because it has significant consequences for the biodistribution and clearance of the probe. For example, for in vivo imaging, we have determined that the DOL range for the far-red Alexa Fluor dyes is 1.5 to 3 molecules per antibody for optimal optical in vivo imaging.
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