Heptamethine cyanines
are broadly used for a range of near-infrared
imaging applications. As with many fluorophores, these molecules are
prone to forming nonemissive aggregates upon biomolecule conjugation.
Prior work has focused on persulfonation strategies, which only partially
address these issues. Here, we report a new set of peripheral substituents,
short polyethylene glycol chains on the indolenine nitrogens and a
substituted alkyl ether at the C4′ position, that provide exceptionally
aggregation-resistant fluorophores. These symmetrical molecules are
net-neutral, can be prepared in a concise sequence, and exhibit no
evidence of H-aggregation even at high labeling density when
appended to monoclonal antibodies or virus-like particles. The resulting
fluorophore–biomolecule conjugates exhibit exceptionally bright in vitro and in vivo signals when compared
to a conventional persulfonated heptamethine cyanine. Overall, these
efforts provide a new class of heptamethine cyanines with significant
utility for complex labeling applications.
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