CypHer7E maleimide is an excellent building block for developing site-specific pH probes. It can be readily conjugated to thiol-containing biomolecules (such as antibodies, peptides and thiol-modified oligos). It is analogous to CypHer5E maleimide with much longer excitation and emission. It is one of the very few acidotropic pH probes that exhibit NIR fluorescence. CypHer7E is a NIR pH-sensitive cyanine dye derivative that can be used to study most classes of cell surface receptors which internalize into the endocytic pathway when activated by a ligand. CypHer7E maleimide is a flexible, generic fluorophore that can be coupled to a receptor or epitope tag antibody and monitors neutral to acidic intracellular events.