Abstract
Novel pH-sensitive, water-soluble, long-wavelength fluorescent norsquaraine dyes and their barbituric and dicyanomethylene derivatives were synthesized and investigated. Some of these dyes contain a carboxylic functionality that was converted into an NHS ester to facilitate bio-conjugation. The absorption and emission spectra, fluorescence quantum yields, lifetimes, polarization, and photostabilities were measured free in solution and after binding to bovine serum albumin (BSA) and compared to those of conventional squaraines and the norcyanine dye CypHer5. Contrary to squaraines, norsquaraines are pH-sensitive but almost unaffected by the interaction with proteins. These dyes can potentially be used as fluorescent labels for biomedical applications, in particular for protein labeling, polarization-based assays, cell-based and pH-sensing measurements.
Published Version
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