Water-soluble NIR fluorescent probes based on squaraine and their application for protein labeling

Keitaro Umezawa, Daniel Citterio, Koji Suzuki

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47 Citations (Scopus)


Water-soluble near-infrared (NIR) fluorescent labeling probes, named KSQ-3 and -4, which are based on a squaraine backbone, were synthesized and applied to biological labeling. The presented results demonstrate that the large, planar and hydrophobic squaraine dye becomes fully soluble in aqueous solution by the introduction of several sulfo group terminated alkyl substituents. Especially KSQ-4, which is substituted with four sulfo groups, exhibited perfect water solubility and significant fluorescence emission at the NIR region (817 nm) in the presence of bovine serum albumin (BSA). BSA was covalently labeled with KSQ-4, and the conjugate showed a strong absorption peak at 787 nm, which indicates compatibility with commercially available NIR laser diodes used for exciting the fluorophore. Furthermore, strong fluorescence emission was observed at 812 nm (φ = 0.08). 2008

Original languageEnglish
Pages (from-to)213-217
Number of pages5
JournalAnalytical Sciences
Issue number2
Publication statusPublished - 2008 Feb


ASJC Scopus subject areas

  • Analytical Chemistry

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