title: Synthesis, spectral properties, and detection limits of reactive squaraine dyes, a new class of diode laser compatible fluorescent protein labels.
abstract: We describe the synthesis and spectral characterization of two reactive long-wavelength fluorescence labels (Sq635-m and Sq635-b), having either one or two N-hydroxysuccinimidyl esters. Both are squaraine derivatives and consist of a cyanine-type chromophore and a central squarate bridge. To improve water solubility, we introduced two sulfonic acid groups into the heterocyclic ring systems, and for covalent attachment to proteins, a reactive N-hydroxy-succinimide ester (NHS ester) was synthesized. The squaraine markers exhibit low quantum yields in water (phi = 0.15) and high quantum yields (phi = 0.6-0.7) when bound to proteins. The absorption maxima at 635 nm in water and at approximately 645 nm when bound to proteins allow excitation with commercially available diode lasers. The detection limit of a representative squaraine dye in blood was estimated to be half that of a commonly used fluorophore.
authors.affiliation: University of Regensburg, Institute of Analytical Chemistry, Chemo- and Biosensors, 93040 Regensburg, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Oswald
authors.forename: L
authors.initials: L
authors.lastname: Patsenker
authors.forename: J
authors.initials: J
authors.lastname: Duschl
authors.forename: H
authors.initials: H
authors.lastname: Szmacinski
authors.forename: O S
authors.initials: OS
authors.lastname: Wolfbeis
authors.forename: E
authors.initials: E
authors.lastname: Terpetschnig
mesh_terms: D000906:Antibodies / Q000097:blood; D001798:Blood Proteins / Q000032:analysis; D003500:Cyclization; D003503:Cyclobutanes / Q000097:blood / Q000138:chemical synthesis* / Q000737:chemistry; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D006801:Humans; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D012709:Serum Albumin / Q000276:immunology; D012710:Serum Albumin, Bovine / Q000032:analysis; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013388:Succinimides / Q000097:blood / Q000138:chemical synthesis* / Q000737:chemistry; D013451:Sulfonic Acids / Q000737:chemistry
chemical_list: D000906:Antibodies; D001798:Blood Proteins; D003503:Cyclobutanes; D005456:Fluorescent Dyes; D012709:Serum Albumin; D013388:Succinimides; D013451:Sulfonic Acids; C087581:squaraine-N-hydroxysuccinimide ester; D012710:Serum Albumin, Bovine; C001426:N-hydroxysuccinimide