Description
5/6-FAM-SE: Mixed-Isomer Fluorescein Labeling Reagent for Versatile Bioconjugation
5/6-Carboxyfluorescein NHS Ester (5/6-FAM-SE) is an amine-reactive fluorescent dye widely used for covalent labeling of proteins and alkylamino-modified nucleic acids. This mixed-isomer fluorescein derivative is well-suited for confocal microscopy and flow cytometry due to its strong spectral match with the 488 nm argon-ion laser line. With high absorptivity, excellent quantum yield, and good solubility, 5/6-FAM-SE enables reliable labeling for a wide range of fluorescence-based applications.
Performance Highlights
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Bright green fluorescence with excitation/emission at 496 nm / 517 nm
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Efficient conjugation via NHS ester to primary amines
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High extinction coefficient (>70,000 M⁻¹·cm⁻¹) and excellent quantum yield
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Stable in aqueous buffer; low risk of precipitation when conjugated
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Compatible with standard biomolecule labeling workflows
Properties
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Molecular Weight: 473.39
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Empirical Formula: C₂₅H₁₅NO₉
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CAS Number: 117548-22-8
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Absorption [λmax]: 496 ± 3 nm
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Excitation [λmax]: 493 ± 3 nm
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Emission [λmax]: 517 ± 3 nm
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Excitation Source: 488 nm (argon-ion laser)
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Extinction Coefficient (ε): >70,000 M⁻¹·cm⁻¹
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Reactive Moiety: NHS ester (reacts with 1° amines to form stable amide linkages)
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Solubility: Acetonitrile, Acetone
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Buffer for Fluorescence Readings: T&S Buffer, pH 9
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Appearance (form/color): Yellow-orange solid (powder)
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Storage: −20 °C, dry, and protected from light
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Trade Names: 5/6-Carboxyfluorescein-NHS-Ester, 5/6-FAM-SE, 5-(and 6)-carboxyfluorescein succinimidyl ester (mixed isomers)
Applications
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Fluorescent labeling of antibodies and other amine-containing biomolecules
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Protein detection in cast gels and Western blot membranes
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Flow cytometry (FACS)
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Confocal laser scanning microscopy
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General bioconjugation tasks in research and diagnostics
