Description
Fluorescein-5/6-Isothiocyanate (5/6-FITC) – Classic Amine-Reactive Dye for Fluorescent Labeling
5/6-FITC is a widely used amine-reactive fluorescein dye for covalent labeling of proteins and alkylamino-modified nucleic acids. With strong absorption at 494 nm and emission at 518 nm, it is ideally suited for flow cytometry (FACS) and confocal laser scanning microscopy, especially due to its spectral compatibility with the 488 nm line of the argon-ion laser.
Fluorescein derivatives such as 5/6-FITC are known for their high quantum yield, excellent water solubility, and stable conjugation properties, forming thiourea bonds via their isothiocyanate group. This reagent is a reliable standard in fluorescent biomolecule labeling workflows.
Performance Highlights
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Amine-reactive fluorescein dye for stable thiourea linkage
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Optimal excitation/emission at 494 nm / 518 nm
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Compatible with 488 nm argon-ion laser – ideal for FACS and microscopy
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High fluorescence quantum yield and water solubility
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Suitable for proteins and alkylamino-modified oligonucleotides
Properties
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CAS Number: 27072-45-3
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Molecular Weight: 389.38
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Empirical Formula: C₂₁H₁₁NO₅S
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Absorption [λmax]: 494 ± 3 nm
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Emission [λmax]: 518 ± 3 nm
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Extinction Coefficient (ε): >70,000 M⁻¹·cm⁻¹
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Reactive Moiety: Isothiocyanate (reacts with 1° amines to form thiourea bonds)
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Solubility: DMSO, DMF
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Appearance: Orange powder
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Storage: −20 °C, dry, protected from light (especially in solution)
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Fluorescence Reading Buffer: T&S Buffer, pH 9
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Trade Name: 5/6-FITC (mixed isomers)
Applications
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Flow cytometry (FACS)
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Confocal laser scanning microscopy
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Fluorescent labeling of proteins and nucleic acids
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Biomarker detection and cellular imaging
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Development of fluorescent probes and assays
