Description
5-FMI: Thiol-Reactive Fluorescein Dye for Targeted Bioconjugation
Fluorescein-5-maleimide (5-FMI) is a thiol-reactive fluorescein derivative specifically designed for the selective labeling of cysteine residues in proteins and thiol-modified oligonucleotides. This dye enables the formation of stable thioether bonds through maleimide-thiol conjugation, delivering bright green fluorescence suitable for a wide range of fluorescence applications in research and diagnostics.
Performance Highlights
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Selective and stable conjugation to thiol groups
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Bright green fluorescence (Ex/Em: 492 nm / 513 nm)
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High molar absorptivity (>80,000 M⁻¹·cm⁻¹)
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Excellent reactivity with cysteine residues or thiol-modified oligos
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Well-suited for labeling in aqueous or organic solvent systems
Properties
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Molecular Weight: 427.4
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Empirical Formula: C₂₄H₁₃NO₇
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CAS Number: 75350-46-8
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Absorption [λmax]: 492 ± 3 nm
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Emission [λmax]: 513 ± 3 nm
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Extinction Coefficient (ε): >80,000 M⁻¹·cm⁻¹
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Reactive Moiety: Maleimide (reacts with thiol to form stable thioether linkage)
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Solubility: DMF
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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: Fluorescein-5-maleimide, 5-FMI
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Chemical Name: 5-(2,5-Dioxo-2,5-dihydro-pyrrol-1-yl)-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)-benzoic acid
Applications
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Site-specific fluorescent labeling of cysteine-containing proteins
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Bioconjugation of thiol-modified oligonucleotides
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Fluorescence-based detection and imaging
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Redox-sensitive probe development
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Targeted fluorescence assays in biochemistry and molecular biology
