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DyLight 550 Sulfhydryl-Reactive Dye

Label cysteines with this alternative to Alexa Fluor™ 555, Cy3™ and TRITC dyes.

DyLight 550 Sulfhydryl-Reactive Dye

Thermo Scientific DyLight 550 Sulfhydryl-Reactive Dye is a maleimide-activated derivative of high-performance DyLight 550 used to fluorescently label sulfhydryl-containing peptides, proteins and other biomolecular probes.

DyLight 550 provides vibrant orange-to-red fluorescence with better performance than other rhodamine derivatives including Alexa Fluor™ 555, TRITC and Cy3™ dye for fluorescent applications over a broad pH range (pH 4-9). The high water solubility of DyLight Fluors means that a high dye-to-protein ratio can be attained without causing precipitation of the conjugates.


  • High performance – DyLight 550 shows brighter fluorescence than Alexa Fluor 555, TRITC and Cy3 dye
  • Specific – maleimide-activated dye labels proteins and other molecules at reduced sulfhydryls (-SH)
  • Efficient labeling methods – well-characterized chemistry and optimized protocols provide for reliable, high-quality labeling
  • Optimized antibody labeling procedure –complete protocol for IgG reduction and labeling and calculating the labeling efficiency


  • Antibody labeling for immunofluorescence applications, including immunocytochemistry (ICC), immunohistochemistry (IHC), Western blotting and ELISA assay
  • Target macromolecule labeling for in vitro and in vivo fluorescent detection strategies

Product Details:

Fluorescence detection of DyLight 550 dye
Immunofluorescence microscopy using DyLight 550 dye. Cytokeratin 18 (green) and lamin B1(red) in U2OS cells were detected with the respective primary antibodies and goat anti-mouse and anti-rabbit secondary antibodies labeled with DyLight 550 and 650 Microscale Antibody Labeling Kits, respectively.

DyLight 550 Sulfhydryl-Reactive Dye is activated with a maleic acid imide (maleimide) moiety to form a reactive alkylation reagent. Labeling occurs through reaction of the maleimide-activated dye with reduced sulfhydryl groups (-SH) to form stable thioether bonds. Maleimides are specific for sulfhydryl groups between pH 6.5-7.5. Learn more about maleimide chemistry.

Related Resources:

DyLight 550 Fluorophore Overview Page
Complete DyLight Fluor Product Guide

Related Products:

All Fluorescent Labeling Reagents and Kits
DyLight Fluor Secondary Antibody Conjugates
DyLight Fluor Streptavidin and NeutrAvidin Conjugates
Krypton Fluorescent Protein Stains

Ordering Information
Product # Description Pkg. Size Instructions MSDS CofA Price
62290 DyLight 550 Maleimide
Formulation: Maleimide activated proprietary orange fluorescent dye
Sufficient For: 1 use to label a total of 7mg of IgG using typical conditions
1mg Product Instructions for product #62290 DyLight 550 Maleimide MSDS for product #62290 DyLight 550 Maleimide Certificate of Analysis for product #62290 DyLight 550 Maleimide $262.00

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Instructions | MSDS | CofA
Product Instructions | MSDS | CofA  

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