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DyLight 650 Sulfhydryl-Reactive Dye

A bright cysteine-labeling alternative to Alexa Fluor™ 647 and Cy5™ dyes.

DyLight 650 Sulfhydryl-Reactive Dye

Thermo Scientific DyLight 650 Sulfhydryl-Reactive Dye is a maleimide-activated derivative of high-performance DyLight 650 used to fluorescently label sulfhydryl-containing peptides, proteins and other biomolecular probes.

DyLight 650 provides vibrant far-red fluorescence with comparable or improved performance over other dyes, including Alexa Fluor™ 647 and Cy5™ dye, 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 650 fluoresces brighter than Alexa Fluor 647 and Cy5
  • 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:

Fluorescent detection of cytokeratin 18 in A549 cells with DyLight 650 by epifluorescence microscopy
Immunofluorescence microscopy using DyLight 650 dye. Intermediate filaments (red) in A549 cells were fluorescently labeled with biotinylated mouse anti-cytokeratin 18 antibody and DyLight 650-Conjugated Streptavidin. Nuclei were labeled with Hoechst dye.

DyLight 650 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 650 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
DyLight 650 Azide-Reactive Dye – phosphine-activated fluorescent dye for Staudinger ligation
Krypton Fluorescent Protein Stains

Ordering Information
Product # Description Pkg. Size Instructions MSDS CofA Price
62295 DyLight 650 Maleimide
Formulation: Maleimide activated proprietary far-red fluorescent dye
Sufficient For: 1 use to label a total of 7mg of IgG using typical conditions
1mg Product Instructions for product #62295 DyLight 650 Maleimide MSDS for product #62295 DyLight 650 Maleimide Certificate of Analysis for product #62295 DyLight 650 Maleimide $262.00

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Instructions | MSDS | CofA
Product Instructions | MSDS | CofA  

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