DyLight™ PEGylated dyes display absorption spectra ranging from 550 nm to 783 nm. These reagents fluoresce over a broad pH range, are more intense than Alexa Fluor® or Cy® dyes in many applications and match the output wavelengths of common fluorescence instrumentation. Additionally, the water solubility of the DyLight™ reagents allows a high dye-to-protein ratio without precipitation during conjugation.

The PEGylated DyLight™ dyes are derivatives of corresponding high-performance non-PEGylated DyLight™ dyes, which are used to fluorescently label antibodies and proteins. Conjugates made with PEGylated DyLight™ dyes are effective molecular probes that can be used in cellular imaging and other fluorescence detection methods. These DyLight™ dyes contain two to four non-toxic polyethylene glycol (PEG) chains. The PEG chains enhance fluorescence and reduce non specific binding of conjugates, improve solubility of the dyes and labeled molecules in aqueous solution, aid in cell permeability, and improve retention, notably in tumours. The near-infrared (NIR) to far-red fluorescence properties of some of the PEGylated dyes such as DyLight 680-4xPEG and DyLight 755 make them useful in biological, chemical and pharmaceutical applications, including in vivo imaging.

The amine-reactive dyes contain N-hydroxysuccinimide (NHS) esters, the simplest and most commonly used reactive group for labeling proteins. NHS esters react with primary amines on the protein, forming a stable, covalent amide bond and releasing the NHS group.

The sulphhydryl-reactive fluors contain maleimide groups that react predominantly with free –SH groups at pH 6,5 to 7,5, forming a stable thioether bond. At pH 7, the maleimide group is ~1000 times more reactive toward a free sulfhydryl than to an amine. At pH values >7,5, reactivity towards primary amines increases and hydrolysis of the maleimide group can occur.