The isomer-free, amine-reactive Alexa Fluor 750 carboxylic acid, succinimidyl ester and its conjugates have spectra similar to that of Cy7 dye. As the longest-wavelength Alexa Fluor dye, the emission is well separated from commonly used far-red fluorophores such as Alexa Fluor 647 dye or allophycocyanin (APC), facilitating multicolor analysis. Fluorescence of this long-wavelength Alexa Fluor dye is not visible to the human eye but is readily detected by most imaging systems. A 5 mg unit size (A-20111) is also available.