Phycoerythrin (PE)-Cy7-conjugated anti-human primary antibodies are near-infrared tandem fluorochrome reagents extensively employed in high-parameter flow cytometry and fluorescence-based cellular analysis. PE-Cy7 combines the exceptional brightness of R-phycoerythrin with the far-red emission of the cyanine dye Cy7, producing a tandem conjugate that is optimally excited by the 488 nm, 532 nm, or 561 nm laser lines and emits in the near-infrared region. This spectral configuration makes PE-Cy7 particularly valuable for detecting low-abundance human antigens and for designing multicolor panels that require minimal spectral overlap with other fluorophores.

The PE-Cy7 Tandem Fluorophore

PE-Cy7 is a tandem fluorochrome that operates through Förster resonance energy transfer (FRET). The tandem consists of two covalently linked fluorophores: R-phycoerythrin (R-PE), a large phycobiliprotein derived from red algae with a molecular weight of approximately 240,000 daltons, serving as the donor molecule, and a cyanine dye (Cy7) acting as the acceptor. The donor PE absorbs light at 488–565 nm and transfers the excitation energy non-radiatively to the acceptor Cy7, which then emits fluorescence in the near-infrared region. This FRET mechanism produces a large Stokes shift of approximately 300 nm, enabling the use of a single blue or green laser for excitation while detecting emission in a far-red channel.

Spectral Properties

PE-Cy7 exhibits an excitation maximum at 565 nm, corresponding to the absorption characteristics of the PE donor, with secondary excitation at approximately 496 nm. The emission maximum of the Cy7 acceptor is at 778–785 nm, with a commonly cited value of 778 nm. The Stokes shift is approximately 213–300 nm, depending on the specific tandem preparation and measurement conditions.