Streptavidin, (R-PE)

Invitrogen™ Streptavidin, R-Phycoerythrin Conjugate (SAPE) combines the high-affinity biotin-binding capability of streptavidin with the exceptional brightness of R-phycoerythrin (R-PE), enabling sensitive fluorescent detection of biotinylated antibodies, proteins, nucleic acids, and other biomolecules.

Widely used in flow cytometry, multiplex immunoassays, microarrays, and fluorescent immunoassays, Streptavidin-RPE contributes strong signal intensity for applications requiring detection of low-abundance targets and precise measurement of cellular biomarkers.

Streptavidin-RPE is commonly used for flow cytometry, quantitative flow cytometry, antigen density measurement, receptor occupancy assays, target engagement analysis, multiplex immunoassays, and fluorescent detection of biotinylated molecules.

Why use Streptavidin-RPE?

The combination of streptavidin and R-phycoerythrin results in a sensitive and flexible detection system for biotinylated targets across a broad range of research applications.

Key advantages include:

• Exceptional fluorescence intensity for detecting low-expression targets
• High-affinity streptavidin-biotin interaction for reliable target detection
• Strong signal-to-noise performance
• Broad dynamic range for quantitative measurements

The brightness of R-PE is particularly valuable in applications where accurate quantification, rare event detection, or low-level target measurement is required.

Applications

Streptavidin-RPE is used across a diverse set of research and analytical workflows that rely on sensitive detection of biotinylated molecules.

Flow cytometry

Detect biotinylated antibodies for immunophenotyping, cell characterization, biomarker analysis, and immune monitoring. The strong fluorescent signal generated by R-PE supports clear population separation and robust assay performance.

Multiplex bead-based immunoassays

Serve as a fluorescent reporter molecule in multiplex protein detection assays used for cytokine analysis, biomarker discovery, and translational research.

Microarrays

Detect biotinylated probes and targets in gene expression, protein expression, and genotyping workflows.

Fluorescence immunoassays

Enable sensitive detection in fluorescent ELISA, ligand-binding assays, and other fluorescence-based protein analysis workflows.

Rare cell detection

Support identification and characterization of low-frequency cellular populations, including rare immune subsets, circulating tumor cells, and minimal residual disease populations.

Antigen-specific immune monitoring

Facilitate detection of antigen-specific T cells through MHC tetramer and multimer-based assays used in immunology, vaccine, and immunotherapy research.

Quantitative flow cytometry

Traditional flow cytometry is often used to determine whether a biomarker is present or absent. Quantitative flow cytometry extends this capability by enabling measurement of protein expression levels on individual cells.

Because R-PE is among the brightest fluorophores available, Streptavidin-RPE is frequently incorporated into quantitative flow cytometry workflows that require accurate measurement across a wide range of expression levels.

Researchers frequently use quantitative flow cytometry to generate metrics such as Antibody Binding Capacity (ABC), Molecules of Equivalent Soluble Fluorochrome (MESF), and estimated receptor molecules per cell.

Antigen density measurement

Antigen density measurement enables researchers to quantify how much of a target is expressed on the surface of individual cells, providing valuable insights for cell therapy, immuno-oncology, biomarker development, and biopharmaceutical research. In a typical quantitative flow cytometry workflow, cells are stained with a biotinylated antibody and detected using Streptavidin-RPE. Fluorescence intensity can then be compared to calibration standards to calculate metrics such as MESF, ABC, or estimated receptor molecules per cell. The exceptional brightness of R-PE supports accurate measurement across a wide range of expression levels, making antigen density analysis a rapidly growing application for flow cytometry.

Receptor occupancy and target engagement

Receptor occupancy assays measure the proportion of receptors engaged by a therapeutic molecule, providing a direct assessment of target engagement and pharmacodynamic activity. These assays typically compare receptor populations before and after treatment using biotinylated probes that detect free receptor, bound receptor, or total receptor levels. Streptavidin-RPE enables sensitive fluorescent detection of these populations, including situations where free receptor levels are low following dosing. As target engagement strategies become increasingly important in drug development, receptor occupancy analysis continues to be a key application for quantitative flow cytometry.