Sulfo-Cy5 carboxylic acid | CAS 1121756-16-8

Sulfo-Cy5 carboxylic acid is a water-soluble cyanine dye designed for fluorescent labeling workflows where efficient conjugation to biomolecules or materials is required. Its sulfonate substitution supports aqueous compatibility, while the carboxylic acid handle enables amide coupling strategies to generate Cy5-labeled probes for fluorescence imaging and assay development using standard Cy5 excitation/emission detection channels.

1. Protein Conjugation Labeling

Sulfo-Cy5 carboxylic acid is widely used to prepare Cy5-labeled proteins for fluorescence microscopy, fluorescence-based binding studies, and quantitative fluorescence assays. Researchers typically couple the carboxylic acid functionality to primary amine groups on antibodies, affinity reagents, enzymes, or protein scaffolds to generate stable fluorescent conjugates that can be tracked in solution or on surfaces. In bioconjugation workflows, the sulfonate-rich dye format is often selected to maintain dye solubility during labeling, purification, and downstream imaging steps.

2. Fluorescence Microscopy Tracing

Sulfo-Cy5 carboxylic acid supports cellular and biomolecular tracing experiments where Cy5-channel imaging is preferred for multiplexing or reduced background relative to shorter-wavelength fluorophores. After conjugation to targeting ligands, antibodies, or other labeling reagents, the resulting Cy5 fluorescent conjugates are used to visualize localization patterns in fixed-cell imaging, co-localization studies, and multi-color microscopy panels. The dye's strong far-red emission is particularly useful when researchers need clear separation from common green/orange fluorophores in imaging datasets.

3. Flow Cytometry Fluorescent Tagging

Sulfo-Cy5 carboxylic acid is frequently incorporated into fluorescent labeling reagents for flow cytometry and cell-sorting workflows that rely on far-red detection channels. Cy5-labeled antibodies or protein conjugates prepared from this dye are used to quantify binding to cell-surface markers, monitor reagent uptake or association, and support multi-parameter phenotyping panels. The water-soluble sulfonate character helps maintain conjugate handling in aqueous staining buffers, which is important for reproducible labeling and consistent signal readout across experiments.

4. Fluorescent Bioassay Development

Sulfo-Cy5 carboxylic acid is used in fluorescence assay development where Cy5-labeled reagents provide a robust optical reporter for monitoring binding events, reagent interactions, and assay readouts. Conjugates generated from the dye are commonly used as fluorescent tracers in plate-based assays, including format development for binding curves and competition experiments. In these workflows, the carboxylic acid functionality enables coupling to amine-containing assay components, allowing researchers to tailor fluorescent probe density and conjugate composition for their specific assay design.