Fluorescein-PEG4-acid | CAS 1807518-76-8

Fluorescein-PEG4-acid is a fluorescein-based fluorescent dye featuring a short polyethylene glycol spacer that improves aqueous handling and reduces nonspecific interactions relative to more hydrophobic fluorescein derivatives. The carboxylic acid functionality enables straightforward incorporation into labeling workflows where dye conjugates are prepared for fluorescence microscopy, flow cytometry, and fluorescence-based assays. Its bright, green-emitting fluorescence makes it a common choice for constructing fluorescent conjugates and tracking biomolecular or material-associated processes in chemical biology and biomaterials research.

1. Protein And Peptide Labeling

Fluorescein-PEG4-acid is frequently used as a fluorescent tag precursor for preparing fluorescein-labeled proteins and peptides for binding and localization studies. Researchers in chemical biology and medicinal chemistry use fluorescein conjugates to visualize conjugate distribution in assay formats such as microplate fluorescence readouts and imaging experiments, where the PEG spacer helps maintain solubility and can moderate dye-biomolecule crowding effects. The dye's carboxylic acid handle is leveraged in conjugate construction strategies to generate stable fluorescent labeling reagents for downstream experiments involving purified targets, affinity reagents, or biomolecule tracking.

2. Fluorescence Microscopy Tracing

Fluorescein-PEG4-acid supports fluorescence microscopy workflows where green fluorescence is used to trace labeled biomolecules in cells, extracellular matrices, and biomaterial environments. In practice, teams performing cellular imaging and materials characterization incorporate fluorescein-containing conjugates to monitor uptake, diffusion, and surface-associated retention in experimental systems where a hydrophilic spacer is helpful for reducing background staining from dye aggregation. The dye's compatibility with common fluorescence microscope filter sets and its strong emission behavior make it a practical choice for routine imaging-based studies that require a robust green channel reporter.

3. Flow Cytometry Fluorescent Labeling

Fluorescein-PEG4-acid is used to prepare fluorescein-based staining reagents for flow cytometry experiments that quantify fluorescence intensity on labeled cells or biomolecular complexes. In typical workflows, researchers generate fluorescein conjugates that report on binding to cell-surface features, labeling of biomolecules associated with cell populations, or tracking of tagged reagents during incubation-based assays. The PEG4 spacer contributes to improved aqueous behavior during staining and washing steps, supporting more consistent signal generation when comparing fluorescence across samples.

4. Fluorescence Bioassay Development

Fluorescein-PEG4-acid is also applied in fluorescence assay development as a dye component for constructing labeled substrates, tracers, or readout reagents used in screening and mechanistic studies. Bioconjugation teams incorporate fluorescein into assay reagents to enable real-time or endpoint fluorescence measurements in plate-based formats, including binding/competition assays and reagent tracking assays where a green-emitting reporter is convenient. The carboxylic acid functionality supports reagent design for conjugate preparation, while the PEG spacer helps maintain dye performance in aqueous assay buffers where nonspecific interactions can otherwise contribute to background.