N-(azide-PEG3)-N'-(PEG4-NHS ester)-Cy5

N-(azide-PEG3)-N'-(PEG4-NHS ester)-Cy5 is a Cy5-based bioconjugation reagent that combines a terminal azide handle with an NHS ester for amine-reactive labeling. The PEG spacers support conjugation flexibility and help reduce steric constraints when building fluorescent conjugates for imaging and fluorescence-based assays, where Cy5 excitation/emission enables far-red detection with common fluorescence microscope and plate reader setups.

1. Protein Amine Labeling

N-(azide-PEG3)-N'-(PEG4-NHS ester)-Cy5 is used to fluorescently tag proteins through the NHS ester, generating Cy5-labeled biomolecules that retain a remaining azide functional group for downstream click chemistry. Researchers commonly employ this reagent to prepare antibody conjugates, enzyme conjugates, and protein standards for fluorescence microscopy and quantitative fluorescence measurements, especially when a two-step workflow is preferred (first install the Cy5 label, then couple to a second partner via azide-reactive click chemistry). The PEG4-NHS ester portion enables efficient coupling to accessible lysine residues or N-termini under typical bioconjugation conditions, while the PEG3 spacer helps maintain labeling accessibility for subsequent conjugation steps.

2. Two-Step Click Conjugation

N-(azide-PEG3)-N'-(PEG4-NHS ester)-Cy5 supports modular construction of fluorescent probes and multicomponent bioconjugates by separating the initial Cy5 installation from the final assembly step. After Cy5 attachment to an amine-bearing target, the terminal azide can be used as the click handle to connect the labeled biomolecule to complementary alkyne-functional partners, such as targeting ligands, affinity handles, or imaging scaffolds. This workflow is widely used in chemical biology for preparing fluorescent tracking reagents, multivalent binding constructs, and conjugates where controlling the order of labeling and coupling reduces cross-reactivity and improves reproducibility in probe development.

3. Surface and Material Functionalization

N-(azide-PEG3)-N'-(PEG4-NHS ester)-Cy5 is applied in biomaterials and surface engineering workflows to introduce Cy5 fluorescence onto amine-containing coatings and functional layers prior to immobilization or further click-based patterning. Laboratories often use the NHS ester chemistry to incorporate the dye into protein-coated surfaces, polymer matrices, or other amine-functional substrates, then leverage the azide group for subsequent attachment to alkyne-functional surfaces or capture elements. The PEG spacers help improve accessibility of both the dye and the reactive handle, supporting consistent fluorescent readouts in imaging experiments and enabling fabrication of fluorescently addressable materials for microscopy and fluorescence-based characterization.

4. Fluorescent Imaging Probes

N-(azide-PEG3)-N'-(PEG4-NHS ester)-Cy5 is used as a building block for developing far-red fluorescent imaging reagents where Cy5 brightness and spectral separation are advantageous. In microscopy and fluorescence assay development, teams commonly label biomolecular targeting components with the NHS ester to generate Cy5-tagged intermediates, then use the azide handle to assemble final probes with defined stoichiometry or multivalent architectures. This approach is particularly useful when probe construction requires orthogonal functional groups, allowing researchers to tune labeling density and coupling order while maintaining a robust fluorescence signal for cellular imaging, binding studies, or fluorescence readouts in assay formats.