Cy3.5 BCN

Cy3.5 BCN is a bioorthogonally clickable derivative of Cy3.5, a widely used orange-red fluorescent dye for labeling biomolecules such as peptides and oligonucleotides. Cy3.5 is characterized by strong fluorescence intensity, high photostability, and pH-independent emission across a broad range (pH 4-10).To improve conjugation performance, Cy3.5-BCN incorporates a PEG spacer, which reduces steric hindrance and minimizes potential interference with target binding sites. This design maximizes conjugation efficiency while preserving the biological activity of the resulting conjugate. The bicyclononyne (BCN) moiety enables strain-promoted azide-alkyne cycloaddition (SPAAC) with azido groups, forming stable triazole linkages under catalyst-free conditions. In addition, unlike dibenzocyclooctyne (DBCO), BCN also reacts efficiently with tetrazines through an inverse electron-demand Diels-Alder (IEDDA) reaction. This reaction is rapid, selective, and bioorthogonal, allowing labeling of biomolecules under physiological conditions without the need for metal catalysts or disruption of native biological processes.