Novel asymmetric Cy5 dyes: Synthesis, photostabilities and high sensitivity in protein fluorescence labeling

Several novel water-soluble asymmetric pentamethine cyanine dyes were synthesized. The maximum absorption and emission wavelengths of the dyes in different solvents were in the range from 647 to 665 nm and exhibited negative solvatochromism with increasing solvent polarity. The fluorescence quantum yields of the dyes were about 0.1 in water, and were obviously higher than those of hydrophobic cyanine dyes. Dyes with N-benzyl groups and N-sulfo-groups displayed greater photostability than dyes with N-carboxypentyl groups in water. The limit of detection of dye 5a for BSA was 1.2 × 10−8 mol L−1 by high performance liquid chromatography with fluorescent director about 100-fold lower than that by UV detection (1.0 × 10−6 mol L−1). Therefore, Dye 5a could be used to improve photostability and detection sensitivity in protein analysis.