CY5-SE (Cy5 NHS Ester) is a reactive dye used to label amino groups in peptides, proteins and nucleotides. It needs to be stored away from light. Excitation wavelength (nm): 640, emission wavelength (nm): 664.

1 mL of each 100 μg/mL SELP solution in 100 mM sodium bicarbonate buffer (pH 8.3) was mixed with 10 μL of 1.2 mg/mL Cy5 mono NHS-ester（CY5-SE） in 10% dimethyl sulfoxide and incubated for 2 h on ice. To quench the reaction, 50 μL of 1 M Tris-HCl (pH 8.0) was added to the reaction solution. To calculate molar concentrations of Cy5 and SELP in the Cy5-conjugated SELPs, reactions containing designated concentrations of pure SELP and BCA solution were conducted for 30 min at 37 °C. The absorbances of SELP and Cy5 at 562 and 633 nm were then obtained using the Microplate reader. [1]