Cy2-SE (iodine) is a Cy2 derivative with excitation/emission wavelengths of 475/510 nm. Cy2 is an amine-reactive fluorophore commonly employed for fluorescent labelling of proteins and nucleic acids.

Reference for the usage of Cy2-SE (iodine):
1. Protein Preparation
It is recommended to prepare the protein (antibody) solution at a concentration of 2 mg/mL, with a pH of 8.5 ± 0.5. If the pH is below 8.0, adjust it using 1 M sodium bicarbonate.
Note: If the protein concentration is below 2 mg/mL, the labeling efficiency will significantly decrease. For optimal labeling efficiency, the recommended final protein concentration range is 2–10 mg/mL. The protein buffer must not contain primary amines (e.g., Tris or glycine) or ammonium ions, as these will affect labeling efficiency.
2. Dye Preparation
Dissolve Cy2-SE (iodine) dye in anhydrous DMSO to prepare a 10 mg/mL stock solution—Aliquot and store at -20°C or -80°C, protected from light.
3. Dye Quantity Calculation
The required amount of Cy2-SE (iodine) dye for the labeling reaction depends on the quantity of protein to be labeled. The optimal molar ratio of Cy2-SE (iodine) dye to protein is approximately 10.
Example: If the protein to be labeled is 500 μL of 2 mg/mL IgG (MW = 150,000), dissolve 1 mg of Cy2-SE (iodine) dye in 100 μL DMSO. The required volume of Cy2-SE (iodine) is 4.31 μL, calculated as follows:
1) mmol (IgG) = mg/mL (IgG) × mL (IgG) / MW (IgG) = 2 mg/mL × 0.5 mL / 150,000 mg/mmol = 6.7 × 10⁻⁶ mmol
2) mmol (Cy2-SE (iodine)) = mmol (IgG) × 10 = 6.7 × 10⁻⁶ mmol × 10 = 6.7 × 10⁻⁵ mmol
3) μL (Cy2-SE (iodine)) = mmol (Cy2-SE (iodine)) × MW (Cy2-SE (iodine)) / mg/μL (Cy2-SE (iodine)) = 6.7 × 10⁻⁵ mmol × 643.47 mg/mmol / 0.01 mg/μL = 4.31 μL (Cy2-SE (iodine))
4. Labeling Reaction
Slowly add the corresponding volume of 10 mg/mL Cy2-SE (iodine) dye to 0.5 mL of the protein sample solution. Mix gently, then briefly centrifuge to collect the sample at the bottom of the reaction tube. Incubate the reaction tube in the dark at room temperature with gentle shaking for 60 minutes, inverting the tube several times every 10–15 minutes.
5. Protein Purification
Purify the dye-protein conjugate using an appropriate method.