1. Change buffer for the protein (or antibody) solution to 0.1 M sodium carbonate.
2. Protein concentration should be 1-2 mg/ml.
3. Prepare fresh N-hydroxysuccinimido-Biotin (NHS-Biotin, 10 mg/ml) in
NHS-Biotin attachs through free amino group, usually lysine residues.
4. For each mg of protein, add 20-100 mg of NHSE.
5. Incubate at room temperature in the dark for 3-4 hours with rotation.
6. Stop reaction by adding 2 ml of NH4Cl
or by change buffer to 10 mM Tris-HCl, 150 mM NaCl, pH7.5-8.0.
7. If adding NH4Cl, an amine-free buffer (e.g., PBS) can
be exchanged into for storage.