In a SPR experiment with Biacore T200, I'd like to immobilize my amine-functionalized ssDNA ligands (around 80mer) on the CM5 chip. Although I changed pH , I couldn't immobilize the ligands on the chip well in my first try. I used phosphate buffer (6.5-8) for immobilization. I sincerely appreciate it if you give me your knowledge for this kind of matter.