There are two strategy for DNA probe immobilization on iron ferum oxide nanoparticles. First step is SAM interaction where u can treated your nanoparticles with APTMS or APTES through silanization process to introduce Amines Group. Then, this amines modified electrode is modify with glutaradehyde solution. With activation of EDC/NHC, u can easily immobilize your probe DNA. Second step, is electrostatic interaction. Same procedure above when your nanoparticle treated with aptms, aptes. Since Amine group is positive charge and DNA has negative charge phosphate bond, it can bind each other. I hope I can answer your question.

Thank you for your answer. I am now trying to use avidin-biotin binding strategy.