There are three ways to immobilize a protein on a Surface Plasmon Resonance (SPR) or Quartz Crystal Microbalance (QCM) biosensor consisting of Self-Assembled Monolayer (SAM). 1) Formation of covalent bond of amine functions on proteins and activated carboxy-SAM 2) immobilize proteins by His-Tag through Ni-NTA-terminated SAM 3) Immobilization of proteins through Biotin and Avidin interaction. The Biotin-Avidin formation is known as a facile reaction, thus it is widely utilized for immobilization of protein. Dojindo has various reagents for biosensor research. (https://www.dojindo.com/surface-chemistry/)