An antibody immobilization was investigated using a self-assembled monolayer (SAM) over the highly refractive coatings with a SiO2, TiO2, or Si3N4 substrate. The immobilization was characterized by analyzing the hydrophilic properties of hydroxyl (OH) groups on Surface coatings with contact angle (CA) measurements to enhance protein immobilization. The hydroxyl (OH) group was formed in greater amounts its the oxygen plasma exposure time was increased, which resulted in a large enhancement in antibody immobilization. It indicated that hydroxyl (OH) group formation is critical for developing a label-free optical transducer with a high sensitivity.