Sensor apparatus

A sensor apparatus, comprising:

• an element substrate;
• a detecting section disposed on and in direct contact with an upper surface of the element substrate, the detecting section comprising a reaction section having an immobilization film to detect an object to be detected, a first IDT electrode configured to generate an acoustic wave which propagates toward the reaction section, and a second IDT electrode configured to receive the acoustic wave which has passed through the reaction section, wherein the first and second IDT electrodes are located on the upper surface of the element substrate;
• and
• a protective film located on the upper surface of the element substrate so as to cover the first IDT electrode, the second IDT electrode, and a first part of the immobilization film, wherein a second part of the immobilization film is not covered by the protective film, the protective film extending between and contacting the immobilization film and at least one of the first IDT electrode and the second IDT electrode, and wherein, in an upper surface of the immobilization film, a region covered with the protective film is at a higher level than a region which is not covered with the protective film.