A sensing cell includes: a first electrode coupled to the gate electrode of a transistor, and a second electrode spaced apart from the first electrode; a protective layer covering sidewalls of the first electrode and the second electrode and having a first opening and a second opening, exposing a first part of the first electrode and second part of the second electrode, respectively; a first well on the protective layer, surrounding the first electrode and the second electrode, and having a third opening exposing a first part of the first electrode, a second part of the second electrode, and the protective layer between the first opening and the second opening; the second well located on the protective layer, surrounding the first well and having a fourth opening to limit the flow of a liquid to be tested; and an ion selective membrane, located in the third opening. |