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