A pH sensor for a single-use container includes a plunger sleeve configured to couple to a flange of the single-use container. A plunger is axially movable within the plunger sleeve between a storage position and an operating position. A pH sensing element coupled to the plunger wherein the pH element is disposed within a storage chamber in the storage position and is configured to be exposed to an interior of the single-use container in the operating position. In one example, a temperature sensitive element is disposed within the pH sensor and configured to sense temperature proximate the pH sensing element. In another example, a lock member is coupled to the plunger, where the lock member has a locked position and an unlocked position, the lock member being configured to inhibit movement of the plunger when in the locked position. In yet another example, the plunger includes at least one filling channel that allows access to a reference fill chamber when the plunger is in a filling position.