PH-sensor for determining and/or measuring a pH-value of a medium

A pH-sensor for determining and/or monitoring a pH value of a medium, having:

• a sensor unit with a wall, wherein the wall is in contact with the medium,
• at least one pH-sensitive material, which has at least one spin state that changes as a function of a pH value, wherein the at least one pH-sensitive material is arranged in or on a region of the wall in such a way that the at least one spin state is subjected to a change in the pH value of the medium,
• a spin-sensitive unit, which is configured to detect a variable associated with the at least one spin state, wherein the spin-sensitive unit is arranged in an environment of the at least one pH-sensitive material in such a way that the spin-sensitive unit is subjected to a change in the spin state of the at least one pH-sensitive material, and
• an evaluation unit which, based upon the variable detected by the spin-sensitive unit and associated with the at least one spin state, determines the pH value of the medium.