An electrochemical sensor comprising: a boron doped diamond electrode formed of boron doped diamond material; an array of non-diamond carbon sites disposed on a sensing surface of the boron doped diamond electrode; electrochemically active surface groups bonded to the non-diamond carbon sites for generating a redox peak associated with a target species which reacts with the electrochemically active surface groups bonded to the non-diamond carbon sites when a solution containing the target species is disposed in contact with the sensing surface in use; an electrical controller configured to scan the boron doped diamond electrode over a potential range to generate said redox peak; and a processor configured to give an electrochemical reading based on one or both of a position and an intensity of said redox peak.