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 non-diamond carbon surface groups bonded to the non-diamond carbon sites for generating a first redox peak at a first potential associated with dissolved oxygen and a second redox peak at a second potential which changes with pH, the first and second redox peaks being separated such that they do not overlap, an electrical controller configured to scan the boron doped diamond electrode over a potential range to generate at least said first redox peak, and a processor configured to give an electrochemical reading based on one or both of a position and an intensity of said first redox peak.