Diamond based electrochemical sensor heads

A diamond electrochemical sensor head comprises a planar sensing surface, a rear surface through which electrical connections are provided, one or more boron doped diamond (BDD) electrodes disposed within trenches in an electrically insulating diamond support matrix at the sensing surface, the electrodes extending partially through the support matrix from the planar sensing surface towards the rear surface of the support matrix, one or more vias extending from the rear surface of the support matrix to a rear surface of the BDD electrodes, one or more ohmic contacts on the rear surface of the BDD electrodes within the vias in the support matrix, and one or more electrical connectors extending through the vias to the ohmic contacts; wherein the sensor head has a thickness in a range 50 micrometres to 1.5mm, the BDD electrodes extend through support matrix from the planar sensing surface towards the rear surface of the support matrix with a depth in a range 20 micrometres to 500 micrometres, and wherein the ohmic contacts each have a resistance which is sufficiently low that an ohmic drop in a faradaic electrochemical experiment is no greater than 10 mV.