The present disclosure relates to a sensor including an elongated member including at least a portion that is electrically conductive. The elongated member includes a sensing layer adapted to react with a material desired to be sensed. An insulating layer surrounds the elongated member. The insulating layer defines at least one access opening for allowing the material desired to be sensed to enter an interior region defined between the elongated member and the insulating layer. The insulating layer has an inner transverse cross-sectional profile that is different from an outer transverse cross-sectional profile of the elongated member. The difference in transverse cross-sectional profiles between the elongated member and the insulating layer provides channels at the interior region defined between the insulating layer and the elongated member. The channels extend generally along the length of the elongated member and are sized to allow the material desired to be sensed to move along the length of the sensor.