A system includes a sensor including a sensor pad and includes a well wall structure defining a well operatively connected to the sensor pad. The sensor pad is associated with a lower surface of the well. The well wall structure defines an upper surface and a wall surface extending between the upper surface and the lower surface. The upper surface is defined by an upper buffer material having an intrinsic buffer capacity of at least 2×1017 groups/m2. The wall surface is defined by a wall material having an intrinsic buffer capacity of not greater than 1.7×1017 groups/m2.