Electrophoretic sensitivity control applied on microscale NOx− biosensors with different membrane permeabilities

The entry of ions into biosensors equipped with porous membranes can be enhanced or lowered by migration in an electrical field. We here report how this so called Electrophoretic Sensitivity Control (ESC) technique operates with microscale NOx− (i.e., NO2− + NO3−) biosensors constructed with more and less permeable membranes when exposed to waters of different salinity. The sensors were calibrated at ESC potentials of −0.2 to +0.6 V and at salinities of 0.1, 5 and 35 g NaCl L−1. Our data show that decreasing the membrane permeability allows for a higher ESC response and therefore for a better scaling of the sensor sensitivity. An ESC polarization of +0.2 V was enough to fully compensate for the initial loss in NO3− sensitivity due to the reduced permeability in the less permeable membrane as compared to a highly permeable membrane with no ESC circuit applied at salinities of 0.1 and 5 g L−1. At 35 g L−1 the compensation occurred at +0.4 V, but only for sensors with a thin membrane. In addition to increased possibility of scaling the response of the biosensor, a reduction in permeability allowed for rapid in situ zero-calibration of the sensor and also in more robust membranes with increased adhesion.