Sensitivity control of ion-selective biosensors by electrophoretically mediated analyte transport

We present a new method for changing the sensitivity of any microsensor that functions by converting an ion into an uncharged molecule which is subsequently detected. The method is based on attraction or repulsion of ions from the sensor tip by an applied potential. We have named the principle electrophoretic sensitivity control (ESC), and it was used to enhance the performance of microscale NO3- biosensors. Applying positive ESC potentials made it possible to increase the sensitivity by a factor of up to 20, whereas negative ESC potentials decrease the sensitivity by a factor of up to 1000. The upper limit for sensitivity enhancement in the tested NO3- biosensors was set by a tendency of bacteria in the sensor tip to be electrophoretically transported away at high positive ESC potentials. The possibility for decreasing the sensitivity by applying negative ESC potentials offers a convenient method for performing a zero check even when the analyte is present. (C) 1999 Elsevier Science B.V. All rights reserved.