POSSIBLE DEVELOPMENTS OF A POTENTIOMETRIC BIOSENSOR

Since the introduction of the light addressable potentiometric sensor, much work has been done to monitor several chemical and biological specimens, and to theoretically describe the system itself. The device is essentially an oxide/silicon wafer lighted with a modulated LED; an electrolyte is in contact with the oxide. The hole-electron pairs generation yields an a.c. current, measured as a function of bias potential, which depends on the pH of the electrolyte. The output curves are strictly dependent on the device and on the driving system and its parameters, such as frequency and shape of the signals sent to the biosensor. We aim to improve the measuring conditions, namely dopant quantities, chemical treatment and insulator characteristics, in order to allow higher sensitivity. Several modifications to the original device were implemented and experimentally tested: introduction, on the insulator, of an ion-selective membrane, in order to modify the output as a function of the concentration of a particular ion, not necessarily H+; separation of the 'ion-sensitive' part of the device from the silicon wafer, lighted with an IR LED; cells or other biological materials can then be kept in living conditions more easily; new electronics to avoid the use of a lighted wafer.