Study of field effect transistors for the sodium ion detection using fluoropolysiloxane-based sensitive layers

A membrane for the development of Na+ sodium ion sensitive field effect transistor (pNa-ISFET) is described in this work. This membrane is based on a fluoropolysiloxane (FPSX) polymer modified by sodium ionophore. The advantages of using such polymer are several: it permits good adhesion properties on silicon-based layers, it is characterized by a lower resistivity and it is fully compatible with ink jet printing technique. Thus, FPSX membranes were developed in the frame of a pH-ChemFET/Ag/AgCl reference electrode industrial fabrication process. Studies involve the deposition of FPSX-based, sodium ion sensitive layers by ink jet printing, the integration and characterization of Ag/AgCl reference electrode, as well as the pNa measurement in solution. Thus, whatever the reference electrode used, FPSX-based pNa-ISFET microsensors show good detection properties with sensitivity around 57 mV/pNa, detection limit around 10−4 M, low pH interferences (7 mV/pH in the [9–12] basic range) and selectivity coefficient versus potassium K+ ion-3. Final application is done through analysis of real sweat samples.