Enhanced sensitivity of an organic field-effect transistor pH sensor using a fatty acid Langmuir–Blodgett film

An ion-sensitive organic field-effect transistor (ISOFET) has been fabricated by using poly(3-hexylthiophene) as the semiconductor and polymethylmethacrylate as the gate insulator. With the gate metallization replaced by an Ag/AgCl reference electrode, and following suitable encapsulation, the ISOFETs exhibit transistor behavior in an aqueous environment. Moreover, the devices are shown to respond to changes in pH of the solution. A significant increase in the sensitivity of the ISOFET to H+ ions was found by depositing a Langmuir–Blodgett film of arachidic acid on top of the gate insulator.