Field effect transistors (FETs) modified with various functional monolayers, such as organosilane monolayer, were formed on the identical substrate by precise control of the fabrication processes. The devices showed a typical transistor property with a good stability in aqueous solutions. The amino monolayer-modified FET acted as an ion sensitive FET with a good pH sensitivity of 58 mV/pH, and the perfluoro-alkyl monolayer-modified FET worked as a reference device. Moreover, the device with enzyme immobilized onto amino modified gate electrode enabled to detect trace concentration (10-9 to 10-6 M) of urea with a high sensitivity of 64 mV/decade. These monolayer-modified devices were expected to be applied as working and reference electrodes for on-chip ion and biosensing.
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