Surface-modified Diamond Field-effect Transistors for Enzyme-immobilized Biosensors

The enzyme sensors using electrolyte-solution-gate diamond field effect transistors (SGFETs) have been developed for the first time. The hydrogen-terminated surface channel of the FETs was modified into partially aminated and oxygen-terminated (H-A-O-terminated) with irradiation of ultraviolet in an ammonia environment. The pH response of that is obtained about 50 mV/pH at pH 2–10. The concentration of substrates (urea or glucose) in the electrolyte solution has been detected by the pH change due to the bio-catalyzed effect of enzyme (urease or glucose oxidase), which is immobilized on the channel of SGFETs. The sensitivity of urea and glucose is approximately 30 mV/decade and 20 mV/decade respectively.