We have investigated the electrolyte-solution-gate field effect transisitors (SGFETs) used hydrogen terminated (H-terminated) or partially oxygen terminated (O-terminated) polycrystalline diamond surface in the Cl - and Br- ionic solutions. The H-terminated channel SGFETs are insensitive to pH values in electrolyte solutions. The threshold voltages of the diamond SGFETs shift according to the density of Cl- and Br- ions about 30 mV/decade. One of the attractive biomedical applications for the Cl- sensitive SGFETs is the detection of chloride density in blood or in sweat especially in the case of cystic fibrosis. The sensitivities of Cl- and Br- ions have been lost on the partially O-terminated diamond surface. These phenomena can be explained by the polarity of surface change on the H-terminated and the O-terminated surface.
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