Effects of buffer concentration on sensing performances of ion-sensitive field-effect transistors wth si-nanowires

We have experimentally investigated the effect of buffer-dilution on sensing characteristics of the Si-nanowire (Si-NW) ion-sensitive field-effect transistors (ISFETs). Phosphate-buffered saline (PBS) with various buffer concentrations was prepared. The result showed that the sensitivity increases as the buffer concentration decreases for bio-molecule detection, while the pH sensitivity of the Si-NW FETs is insensitive to the buffer solutions. The Debye length of the buffer solution can be a crucial factor to detect biomolecules using FET sensors. For the buffer solution with high ionic strength, the Debye length becomes shorter than the distance between the sensing membrane and the target-molecules so that the charges of target-molecules are screened out. For the pH sensing, however, small hydrogen ions can be bound close to the channel surface and thus little dependence on the buffer concentration.