Effects of Measurements Conditions on an Extended-Gate FET used as pH sensor

Fluorine-doped tin oxide (SnO₂:F) was investigate as the sensitive part of a pH sensor in the extended-gate field effect transistors (EGFET) device, which provided a linear response for pH range from 2 to 12; the sensitivity was 37 mV.pH^-1 for experiments performed in absence of light. Neutral pH, leads to a transistor’s electric current remained practically constant, suggesting that pH 7 correspond to the isoelectric point of the SnO₂:F samples. For acid and alkaline pH, the power law varied along time and stabilized at about 10 min. UV-vis light did not alter the results. The transistor’s electric current increased with the operating temperature increases. Once that small change in the operating conditions can alter the results, the physical mechanisms underlying the sensing process must be clearly understood. It is essential to monitor transient response and measurements conditions.

Keywords:
Extended-gate FET; Fluorine-doped tin oxide; pH sensor; Temperature dependence; Time evolution