Silicon nanowires as pH sensor

Silicon nanowires (SiNWs) have been used as a sensing layer in an extended-gate field-effect transistor (EGFET) for the measurement of solution pH. SiNWs were synthesized directly from silicon substrates via a catalytic reaction in N-2 atmosphere at 955 degrees C. The SiNWs have an average diameter of approximately 30-50 nm and a length of up to a few tens of micrometers. Here, silicon bulk materials and SiNWs were used alternately as the sensing layer in an extended-gate field-effect transistor in measuring solution pH. Experimental results showed that the pH sensitivity of silicon bulk materials is poor. However, good pH sensing properties of SiNWs, with a sensitivity of 58.3 mV/pH, was observed. Therefore, it was suggested that the pH sensitivity of silicon bulk materials was greatly improved by downsizing them to the nanoscale.