Figure 3. A spearhead nano-FET made by deposition of polypyrrole to comprise the channel (a) works as a highly sensitive pH biosensor. From I–VG curves (b) changes in pH value can be measured as change of average drain–source current or drain–source peak currents (c) as well as shift in gate voltage (d). The pH-sensitive PPy nano-FET is applied to measure the local pH in the microenvironment of cell samples (e). Prior to cell measurements the PPy nano-FET is calibrated with physiological pH variations from 5 to 7.5 (f). Local pH measurements by alternating vertical approach and withdrawal of the PPy nano-FET probe to breast cancer tissue (g), a cluster of melanoma cells (h), and a single melanoma cell (i).
