Functionalized Carbon Nanotube Thin Films as the pH Sensing Membranes of Extended-Gate Field-Effect Transistors on the Flexible Substrates

The oxygen-plasma-functionalized carbon nanotube thin films on the flexible substrates as the pH sensing membranes of extended-gate field-effect transistors are proposed for the first time. The carbon nanotubes are ultrasonically sprayed onto the polyimide substrates followed by an oxygen-plasma functionalization. Such oxygen-plasma-treated carbon nanotube thin films (CNTFs) exhibit superior pH sensing characteristics with the sensitivity of 55.7 mV/pH and voltage linearity of 0.9996 in a wide sensing range of pH 1-13. Moreover, the excellent flexibility of carbon nanotube is also demonstrated and the oxygen-plasma-treated CNTFs still maintain the sensitivity of 53.6 mV/pH and voltage linearity of 0.9943 even after five-cycle bending test. These results reveal that the oxygen-plasma-treated CNTFs have great potentials in the practically disposal and wearable biosensor applications.