The acid-base properties of carboxylated CNT and the design of CNT based biosensor

We observed the sign of the two responses from carboxylated carbon nanotube (CNT) based sensor in aqueous solution by means of dynamic measurements. Two types of surface groups, the hydroxyl and the carboxyl group of sensor surface are amphoteric materials depending on the pH. The protonation/deprotonation of these surface groups modulates CNT conductance. After blocking of COOH group on the CNT surface, CNT characteristics become insensitive to pH condition. This result brings benefits to reliable operation and high sensitivity of CNT based sensor.