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Carbon nanotubes (CNTs) field effect transistor (FET) sensor has been investigated after the first fabrication of CNT-FET device on silicon oxide substrate by Tans et al. We fabricated CNT-FET on a glass substrate by controlled immobilization of commercial single wall CNTs. The CNTs are washed by a mixture of acids and hydrogen peroxide, and it forms a rope of CNTs after dialysis against pure water to obtain CNTs aqueous solution. N-(5-Amino-1-carboxypentyl)iminodiacetic acid(NTA) was immobilized on the surface of the CNT ropes by amide bond. The NTA modified CNT (NTA-CNT) is easy to aggregate in the presence of Ni cations. The aggregation of NTA-CNT can be controlled by changing pH or ionic strength in the absence of the Ni cations. On the glass substrate, the source and drain electrodes areas are developed by photolithography and then the areas are modified by a sol-gel structure of 3-aminoproplytriethoxysilan. After removing the photoresist, the NTA-CNT aqueous solution is dropped on the area in metal cations free condition. The ropes of the NTA-CNTs are specifically immobilized on the sol-gel structure on the electrode areas and some of the NTA-CNTs could be immobilized between the sources and drain electrodes area. Cr/Au layers were deposited on the electrode area to cover the sol-gel structures. We measured current through the electrodes (Ids) when a gate potential was applied in the range from –700 to –200 mV using Ag/AgCl electrode after dropping a buffer on the CNTs. The Ids-Vgate curves of the NTA-CNT device showed typical p-type FET properties. The droplets of various pH buffers were dropped on the CNT ropes. The Ids-Vgate shifted to positive or negative after dropping various pH solutions with a high reproducibility. After addition of Ni cation, Ids-Vgate curves shifted to negative due to the neutralization of negatively charges of carboxylic acids of NTA by the Ni cations. However, the pH dependency was still remained. In the case of unmodified CNT, Ids-Vgate curves slightly shift to negative by addition of the Ni cations. These results indicated that the NTA-CNT-FET could detect the binding of Ni cation to NTA molecule on CNT . We will discuss the application of the NTA-CNT-FET device for a biosensor. |