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The bare carbon nanotube (CNT) was applied for the channel to detect the large size antigen of IgE as shown in Fig. 1. The aptamer, which is a single strand DNA and selectively reacts with IgE, was immobilized on CNT using linker. As the size of aptamer is as small as 1~2 nm, the reaction of aptamer with IgE occurred within the Debye length. Therefore, the electrical charge of IgE could be detected as the change of the CNT channel conductance. Using this method, IgE of as small as 250 pM could be detected as shown in Fig. 2. Another approach of the biosensor is to use CNT as a working electrode for the electrochemical reaction as shown in Fig. 3. As CNT electrode has a far larger surface area compared to the conventional planar type electrode such as a Pt electrode, the oxidized current of the biomolecule at the working electrode increased in proportional to the surface area size, which means the increase of the sensitivity. For the detection of the PSA (Prostate Specific Antigen), the surface of the CNT is modified by the anti-PSA using the linker. When the PSA/a-PSA reaction occurs, the oxidized current of the PSA/a-PSA molecule is few times larger than that of a-PSA only as shown in Fig. 3. The lowest PSA
concentration of 0.5 ng/mL could be detected. 　When the input signal is too small to detect, noise power is added to the input signal to CNT FET which is under the threshold condition. Then, the input signal could reach the threshold of CNT FET and it becomes on state and detects the input signal. This is referred to as stochastic resonance phenomena, which we have succeeded in observing using the CNT FET as shown in Fig. 4. By increasing the number of the channel, the correlation factor between the output/input becomes increased. For this purpose, CNT multi channel FET was realized using the direction controlled growth on the patterned SiO2/Si substrate. The stochastic resonance phenomena could be applicable for the biosensing in the large noise circumstances. Graphene is surface sensitive material and can be applicable to the biosensor. We have first succeeded in detecting the different concentrations of BSA as the shifts of the Dirac point of the graphene FET as shown in Fig. 5, which are linearly proportional to the BSA concentration. As small as 300 pM BSA could be detected. Carbon based biosensors showed the superior characteristics compared to the conventional biosensors because of the high FET characteristics and large surface area and will be applicable in the real world in near future.