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We have developed a horizontally aligned carbon nanotube sensor that enables not only the specific detection of biomolecules with ultra-sensitivity, but also the quantitative characterization of binding affinity between biomolecules and/or interaction between a carbon nanotube and a biomolecule, for future applications in early diagnostics. In particular, we have fabricated horizontally aligned carbon nanotubes, which were functionalized with specific aptamers that are able to specifically bind to biomolecules (i.e. thrombin). Our detection system is based on scanning probe microscopy (SPM) imaging for horizontally aligned aptamer-conjugated carbon nanotubes (ACNTs) that specifically react with target biomolecules at an ultra-low concentration. It is shown that the binding affinity between thrombin molecule and ACNT can be quantitatively characterized using SPM imaging. It is also found that the smart carbon nanotube sensor coupled with SPM imaging permits us to achieve the high detection sensitivity even up to $1 pM, which is much higher than that of other bioassay methods. Moreover, we have shown that our method enables a quantitative study on small molecule-mediated inhibition of specific biomolecular interactions. In addition, we have shown that our ACNT-based system allows for the quantitative study of the effect of chemical environment (e.g. pH and ion concentration) on the binding affinity. Our study sheds light on carbon nanotube sensor coupled with SPM imaging, which opens a new avenue to early diagnostics and drug screening with high sensitivity.

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By using DNA linkers, we are able to conjugate self-crosslinked SWNTs which could be detected upon hybridization with a DNA immobilized resonator. The DNA immobilized resonator is able to detect SWNTs with a detection limit of 10 ng ml(-1) which was 2-3 orders of magnitude smaller than the reported SWNT toxicity concentration.

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