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In this paper, we present a suspended Single-Walled Carbon Nanotube (SWNT) based pH sensor utilizing a low temperature Dielectrophoretic (DEP) assembly process on a flexible parylene-C substrate. Parylene-C, a light weight, flexible and inert material, is compatible with many microfabrication processes. Furthermore, utilizing parylene-C as a flexible substrate, one can readily create a suspended microplatform utilizing an O2 plasma etch process. Suspended nanobridges have larger exposed surface areas and may potentially have enhanced sensitivity for sensing applications. Fabricating these structures on a thin (10 microm) parylene-C substrate allows their utilization as flexible devices or in wearable sensor applications. We have successfully assembled suspended SWNT nanobridges across a spacing of 4 microm. The electrical characterization results from the assembled SWNTs yield ohmic behavior with a measured two-terminal resistance of approximately 17Komega. Furthermore, the conductometric measurements of the SWNT sensors have demonstrated that corresponding to an increase in pH value, the resistance of SWNTs has decreased due to the OH- group that attached on to the wall of the SWNTs and changed the electrical properties of the SWNTs. These novel suspended nanostructures can be used as potential candidates in nanosensor applications.

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Single-Walled Carbon Nanotubes (SWNTs) are reported to be very sensitive to numerous odors and could serve as the next generation of miniature gas sensors. Recently, we have shown that SWNTs functionalized with DNA hold even greater promise than bare SWNTs as high sensitivity gas sensors. The DNA-decorated SWNT gas sensors were integrated on CMOS circuitry with built-in amplifiers. In the paper, we report on the performance of the nanosensors as a function of the DNA sequence used for adsorption on SWNTs. A diverse sequence-dependent response was observed, with enhancements up to 300% for methanol vapor and 250% for isopropanol alcohol vapor for specific DNA sequence compared to bare SWNTs. This work demonstrates a significant step towards ultra-sensitive electronic nose type of applications based on functionalizing CNTs with different DNA sequences.

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