Investigation of DNA Decorated Carbon Nanotube Chemical Sensors

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0963-Q21-04

Investigation of DNA Decorated Carbon Nanotube Chemical Sensors M. Chen1, S. M. Khamis2, R. R. Johnson2, C. Staii2, M. L. Klein3, J. E. Fischer1, and A. T. Johnson2 1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, 19104 2 Physics, University of Pennsylvania, Philadelphia, PA, 19104 3 Chemistry, University of Pennsylvania, Philadelphia, PA, 19104 ABSTRACT We demonstrate a versatile class of nanoscale sensors based on single-stranded DNA (ssDNA) as the chemical recognition site and single-walled carbon nanotube field effect transistors (SWNT-FETs) as the electronic readout component. Coating SWNT-FETs with ssDNA causes a current change when exposed to gaseous analytes, whereas bare SWNT-FETs show no detectable change. Sensor responses differ in sign and magnitude depending both on the type of gaseous analyte and the sequence of ssDNA. Our results suggest that the conformation of ssDNA on SWNT-FET plays a role in determining the sensor response to gaseous analytes. The conformation depends not only on the base content of the oligomer, but also on the specific arrangement of the bases in the ssDNA. We compare our results with the molecular dynamic simulation for understanding of the sensing mechanisms. SsDNA/SWNTFETs possess rapid recovery and self-regenerating ability, which could lead to realization of large arrays for sensitive electronic olfaction and disease diagnosis.

INTRODUCTION Semiconducting single-walled carbon nanotubes (SWNTs) have electronic states that lie on the one-dimensional carbon cage structure, making them exceedingly sensitive to environmental stimuli. Bare and polymer-coated SWNTs are found to be sensitive to various gases [1-6]. However, SWNT functionalized with biomolecular complexes [7-11] could detect species that otherwise would have only weak interaction with unmodified nanotubes. These derivatized SWNTs and semiconducting nanowires [12-14] are attractive chemical and molecular sensors due to their high sensitivity, fast response time, and compatibility with array fabrication [15]. Nucleic acid biopolymersí affinity to analytes can be specifically engineered [16,17]. For example, high throughput screening is used to select films of dye-labeled ssDNA for use as gas sensors with fluorescent readout [18,19]. SsDNA has high affinity to SWNT due to an attractive π−π stacking interaction [20]. Such interaction preserves the electronic integrity of the SWNT. These facts motivate the exploration of ssDNA-SWNT hybrid nanostructures as electronic gas sensors.

EXPERIMENT DETAILS SWNTs are grown on SiO2/Si substrate (oxide thickness ~ 200-400 nm) by chemical vapor deposition using an iron salt catalyst. Field effect transistors (FETs) are fabricated by writing source-drain contacts to the nanotubes using electron beam lithography followed by thermal evaporation of chrome and gold. The degenerately doped silicon substrate is used as the backgate. Source-drain current I is measured as a function of gate voltage. Only devices with individual p-type semicon