Scaffolding Carbon Nanotubes into Single-Molecule Circuitry
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1018-EE08-07
Scaffolding Carbon Nanotubes into Single-Molecule Circuitry Brett R. Goldsmith1, John G. Coroneus2, Gregory A. Weiss2,3, and Philip G. Collins1 1 Dept. of Physics and Astronomy, University of California, Irvine, Irvine, CA, 92697 2 Dept. of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697 3 Dept. of Chemistry, University of California, Irvine, Irvine, CA, 92697 ABSTRACT While nanowires and nanotubes have been shown to be electrically sensitive to various chemicals, not enough is known about the underlying mechanisms to control or tailor this sensitivity. By limiting the chemically sensitive region of a nanostructure to a single binding site, single molecule precision can be obtained in order to study the chemoresistive response. We have developed techniques using single-walled-carbon-nanotube (SWCNT) circuits that enable single-site experimentation and illuminate the dynamics of chemical interactions. Discrete changes in the circuit conductance reveal chemical processes happening in real-time and allow SWCNT sidewalls to be deterministically broken, reformed, and conjugated to target species. INTRODUCTION Chemical, biological, and even mechanical sensor prototypes are all currently explored as possible applications for carbon nanotube (CNT) devices (1). In each case, researchers attempt to exploit the exquisite sensitivity of carbon nanotubes while directing this sensitivity towards a particular target. Because pristine CNTs and as-fabricated devices have cross sensitivities to a wide range of adsorbates including air and water, control over selectivity is a critical research problem. CNT functionalization techniques, in which sensitizing groups are added to a CNT, provide promising solutions to both enhancing sensitivity and directing selectivity. Both noncovalent coatings and covalent sidewall modifications have been used to engineer the electronic properties and environmental sensitivities of CNTs, at least in bulk or on films of networked CNTs (2). While additions of chemical groups along a CNT certainly do lead to sensitivity enhancements, they also result in an ensemble measurement of the environment and do not take advantage of a CNTÃs dimensionality. In principle, the response of a 1-D system may be dominated by a single scattering site (3). In this limit, a CNT circuit can be used to directly transduce single-molecule interactions such as recognition and docking with useful dynamic information. Fig. 1 depicts the two architectures and the type of electronic signals which might be obtained from them. The ensemble device (Fig. 1A) may be advantageous as a commercial sensor demanding calibrated concentration dependence. The single-site sensor (Fig. 1B) is a more useful tool for understanding the transduction mechanism and for studying single-molecule chemistry, and it can be further parallelized to provide the same reliability and calibration as the ensemble device. Here we describe the fabrication and testing of the single-site CNT architecture and provide
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