We used covalent attachments to single-walled carbon nanotubes (SWNTs) to fabricate single-molecule electronic devices. The technique does not rely on submicrometer lithography or precision mechanical manipulation, but instead uses circuit conductance to monitor and control covalent attachment to an electrically connected SWNT. Discrete changes in the circuit conductance revealed chemical processes happening in real time and allowed the SWNT sidewalls to be deterministically broken, reformed, and conjugated to target species. By controlling the chemistry through electronically controlled electrochemical potentials, we were able to achieve single chemical attachments. We routinely functionalized pristine, defect-free SWNTs at one, two, or more sites and demonstrated three-terminal devices in which a single attachment controls the electronic response.

Observing Protein Dynamics: Following the dynamics of protein conformational changes over the relatively long periods of time typical of enzyme kinetics can be challenging. Choi et al. (p. 319 ; see the Perspective by Lu ) were able to observe changes in lysozyme conformation, which changes its electrostatic potential, by using a carbon-nanotube field-effect transistor. Slower hydrolysis steps were compared with faster, but unproductive, hinge motion, and changes in lysozyme activity that occur with pH were shown to arise from differences in the relative amount of time spent in processive versus nonprocessive states.

The chemical reactivity of carbon nanotubes in ${\mathrm{H}}_2{\mathrm{SO}}_4$ is investigated using individual, single-walled carbon nanotubes (SWNTs) incorporated into electronic devices. Exploiting the device conductance as a sensitive indicator of chemical reactions, discrete oxidation and reduction events can be clearly observed. During oxidation, a SWNT opens circuits to a nanometer-scale tunnel junction with residual conduction similar to Frenkel-Poole charge emission. When electrochemically reduced, a SWNT returns to its original conductance. This redox cycle can be repeated many times, suggesting a novel chemical method of reversibly switching SWNT conductivity.