Single-Molecule Carbon Nanotube Field-Effect Transistors for Genomic Applications

Single-molecule carbon nanotube-based field-effect transistors are promising all-electronic devices for probing interactions of various biological and chemical molecules at the single- molecule level. Such devices consist of point-functionalized carbon nanotubes which are charge sensitive in the vicinity of a generated defect on the nanotube sidewall. Of particular interest is the characterization of the kinetic rates and thermodynamics of DNA duplex formation through repeated association (hybridization) and dissociation (melting) events on timescales unmatched by conventional single-molecule methods. In this work, we study the kinetics and thermodynamics of DNA duplex formation with two types of single-walled nanotubes: CVD-grown and solution-processed. In both assessments, we are able to extract kinetic and thermodynamic parameters governing the hybridization and melting of DNA oligonucleotides. In the latter case, devices are spun onto a wafer surface from an organic suspension, revealing consistent electrical characteristics. Significant effort is made to expand this work to wafer-level, in an effort to make the fabrication manufacturable

A RF Graphene FET Large-Signal Compact Model Compatible with Circuit Simulators

Graphene, a one-dimensional array of carbon atoms, is a unique material which has yet to be fully utilized. It is being investigated for its applications in the digital, analog, and high frequency (RF) domains. While it lacks a natural bandgap, rendering it unsuitable for digital circuitry without additional modification of electrical characteristics, graphene is applicable to a wide spectrum of RF applications ranging from communications platforms to flexible electronics. Specifically, its use in building RF field-effect transistors (FETs) can lead to better performance metrics, higher bandwidths, and faster data transmission rates. Graphene FETs (GFETs) are attractive because the graphene channel can be grown over large-area surfaces, and the devices typically exhibit high electron and hole mobilities and high achievable current densities [1]. In order to bridge the gap between device simulation and circuit design, a closed-form large-signal compact model compatible with commercially available circuit simulators is desired. The primary investigation of this study is to develop such a model and to evaluate its accuracy with measured and simulated data

Single-Molecule Reaction Chemistry in Patterned Nanowells

A new approach to synthetic chemistry is performed in ultraminiaturized, nanofabricated reaction chambers. Using lithographically defined nanowells, we achieve single-point covalent chemistry on hundreds of individual carbon nanotube transistors, providing robust statistics and unprecedented spatial resolution in adduct position. Each device acts as a sensor to detect, in real-time and through quantized changes in conductance, single-point functionalization of the nanotube as well as consecutive chemical reactions, molecular interactions, and molecular conformational changes occurring on the resulting single-molecule probe. In particular, we use a set of sequential bioconjugation reactions to tether a single-strand of DNA to the device and record its repeated, reversible folding into a G-quadruplex structure. The stable covalent tether allows us to measure the same molecule in different solutions, revealing the characteristic increased stability of the G-quadruplex structure in the presence of potassium ions (K⁺) versus sodium ions (Na⁺). Nanowell-confined reaction chemistry on carbon nanotube devices offers a versatile method to isolate and monitor individual molecules during successive chemical reactions over an extended period of time