Vibronics and plasmonics based graphene sensors.

A high sensitivity and selectivity sensor is proposed using graphene ribbons which are able to read molecular vibrations and molecular electrostatic potentials, acting as an amplifier and as a transducer converting molecular signals into current-voltage quantities of standard electronics. Two sensing mechanisms are used to demonstrate the concept using ab initio density functional methods. By using the terahertz region of the spectrum, we can characterize modes when single molecules are adsorbed on the ribbon surface.

Switchable molecular conductivity.

We demonstrate the switchability of the molecular conductivity of a citrate. This was made possible through mechanical stretching of two conformers of such citrate capped on and linked between gold nanoparticles (AuNPs) self-assembled as a film. On the basis of experimental results, theoretical analysis was conducted using the density function theory and Green's function to study the electron flux in the backbone.

Mechanism of carbon nanotubes unzipping into graphene ribbons.

The fabrication of graphene nanoribbons from carbon nanotubes (CNTs) treated with potassium permanganate in a concentrated sulfuric acid solution has been reported by Kosynkin et al. [Nature (London) 458, 872 (2009)]. Here we report ab initio density functional theory calculations of such unzipping process.

Light-activated molecular conductivity in the photoreactions of vitamin D3.

In this theoretical-experimental approach, we show using ab initio calculations behavior consistent with the activation of 7-dehydrocholesterol, provitamin D(3), as an initial reactant toward ultraviolet-activated reactions of vitamin D(3). We find using molecular orbital theory that a conformation between the provitamin and the vitamin shows higher conductance than those of the reactant and product. We also find experimental evidence of this electrical character by directly measuring current-voltage characteristics on irradiated and nonirradiated samples of the provitamin.

DNA origami impedance measurement at room temperature.

The frequency response of triangular DNA origami is obtained at room temperature. The sample shows a high impedance at low frequencies, e.g.

Current-voltage-temperature characteristics of DNA origami.

The temperature dependences of the current-voltage characteristics of a sample of triangular DNA origami deposited in a 100 nm gap between platinum electrodes are measured using a probe station. Below 240 K, the sample shows high impedance, similar to that of the substrate. Near room temperature the current shows exponential behavior with respect to the inverse of temperature.

Graphene terahertz generators for molecular circuits and sensors.

Using ab initio density functional theory methods, the optimized structure of the single-, double-, and triple-layered graphene nanoribbons with different stacking orders and edges is calculated along with their Raman spectrums. For each case studied, graphene is found to be a potential source of vibrational signals in the terahertz region of the spectrum when molecules or another layer are adsorbed in the surface; this effect is independent of the hydrogen presence at the edges, and the stacking order. The visible low-frequency modes increase with the addition of graphene layers, and the number of modes may be influenced by the type of edges.

Impedance measurements on a DNA junction.

1 microm double-stranded DNA molecules are immobilized between pairs of gold and pairs of platinum microelectrodes with gaps of 0.4 and 1 microm, respectively, and their electrical characteristics are determined under the application of constant and sinusoidal bias voltages. Due to their extremely high impedance for constant voltage bias, the samples of DNA are excellent insulators; however, their impedances show strong frequency dependence in the range of 10 Hz-7.

Nanomicrointerface to read molecular potentials into current-voltage based electronics.

Molecular potentials are unreadable and unaddressable by any present technology. It is known that the proper assembly of molecules can implement an entire numerical processing system based on digital or even analogical computation. In turn, the outputs of this molecular processing unit need to be amplified in order to be useful.

Molecular electrostatic potential devices on graphite and silicon surfaces.

We demonstrate that molecular gates using molecular electrostatic potentials (MEP) can be used on hydrogen-passivated silicon substrates without any disturbance of their behavior in vacuum; however, the use of graphite as a substrate strongly affects such behavior. As expected, the substrate may become one more design variable. The ability to have several substrate alternatives is very important for the practical implementation of this new scenario based on molecular potentials.