Dmitry Shvarts

Direct detection of low-concentration NO in physiological solutions by a new GaAs-based sensor.

Nitric oxide (NO) acts as a signal molecule in the nervous system, as a defense against infections, as a regulator of blood pressure, and as a gate keeper of blood flow to different organs. In vivo, it is thought to have a lifetime of a few seconds. Therefore, its direct detection at low concentrations is difficult. We report on a new type of hybrid, organic-semiconductor, electronic sensor that makes detection of nitric oxide in physiological solution possible. The mode of action of the device is described to explain how its electrical resistivity changes as a result of NO binding to a layer of native hemin molecules. These molecules are self-assembled on a GaAs surface to which they are attached through a carboxylate binding group. The new sensor provides a fast and simple method for directly detecting NO at concentrations down to 1 microM in physiological aqueous (pH=7.4) solution at room temperature.

Self-assembled carbon-nanotube-based field-effect transistors

Self-assembled carbon-nanotube-based field-effect transistors (CNTFETs) were produced with high yield using the natural process of DNA hybridization. In principle, the devices made by this method behave like those made using direct metal-carbon nanotube contacts. The inverse subthreshold slope of the CNTFETs depends on the source-drain voltage applied to the device, confirming that the conductance of CNTFETs is determined by the Schottky barriers at the interfaces between the CNTs and the gold electrodes.

Self-assembled electrical circuits and their electronic properties.

A straightforward method for the self assembly of single walled carbon nanotubes (SWNTs) between gold electrodes was developed. The technique utilizes the hybridization between short complementary DNA sequences located on metal contacts and SWNTs. new technique enables simple production of hundreds of devices with high yields. The electrical characteristics are shown to depend strongly on the existence of the chemical binding groups at the contacts as well as along the tubes. This technique was used to drive the self assembly of SWNT-based field effect transistors (CNTFETs). In principle, the devices made by this method behave like those made using direct metal-carbon nanotube contacts. The inverse subthreshold slope of the CNTFETs depends on the source-drain voltage applied to the device, confirming that the conductance of CNTFETs is determined by the Schottky barriers at the interfaces between the CNTs and the gold electrodes.