Nanotube Molecular Wires as Chemical Sensors (original) (raw)
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Chemical Sensors Based on Carbon Nanotubes: Comparison Between Single and Bundles of Ropes
Sensors and Microsystems - Proceedings of the 12th Italian Conference, 2008
A chemical gas sensor based on a single rope of single walled carbon nanotubes (SWCNTs) has been fabricated first isolating the rope on a silicon/Si 3 N 4 substrate and then realizing, at its ends, two platinum microelectrodes by means of a Focused Ion Beam (FIB). Its electrical behaviour at room temperature in toxic gas environments has been investigated and compared to sensors based on bundles of SWCNT ropes. For all the devices upon exposure to NO2 and NH3 the conductance has been found to increase or decrease respectively. Response time in NO2 is however faster for device based on the single rope. A mechanism for molecular sensing is proposed.
Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors
Applied Physics A
Chemical sensing properties of single wire and mat form sensor structures fabricated from the same carbon nanotube (CNT) materials have been compared. Sensing properties of CNT sensors were evaluated upon electrical response in the presence of five vapours as acetone, acetic acid, ethanol, toluene, and water. Diverse behaviour of single wire CNT sensors was found, while the mat structures showed similar response for all the applied vapours. This indicates that the sensing mechanism of random CNT networks cannot be interpreted as a simple summation of the constituting individual CNT effects, but is associated to another robust phenomenon, localized presumably at CNT-CNT junctions, must be supposed.
Nano Letters, 2003
Arrays of electrical devices with each comprising multiple single-walled carbon nanotubes (SWNT) bridging metal electrodes are obtained by chemical vapor deposition (CVD) of nanotubes across prefabricated electrode arrays. The ensemble of nanotubes in such a device collectively exhibits large electrical conductance changes under electrostatic gating, owing to the high percentage of semiconducting nanotubes. This leads to the fabrication of large arrays of low-noise electrical nanotube sensors with 100% yield for detecting gas molecules. Polymer functionalization is used to impart high sensitivity and selectivity to the sensors. Polyethyleneimine coating affords n-type nanotube devices capable of detecting NO 2 at less than 1 ppb (parts-per-billion) concentrations while being insensitive to NH 3 . Coating Nafion (a polymeric perfluorinated sulfonic acid ionomer) on nanotubes blocks NO 2 and allows for selective sensing of NH 3 . Multiplex functionalization of a nanotube sensor array is carried out by microspotting. Detection of molecules in a gas mixture is demonstrated with the multiplexed nanotube sensors.
Sensors and Actuators B: Chemical, 2008
The effect on the gas sensitivity of point heterocontact between single walled nanotubes (SWNTs) and a gold microwire is demonstrated for the first time. Au-SWNT heterocontact sensors exhibit high sensitivity to NH 3 and NO 2 vapors with fast response and relaxation and demonstrate that these two gases can be distinguished based on the direction of charge transfer between the analyte and the SWNTs. The mechanism of sensing is associated with formation of a thin conductive channel between Au and SWNT, but the sign of the resistance change is controlled by the SWNT.
Carbon nanotubes: Sensor properties. A review
Recent publications dealing with dealing with the fabrication of gas and electrochemical biosensors based on carbon nanotubes have been reviewed. Experimental and theoretical data on the working principles of nanotubes have been presented. The main regularities of the structure, energy parameters and sensor properties of modified semiconducting systems on the basis of cabon nanotubes have been studied by analyzing the mechanisms of nanotubule interaction with functional groups (including carboxyl and amino groups), metallic nanoparticles and polymers leading to the formation of chemically active sensors. The possibility of using boundary modified nanotubes for the identification of metals has been discussed. Simulation results have been reported for the interaction of nanotubes boundary modified by-СООН and-NH 2 groups with atoms and ions of potassium, sodium and lithium. The simulation has been carried out using the molecular cluster model and the MNDO and DFT calculation methods. Sensors fabricated using this technology will find wide application for the detection of metallic atoms and their ions included in salts and alkali.
Ab Initio Study of Doped Carbon Nanotube Sensors
Nano Letters, 2003
Recently great advances have been made in demonstrating the viability of using carbon nanotubes (CNTs) to detect the presence of chemical gases such as NO 2 , NH 3 , and O 2 , and they have led to the design of a new breed of sensor devices. Based on intrinsic CNTs, the devices are capable of detecting small concentration of molecules with high sensitivity under ambient conditions. However, these devices have a limitation that only molecules binding to a carbon nanotube can be detected. They are currently limited to NH 3 , NO 2 , and O 2 , and a host of highly toxic gases (such as carbon monoxide), water molecules, and biomolecules cannot be detected using these intrinsic CNT devices. Recent efforts on externally functionalizing CNT surface and internal doping in CNT only result in temporary sensing capability due to the weak van der Waals interaction between CNT and doped materials. In this paper, we propose the concept of a new type of nanoscale sensor devices that can detect the presence of CO and water molecules. To overcome the reliability problem, these devices are developed by substitutional doping of impurity atoms (such as boron, nitrogen atoms) into intrinsic single-wall carbon nanotubes or by using composite B x C y N z nanotubes. Using first-principle calculations, we demonstrate that these sensor devices can not only detect the presence of CO and water molecules, but also the sensitivity of these devices can be controlled by the doping level of impurity atoms in a nanotube.
Defective carbon nanotubes for single-molecule sensing
Physical Review B, 2009
The sensing ability of metallic carbon nanotubes toward various gas species ͑NO 2 , NH 3 , CO, H 2 O, and CO 2 ͒ is investigated via ab initio calculations and Nonequilibrium Green's Functions technique, focusing on the salient features of the interaction between molecules and oxygenated-defective tubes. As the adsorption/ desorption of molecules induces modulations on the electrical conductivity of the tube, the computation of the electron quantum conductance can be used to predict gas detection. Indeed, the analysis of the conductance curve in a small energy range around the Fermi energy reveal that oxygenated-defective nanotubes are sensitive to NO 2 , NH 3 , CO, and H 2 O, but not to CO 2 . Molecular selectivity can also be provided by the nature of the charge transfer.
Investigation of DNA Decorated Carbon Nanotube Chemical Sensors
MRS Proceedings, 2006
ABSTRACTWe demonstrate a versatile class of nanoscale sensors based on single-stranded DNA (ss-DNA) as the chemical recognition site and single-walled carbon nanotube field effect transistors (swCN-FETs) as the electronic readout component. Coating swCN-FETs with ss-DNA causes a current change when exposed to gaseous analytes, whereas bare swCN-FETs show no detectable change. The responses differ in sign and magnitude depending both on the type of gaseous analyte and the sequence of DNA. Our results suggest that the conformation of ss-DNA on swCN-FET plays a role in determining the sensor response to gaseous analytes. The conformation depends not only on the base content of the oligomer, but also on the specific arrangement of the bases in the ss-DNA. We compare our results with the molecular dynamic simulations for understanding of the sensing mechanisms. SsDNA/swCN-FETs possess rapid recovery and self-regenerating ability, which could lead to realization of large arrays for sensit...
Electrochemically Functionalized Single-Walled Carbon Nanotube Gas Sensor
Electroanalysis, 2006
We demonstrate a facile fabrication method to make chemical gas sensors using single-walled carbon nanotubes (SWNT) electrochemically functionalized with polyaniline (PANI). The potential advantage of this method is to enable targeted functionalization with different materials to allow for creation of high-density individually addressable nanosensor arrays. PANI-SWNT network based sensors were tested for on-line monitoring of ammonia gas. The results show a superior sensitivity of 2.44% DR/R per ppm v NH 3 (which is more than 60 times higher than intrinsic SWNT based sensors), a detection limit as low as 50 ppb v , and good reproducibility upon repeated exposure to 10 ppm v NH 3 . The typical response time of the sensors at room temperature is on the order of minutes and the recovery time is a few hours. Higher sensitivities were observed at lower temperatures. These results indicate that electrochemical functionalization of SWNTs provides a promising new method of creating highly advanced nanosensors with improved sensitivity, detection limit, and reproducibility.