On-Chip Micro Gas Chromatograph Enabled by a Noncovalently Functionalized Single-Walled Carbon Nanotube Sensor Array (original) (raw)
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Electronic sensors for volatile organic compounds have been prepared by drop-casting dispersions of multi-wall carbon nanotubes (MWCNTs) in aqueous solutions of λ-DNA onto Pt microband electrodes. The MWCNTs themselves show a metal-like temperature dependence of the conductance, but the conductance of DNA/MWCNT composites has an activated component that corresponds to inter-tube tunneling. The resistance of the composite was modelled by a series combination of a term linear in temperature for the nanotubes and a stretched exponential form for the inter-tube junctions. The resistance may increase or decrease with temperature according to the composition and may be tuned to be almost temperature-independent at 67% by mass of DNA. Upon exposure to organic vapours, the resistance of the composites increases and the timedependence of this signal is consistent with diffusion of the vapour into the composite. The fractional change in resistance at steady-state provides an analytical signal with a linear calibration and the presence of DNA enhances the signal and adjusts the selectivity in favour of polar analytes. The temperature dependence of the signal is determined by the enthalpy of adsorption of the analyte in the inter-tube junctions and may be satisfactorily modelled using the Langmuir isotherm. Temperature and pressure-dependent studies indicate that neither charge injection by oxidation/ reduction of the analyte nor condensation of analyte on the device is responsible for the signal. We suggest that the origin of the sensing response is an adsorption of the analyte in the inter-tube regions that modulates the tunneling barriers. This suggests a general route to tuning the selectivity of MWCNT gas sensors using non-conductive polymers of varying chemical functionality.
Robust fabrication of selective and reversible polymer coated carbon nanotube-based gas sensors
Sensors and Actuators B: Chemical, 2010
In this study, a systematic investigation was carried out to produce reliable and reproducible polymer coated nanotube sensors to enhance their selectivity against exposed analyte molecules. To do this, a series of uniformly distributed, randomly aligned SWNT films were prepared via vacuum filtration from suspended HiPCO nanotubes and transferred to photolithography patterned silicon chips with high reproducibility and yield. The SWNT film density was optimized for detection of dimethyl methylphosphonate and ammonia at the percolation threshold range of nanotube electric conductance. Cyclic voltammetry (CV) was used to polymerize seven different polymers in aqueous solutions and coat a thin layer onto optimized SWNT films. Polymer coated SWNT-based sensors were analyzed for selectivity for a variety of gases. Results indicate that the electropolymerization of different polymers onto nanotube surfaces can be a simple and promising way to obtain controlled, reliable, and modulated response for various analyte molecules.
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.
Flexible carbon nanotube sensors for nerve agent simulants
Nanotechnology, 2006
Chemiresistor-based vapour sensors made from network films of single-walled carbon nanotube (SWNT) bundles on flexible plastic substrates (polyethylene terephthalate, PET) can be used to detect chemical warfare agent simulants for the nerve agents Sarin (diisopropyl methylphosphonate, DIMP) and Soman (dimethyl methylphosphonate, DMMP). Large, reproducible resistance changes (75-150%), are observed upon exposure to DIMP or DMMP vapours, and concentrations as low as 25 ppm can be detected. Robust sensor response to simulant vapours is observed even in the presence of large equilibrium concentrations of interferent vapours commonly found in battle-space environments, such as hexane, xylene and water (10 000 ppm each), suggesting that both DIMP and DMMP vapours are capable of selectively displacing other vapours from the walls of the SWNTs. Response to these interferent vapours can be effectively filtered out by using a 2 µm thick barrier film of the chemoselective polymer polyisobutylene (PIB) on the SWNT surface. These network films are composed of a 1-2 µm thick non-woven mesh of SWNT bundles (15-30 nm diameter), whose sensor response is qualitatively and quantitatively different from previous studies on individual SWNTs, or a network of individual SWNTs, suggesting that vapour sorption at interbundle sites could be playing an important role. This study also shows that the line patterning method used in device fabrication to obtain any desired pattern of films of SWNTs on flexible substrates can be used to rapidly screen simulants at high concentrations before developing more complicated sensor systems.
Nanotube Molecular Wires as Chemical Sensors
Science, 2000
Chemical sensors based on individual single-walled carbon nanotubes (SWNTs) are demonstrated. Upon exposure to gaseous molecules such as NO 2 or NH 3 , the electrical resistance of a semiconducting SWNT is found to dramatically increase or decrease. This serves as the basis for nanotube molecular sensors. The nanotube sensors exhibit a fast response and a substantially higher sensitivity than that of existing solid-state sensors at room temperature. Sensor reversibility is achieved by slow recovery under ambient conditions or by heating to high temperatures. The interactions between molecular species and SWNTs and the mechanisms of molecular sensing with nanotube molecular wires are investigated.
physica status solidi (a), 2010
The control of molecular architecture provided by the layer-bylayer (LbL) technique has led to enhanced biosensors, in which advantageous features of distinct materials can be combined. Full optimization of biosensing performance, however, is only reached if the film morphology is suitable for the principle of detection of a specific biosensor. In this paper, we report a detailed morphology analysis of LbL films made with alternating layers of single-walled carbon nanotubes (SWNTs) and polyamidoamine (PAMAM) dendrimers, which were then covered with a layer of penicillinase (PEN). An optimized performance to detect penicillin G was obtained with 6-bilayer SWNT/PAMAM LbL films deposited on p-Si-SiO 2 -Ta 2 O 5 chips, used in biosensors based on a capacitive electrolyteinsulator-semiconductor (EIS) and a light-addressable potentiometric sensor (LAPS) structure, respectively. Field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) images indicated that the LbL films were porous, with a large surface area due to interconnection of SWNT into PAMAM layers. This morphology was instrumental for the adsorption of a larger quantity of PEN, with the resulting LbL film being highly stable. The experiments to detect penicillin were performed with constant-capacitance (ConCap) and constant-current (CC) measurements for EIS and LAPS sensors, respectively, which revealed an enhanced detection signal and sensitivity of ca. 100 mV/decade for the field-effect sensors modified with the PAMAM/SWNT LbL film. It is concluded that controlling film morphology is essential for an enhanced performance of biosensors, not only in terms of sensitivity but also stability and response time.
Journal of the American Chemical Society, 2010
We report for the first time single wall carbon nanotubes (SWNTs)-based chemiresistive affinity sensors for highly sensitive and selective detection of small and/or weak-/un-charged molecules using displacement format. The detection of glucose, a small weakly charged molecule, by displacement of plant lectin, Concavalin A, bound to polysaccharide, dextran, immobilized on SWNTs, with picomolar sensitivity and selectivity over other sugars and human serum proteins is demonstrated as a proof-of-concept. In recent years, there has been an increasing interest on use of one-dimensional (1-D) nanostructures, such as nanowires, nanobelts and nanotubes, as transducer elements in affinity (bio)sensors. Use of nanomaterials provide high sensitivity with low limit of detection and in conjunction with molecular recognition element, high selectivity, for labelfree, rapid and low-cost, multiplexed and point-of-care/field detection of various analytes. Single-walled carbon nanotubes (SWNTs) are one such class of nanomaterials that have been used extensively as sensing elements due to their excellent electrical properties, ultrahigh surface area to volume ratio and surface atoms which are extremely sensitive to any surface adsorption/reaction events. SWNTs modified with biorecognition molecules such as antibodies, aptamers or DNA have been successfully used to detect various targets ranging from proteins, 1 viruses, 2 bacteria, 3 yeast, 4 DNA/RNA 5 and even mammalian cancer cells. 6 Majority of these SWNT-based biosensors are affinity sensors wherein the binding of the analyte, generally a large charged antigen, to the bioreceptor immobilized on the surface of SWNTs leads to change in conductance of SWNTs channel. Small, charged or uncharged, molecules constitute a large group of analytes of interest in the fields of environmental monitoring and health care. The detection of these analytes using SWNTs-based chemiresistive/field-effect transistor sensors using the traditional modes of affinity-based sensing might be ineffective as their binding to the recognition molecule might not generate measurable change in conductance/resistance. Nanobiosensors that can detect and quantify such small molecules with high sensitivity and selectivity are therefore in urgent need. In an effort to achieve these objectives, we have for the first time employed
Journal of The American Chemical Society, 2004
It has been reported that protein adsorption on single-walled carbon nanotube field effect transistors (FETs) leads to appreciable changes in the electrical conductance of the devices, a phenomenon that can be exploited for label-free detection of biomolecules with a high potential for miniaturization. This work presents an elucidation of the electronic biosensing mechanisms with a newly developed microarray of nanotube "micromat" sensors. Chemical functionalization schemes are devised to block selected components of the devices from protein adsorption, self-assembled monolayers (SAMs) of methoxy(poly-(ethylene glycol))thiol (mPEG-SH) on the metal electrodes (Au, Pd) and PEG-containing surfactants on the nanotubes. Extensive characterization reveals that electronic effects occurring at the metal-nanotube contacts due to protein adsorption constitute a more significant contribution to the electronic biosensing signal than adsorption solely along the exposed lengths of the nanotubes.
Creation of carbon nanotube based bioSensors through dielectrophoretic assembly
Proceedings of SPIE, 2015
Due to their excellent electrical, optical, and mechanical properties, nanosized single wall carbon nanotubes (SWNTs) have attracted significant attention as a transducing element in nano-bio sensor research. Controlled assembly, device fabrication, and bio-functionalization of the SWNTs are crucial in creating the sensors. In this study, working biosensor platforms were created using dielectrophoretic assembly of single wall carbon nanotubes (SWNTs) as a bridge between two gold electrodes. SWNTs in a commercial SDS surfactant solution were dispensed in the gap between the two gold electrodes, followed by applying an ac voltage across the two electrodes. The dielectrophoresis aligns the CNTs and forms a bridge between the two electrodes. A copious washing and a subsequent annealing of the devices at 200 ᵒC remove the surfactants and create an excellent semiconducting (p-type) bridge between the two electrodes. A liquid gated field effect transistor (LGFET) was built using DI water as the gate dielectric and the SWNT bridge as the channel. Negative gate voltages of the FET increased the drain current and applying a positive gate voltage of +0.5V depleted the channel of charges and turned the device off. The biosensor was verified using both the two terminal and three terminal devices. Genomic salmon DNA dissolved in DI water was applied on the SWNT bridge in both type of devices. In the two terminal device, the conductance of the bridge dropped by 65x after the binding of the DNA. In the LGFET, the transconductance of the device decreased 2X after the binding of the DNA. The binding of the DNA also suppressed hysteresis in the Drain Current vs Gate Voltage characteristics of the LGFET.