Carbon Nanotube-Based Chemical Sensors Meyyappan, M.
Small (Weinheim an der Bergstrasse, Germany),
April 27, 2016, Letnik:
12, Številka:
16
Journal Article
Recenzirano
The need to sense gases and vapors arises in numerous scenarios in industrial, environmental, security and medical applications. Traditionally, this activity has utilized bulky instruments to obtain ...both qualitative and quantitative information on the constituents of the gas mixture. It is ideal to use sensors for this purpose since they are smaller in size and less expensive; however, their performance in the field must match that of established analytical instruments in order to gain acceptance. In this regard, nanomaterials as sensing media offer advantages in sensitivity, preparation of chip‐based sensors and construction of electronic nose for selective detection of analytes of interest. This article provides a review of the use of carbon nanotubes in gas and vapor sensing.
Gas and vapor sensing is important in environmental monitoring, industrial safety, and biomedical diagnostics. Nanomaterials are ideal for developing small, inexpensive and sensitive detectors. A multisensor array chip is used to construct an electronic nose for selective identification of gases and vapors. The use of carbon nanotubes as sensor materials is reviewed, and unaddressed issues and challenges are identified.
Wearable electronics is expected to be one of the most active research areas in the next decade; therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness ...and flexibility, lightweight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating flexible gas sensors for the detection of various hazardous gases, including nitrogen dioxide (NO2), ammonia (NH3), hydrogen (H2), hydrogen sulfide (H2S), carbon dioxide (CO2), sulfur dioxide (SO2), and humidity in wearable technology, is discussed. In addition, applications of graphene-based materials are also summarized in detecting toxic heavy metal ions (Cd, Hg, Pb, Cr, Fe, Ni, Co, Cu, Ag), and volatile organic compounds (VOCs) including nitrobenzene, toluene, acetone, formaldehyde, amines, phenols, bisphenol A (BPA), explosives, chemical warfare agents, and environmental pollutants. The sensitivity, selectivity and strategies for excluding interferents are also discussed for graphene-based gas and chemical sensors. The challenges for developing future generation of flexible and stretchable sensors for wearable technology that would be usable for the Internet of Things (IoT) are also highlighted.
Vacuum tubes that sparked the electronics era had given way to semiconductor transistors. Despite their faster operation and better immunity to noise and radiation compared to the transistors, the ...vacuum device technology became extinct due to the high power consumption, integration difficulties, and short lifetime of the vacuum tubes. We combine the best of vacuum tubes and modern silicon nanofabrication technology here. The surround gate nanoscale vacuum channel transistor consists of sharp source and drain electrodes separated by sub-50 nm vacuum channel with a source to gate distance of 10 nm. This transistor performs at a low voltage (<5 V) and provides a high drive current (>3 microamperes). The nanoscale vacuum channel transistor can be a possible alternative to semiconductor transistors beyond Moore’s law.
A humidity sensor on cellulose paper is demonstrated using single-walled carbon nanotubes functionalized with carboxylic acid. The conductance shift of the nanotube network entangled on the ...microfibril cellulose is utilized for the humidity sensing. Compared to the control sensor made on a glass substrate, the cellulose-mediated charge transport on the paper substrate enhances the sensitivity. The sensor response exhibits linear behavior up to a relative humidity of 75% with good repeatability and low hysteresis. A simple circuit model is used to explain the sensor results. This approach is a step toward future paper electronics for low-cost disposable applications.
We have demonstrated highly sensitive and label-free detection of cardiac troponin I (cTnI), a biomarker for diagnosis of acute myocardial infarction, using silicon nanowire field-effect transistors. ...A honeycomb-like structure is utilized for nanowire configuration to offer improved electrical performance and increased sensing area. The fabricated devices show n-type behavior with a relatively high ON-OFF current ratio, small sub-threshold swing and low gate leakage current. Monoclonal antibodies for cTnI were covalently immobilized on the nanowire surface and the attachment of antibodies is clearly visualized by atomic force microscope. The sensitivity with various concentrations of buffer solution was also investigated in order to determine the optimal buffer condition. The devices exhibit highest sensitivity under buffer solutions with low ion concentration. In addition, the detection limit of the sensor is as low as ∼5pg/mL, the lowest reported in the literature to date and nearly an order of magnitude smaller than the suggested threshold limit. The fabricated devices demonstrate a good selectivity for detecting cTnI.
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•We fabricated novel silicon nanowire biosensors using honeycomb nanowire (HCNW) structure.•The HCNW FETs show excellent electrical characteristics.•The HCNW devices exhibit exceptional sensitivity and selectivity for detecting cTnI.•Our devices show 8 times lower detection limit than the suggested cutoff at 5pg/mL.•Effect of Debye length on sensitivity was analyzed using AFM results and biosensing experiments.
We have investigated the doping effects of surface functionalization and its influence on the carrier mobility of graphene.
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•For the first time, the doping effects of the surface ...functionalization on graphene with aromatic molecule and organic solvents were investigated by Raman and electronic properties.•Raman spectra showed that both PBASE and these two solvents imposed doping effects on graphene.•Electrical measurements further revealed that PBASE imposed a p-doping effect while DMF and CH3OH imposed n-doping effect.•CH3OH causes a much smaller reduction in the carrier mobility of G-FETs than that of DMF.
Aromatic molecule functionalization plays a key role in the development of graphene field-effect transistors (G-FETs) for bio-detection. We have investigated the doping effects of surface functionalization and its influence on the carrier mobility of graphene. The aromatic molecule (1-pyrenebutanoic acid succinimidyl ester, PBASE), which is widely used as a linker to anchor bio-probes, was employed here to functionalize graphene. Dimethyl formamide (DMF) and methanol (CH3OH) were used as two solvents to dissolve PBASE. Raman spectra showed that both PBASE and these two solvents imposed doping effects on graphene. The PBASE was stably immobilized on the graphene surface, which was confirmed by the new peak at around 1623.5cm−1 and the disordered D peak at 1350cm−1. Electrical measurements and Fermi level shift analysis further revealed that PBASE imposes a p-doping effect while DMF and CH3OH impose an n-doping effect. More importantly, CH3OH causes a smaller reduction in the carrier mobility of G-FETs (from 1095.6cm2/Vs to 802.4cm2/Vs) than DMF (from 1640.4cm2/Vs to 5.0cm2/Vs). Therefore, CH3OH can be regarded as a better solvent for the PBASE functionalization. This careful study on the influence of organic solvents on graphene during PBASE functionalization process provides an effective approach to monitor the surface functionalization of graphene.
We propose a detailed mechanism for the growth of vertical graphene by plasma-enhanced vapor deposition. Different steps during growth including nucleation, growth, and completion of the ...free-standing two-dimensional structures are characterized and analyzed by transmission electron microscopy. The nucleation of vertical graphene growth is either from the buffer layer or from the surface of carbon onions. A continuum model based on the surface diffusion and moving boundary (mass flow) is developed to describe the intermediate states of the steps and the edges of graphene. The experimentally observed convergence tendency of the steps near the top edge can be explained by this model. We also observed the closure of the top edges that can possibly stop the growth. This two-dimensional vertical growth follows a self-nucleated, step-flow mode, explained for the first time.
Spiking neural network has attracted much attention due to its efficient learning and recognition capability. Herein, a leaky integrate-and-fire (LIF) neuron is implemented using conventional silicon ...fabrication on 4F2 footprint. A vertical n-p-n back-to-back diode with floating p-base region, referred as biristor, functions as the LIF neuron. A static current drive results in closed loop feedback in the biristor, exhibiting output voltage oscillation due to periodic charging and discharging in the floating p-base. The LIF rate linearly increases with the drive current. A spiking frequency of up to a few kHz is verified.
We address the sensitive detection and discrimination of gases impacting the environment, such as CH₄, NH₃, SO₂, and CO, using a sensor array and aided by principal component analysis (PCA). A ...32-element chemiresistive sensor array consisting of nine different sensor materials including seven types of modified single-walled carbon nanotubes and two types of polymers has been constructed. PCA results demonstrate excellent discriminating ability of the chemiresistor sensor chip in the 1-30 ppm concentration range. The accuracy of the sensor was verified against data collected using cavity ring down spectroscopy. The sensor chip has also been integrated with a smartphone and has been shown to reproduce the sensing performance obtained with the laboratory measurement system.
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