Carbon Nanotube-based Sensors Research Articles

Towards Tailored Carbon Nanotube-Based Fluorescent Sensors

Single-walled carbon nanotubes (SWCNTs) are an emerging building block for nanoscale sensors and labels because of their unique photophysical properties. Semiconducting SWCNTs fluoresce in the tissue transparency near infrared (nIR) window (840 – 1650 nm) and do not bleach. Due to their 1D nature small perturbations in their environment strongly affect their fluorescence. The major challenges in using SWCNTS for sensing is on the one side their purification and on the other side a tailored surface chemistry for molecular recognition and photophysical signal transduction.Here, we present different approaches to tailor SWCNT surface chemistry and fluorescence emission properties for the detection of biologically important metabolites. Firstly, we tuned the sensitivity of ssDNA/SWCNTs against the neurotransmitter dopamine and different plant polyphenols by changing systematically the DNA sequence. In a more rational approach, we engineered DNA strands conjugated to small peptide sequences. In order to enable a ratio-specific linkage, we determined the amount of bound DNA on the SWCNT surface, which was further observed to play an important role in maintaining colloidal stability of the modified ssDNA/SWCNT conjugates. Finally, aptamer-based approaches were used to combine stable surface modification with target selective binding. For all these approaches we demonstrated via nIR-fluorescence spectroscopy and nIR-fluorescence stand-off imaging that tailoring these nanosensors resulted in an increased specificity against their targets, ranging from small chemical communication compounds (dopamine, H2O2) to cell wall components and secreted enzymes and metabolites. Lastly, we demonstrate that these tailored SWCNT sensors can also be transferred to purified nanotube building blocks, which enables a predictable design concept for sensor properties (emission wavelength and target specificity).

Developing Ovarian Cancer Sensors Using Molecular Perceptron

Ovarian cancer patient prognosis and quality of life are significantly affected by the failure to accurately diagnose disease at early stage. Currently, less than 15% of ovarian cancer patients are diagnosed at stage 1, when 5-year survival rates are near 93%. Early detection may save more than 80% of women diagnosed with ovarian cancer. Our goal is to develop clinical long-term implantable carbon nanotube-based sensors for ovarian cancer biomarkers to transiently detect and monitor their levels in patients. The proposed sensors will harness the unique optical properties and sensitivity of single-walled carbon nanotubes. To improve sensitivity and specificity of such sensors, previously developed to detect ovarian cancer biomarkers in vivo, we used molecular perceptron—data analytics-based methods to detect specific spectroscopic fingerprints from the binding of protein biomarkers to the nanotube surface.

Preclinical Imaging and Spectroscopy in the NIR-II Window with Indocyanine Green (ICG) and Single-Walled Carbon Nanotubes

We developed a near-infrared small animal imaging system, IR VIVO, that provides real-time images, videos and spectral imaging in the NIR-I and shortwave infrared (SWIR or NIR-II) regions. We found that SWIR wavelengths can give optimal resolution for in vivo optical imaging of deep organs in mice up to 3 cm due to the low tissue autofluorescence, scattering and absorption of light at these wavelengths. We also showed how this higher penetration depth can enable the detection of small wavelength changes in the emission of carbon nanotube-based sensors implanted in vivo using a continuously tunable filter.First, we demonstrated superior image clarity and penetration depth at NIR-II wavelengths (1000-1700 nm) in vivo using an FDA approved dye, indocyanine green (ICG) in a mouse. We used 780 nm excitation, detection using a Zephir 1.7 InGaAs camera and 1250 nm long-pass emission filter. We found low tissue autofluorescence at 1250 nm. The ICG dye imaging resulted in superior visualization of microvasculature, perfusion, measurement of hearst rate, respiratory rate, hepatobiliary and intestinal contractions. Further anatomical and functional imaging was carried out by looking at the kinetics of ICG, resulting in the identification of different organs.Second, In vivo near-infrared hyperspectral imaging of carbon nanotubes was conducted using a continuously-tunable filter in the imager. A diffraction volume Bragg grating (VBG), was used to provide narrow-band wavelength selection. Coupled with a homogeneous global illumination, spectrally-defined images were acquired in the entire field of view. The result was a dataset containing both 2D spatial information and the full spectrum for each point in the image. We conducted near-infrared hyperspectral imaging of single-walled carbon nanotubes to measure small wavelength changes of the nanotubes implanted into live mice. Hyperspectral measurements of carbon nanotube sensors for lipids in the liver as well as implantable sensors for doxorubicin were conducted, facilitating liver disease monitoring and drug pharmacokinetics measurements.Finally, we believe wide-area NIR-II imaging and spectral/hyperspectral measurements have broad potential applications for the use of carbon nanotubes and other NIR-I/II materials in basic materials/biology, translational, and clinical work, including sensor arrays, point-of-care measurements, implants, whole small animal imaging and intraoperative/surgical imaging.

A Low-Cost Multi-Parameter Water Quality Monitoring System.

Multi-parameter water quality monitoring is crucial in resource-limited areas to provide persistent water safety. Conventional water monitoring techniques are time-consuming, require skilled personnel, are not user-friendly and are incompatible with operating on-site. Here, we develop a multi-parameter water quality monitoring system (MWQMS) that includes an array of low-cost, easy-to-use, high-sensitivity electrochemical sensors, as well as custom-designed sensor readout circuitry and smartphone application with wireless connectivity. The system overcomes the need of costly laboratory-based testing methods and the requirement of skilled workers. The proposed MWQMS system can simultaneously monitor pH, free chlorine, and temperature with sensitivities of 57.5 mV/pH, 186 nA/ppm and 16.9 mV/°C, respectively, as well as sensing of BPA with <10 nM limit of detection. The system also provides seamless interconnection between transduction of the sensors’ signal, signal processing, wireless data transfer and smartphone app-based operation. This interconnection was accomplished by fabricating nanomaterial and carbon nanotube-based sensors on a common substrate, integrating these sensors to a readout circuit and transmitting the sensor data to an Android application. The MWQMS system provides a general platform technology where an array of other water monitoring sensors can also be easily integrated and programmed. Such a system can offer tremendous opportunity for a broad range of environmental monitoring applications.

Copolymer composition tailored carbon nanotube network breakdown and piezoresistivity of ethylene-vinyl acetate electroconductive composites

Herein, the development of carbon nanotube-based electromechanical sensors with excellent sensing range and gauge factor is reported. Electroconductive composites (EPCs) of ethylene–vinyl acetate random copolymer (EVAc) with different ethylene (E) and vinyl acetate (VAc) segment ratios and different volume fractions of carbon nanotube (CNT) were prepared. The E/VAc ratio was found to significantly impact the AC impedance, electron tunneling, CNT-CNT structural breakdown, effective aspect ratio, and electromechanical behavior. The percolation threshold of CNT was lowest in EPCs with VAc 12%; interestingly, though, the effective aspect ratio, as determined from the micromechanical modeling, was considerably increased in EPC with VAc 40%. With an increase in VAc content, the electrical conductivity decreased; however, the electromechanical response improved significantly. Crystalline content, interfacial wetting, critical strain for the shear strain-induced structural breakdown of percolated CNT network, and effective aspect ratio were found to correlate with the superior electromechanics of EVAc/CNT EPC.

Aligned Carbon Nanotube-Based Sensors for Strain Monitoring of Composites

This paper presents a proof of concept of an aligned carbon nanotube (CNT) based strain sensor tested on the surface of a conventional aeronautic laminate. Two type of strain sensors were produced, type S and type T, in which the CNT alignment was parallel (Y) and transversal (X) to strain direction, respectively. Their electrical resistance response was thoroughly evaluated during cyclic tensile tests. Despite some disparities of the relative electrical resistance behavior in specific strain cycles, probably due to one-off interferences in the CNT conductive mechanism, the obtained gauge factor (GF) values were quite stable. Also, the electrical resistance anisotropy was evaluated and its opposite behavior when the samples were strained in Y- and X-directions may be used as strain direction indicator. Being able to quantify and indicate strain direction with just one 10×10 mm CNT patch, this sensor has proven to be suitable for strain sensing applications, namely for structure health monitoring of advanced composites.

Carbon nanotubes-based sensor for ammonia gas detection – an overview

A sensitive, selective and reliable sensing techniques for ammonia (NH3) gas detection have been highly demanded since NH3 is both a commonly utilized gas in various industrial sectors, and considered as a toxic and caustic agent that can threat human health and environment at a certain level of concentrations. In this article, a brief on the fundamental working principles of sensor specifications of the analytes detection techniques relying has been reviewed. Furthermore, the mechanism of NH3 detection and recent progress in the development of advanced carbon nanotubes (CNTs)-based NH3 gas sensors, and their performance towards the hybridization with the conductive polymers wascomprehensively reviewed and summarized. Finally, the future outlook for the development of highperformanceNH3 sensors was presented in the conclusions part.

Comprehensive evaluation of the piezoresistive behavior of carbon nanotube-based composite strain sensors

Theoretical analysis of the piezoresistive behavior of carbon nanotube (CNT)-based composites is of great importance for understanding the electro-mechanical response of CNT-based composite strain sensors. In this paper, a comprehensive analytical model is developed to predict the electro-mechanical response of conductive CNT-based composite sensors by considering some critical factors, such as CNT dimensions, interphase, nanotube waviness, and dispersion state. To acheive this, stretching-induced changes in electrical resistance are characterized in the model by the variation of CNT content, CNT orientation, and percolated conductive networks. Then the effects of these key factors are systematically examined on the piezoresistive response of CNT-based composite strain sensors and found to play important roles in determining the sensitivity. Moreover, comparisons between modelling predictions and existing numerical and experimental data are made to demonstrate the validity of the developed model. The developed model highlights the physical mechanism and takes full consideration of the key parameters, which can help to gain a deeper understanding of the piezoresistive behavior of CNT-based composite sensors compared with existing modellings. Finally, a meaningful recommendation is made to optimize the design of highly sensitive CNT-based composite sensors.

Abstract PO-068: Developing ovarian cancer sensors using molecular perceptron

Abstract Ovarian cancer patient prognosis and quality of life are significantly affected by the failure to accurately diagnose disease at early stage. Currently, less than 15% of ovarian cancer patients are diagnosed at stage 1, when 5-year survival rates are near 93%. Early detection may save more than 80% of women diagnosed with ovarian cancer. Our goal is to develop clinical long-term implantable carbon nanotube-based sensors for ovarian cancer biomarkers to transiently detect and monitor their levels in patients. The proposed sensors will harness the unique optical properties and sensitivity of single-walled carbon nanotubes. To improve sensitivity and specificity of such sensors, previously developed to detect ovarian cancer biomarkers in vivo, we used molecular perceptron—data analytics-based methods to detect specific spectroscopic fingerprints from the binding of protein biomarkers to the nanotube surface. Citation Format: Zvi Yaari, Yoona Yang, Anand Jagota, Ming Zheng, Daniel A. Heller. Developing ovarian cancer sensors using molecular perceptron [abstract]. In: Proceedings of the AACR Virtual Special Conference on Artificial Intelligence, Diagnosis, and Imaging; 2021 Jan 13-14. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(5_Suppl):Abstract nr PO-068.

Ultrathin and Ultrasensitive Printed Carbon Nanotube-Based Temperature Sensors Capable of Repeated Uses on Surfaces of Widely Varying Curvatures and Wettabilities.

In this paper, we demonstrate the ability to fabricate temperature sensors by using our newly developed carbon nanotube-graphene oxide (CNT-GO) ink to print temperature-sensitive traces on highly flexible, thin, and adhesive PET (polyethylene terephthalate) tapes, which in turn are integrated on surfaces of different curvatures and wettabilities. Therefore, the strategy provides a facile, low-cost, and environmentally friendly method to deploy printed temperature sensors on surfaces of widely varying curvatures and wettabilities. The temperature sensing occurs through a thermally induced change in the resistance of the printed traces and we quantify the corresponding negative temperature coefficient of resistance (α) for different conditions of curvatures and wettabilities. In addition, we identify that at low temperatures (below 15 °C), the printed traces show an α value that can be as large (in magnitude) as 60 × 10-3/°C, which is several times higher than the typical α values reported for temperature sensors fabricated with CNT or other materials. Furthermore, we achieve the printing of traces that are only 1-3 μm thick on a 50 μm-thick PET film: therefore, our design represents an ultrathin additively fabricated temperature sensor that can be easily integrated for wearable electronic applications. Finally, we show that despite being subjected to repeated temperature cycling, there is little degradation of the CNT-GO microarchitectures, making these printed traces capable of repeated uses as potential temperature sensors.

Airflow-assisted dielectrophoresis to reduce the resistance mismatch in carbon nanotube-based temperature sensors.

The dielectrophoresis (DEP) method is used to fabricate sensor devices by assembling and aligning carbon nanotubes (CNTs) across electrode structures. The challenges of the method increase as the gap width between the electrodes increases. In this work, a novel DEP setup is proposed to reduce the resistance mismatch in manufacturing carbon nanotube-based sensors. The proposed setup utilizes hot airflow and thermal annealing to fabricate long-aligned multi-walled carbon nanotube (MWCNT) bridges across transparent electrodes with a gap width up to 75 μm. The best alignment results were obtained at airflow velocities between 1.5 m s−1 and 2.5 m s−1. The minimum variation in the resistance of the aligned bridges was 1.81% observed at a MWCNT concentration of 0.005 wt% and deposition time of 10 min. Long MWCNT bridges have many contact points that link MWCNTs to each other, making the contact resistance a robust indicator of the variation in the ambient temperature. The characteristics of the MWCNT bridges as a temperature sensor, including the response, sensitivity, and recovery, were investigated.

In Vivo Biocompatibility of Single Walled Carbon Nanotubes

Ovarian cancer patient prognosis and quality of life are significantly affected by the failure to accurately diagnose disease at early stage. Currently, less than 15% of ovarian cancer patients are diagnosed at stage 1, when 5-year survival rates are near 93%. Early detection may save more than 80% of women diagnosed with ovarian cancer. Our goal is to develop clinical long-term implantable carbon nanotube-based sensors for ovarian cancer biomarkers to transiently detect and monitor their levels in patients. The proposed sensors will harness the unique optical properties and sensitivity of single-walled carbon nanotubes. To improve sensitivity and specificity of such sensors, previously developed to detect ovarian cancer biomarkers in vivo, we used molecular perceptron—data analytics-based methods to detect specific spectroscopic fingerprints from the binding of protein biomarkers to the nanotube surface.

Thermoelastic modeling and comparative analysis of biomass sensors under rippling deformation and magnetic field

This study is intended for investigating the linear and nonlinear responses of carbon nanotube-based mass sensors in thermal and magnetic environment. For accurate modeling, the carbon nanotube rippling deformation effect is considered and various representations for the thermal expansion are examined and compared to each other. By utilizing Euler-Bernoulli beam theory assumptions and Eringen's nonlocal elasticity theory, the nonlinear reduced-order model is developed on the basis of the extended Hamilton's principle. The results show that the natural and resonant frequencies and frequency shifts of the system are strongly dependent on the magnetic field and thermal expansion representation. The method of multiple scale is used to determine the modulation equation including the von Karman and rippling nonlinearities. The results show a very good agreement between the perturbation solution and the numerical integration results for specific conditions of the forcing, temperature difference, and quality factor. A comparative study between the linear and nonlinear mass sensing approaches is performed to show their limits of applicability. It is demonstrated that the linear approach may result in erroneous detection of the deposited mass. The obtained results indicate that the longitudinal magnetic field enhances the dynamic stability of the carbon nanotube mechanical resonator in the pre-buckling oscillation regime, while the dynamic stability of the nanoscale resonator is decreased in the presence of the magnetic field for the post-buckling configuration. Also, the ripple-based nonlinearity is accompanied by an increase in the mass responsivity of the resonator. On the contrary, mass sensitivity of the carbon nanotube resonator is diminished by considering the von Kármán geometric nonlinearity. This study shows the importance of considering the nonlinear effects on the system's sensitivity from frequency and amplitude sensing techniques.

Development of carbon nanotube-based polymer-modified electrochemical sensor for the voltammetric study of Curcumin

ABSTRACT The applicability of Curcumin (CRC) as a medicinal remedy for various health issues and as an anti-inflammatory agent, it is of great importance to develop an effortless, sensitive methodology for its determination. In the present research, CRC was determined electrochemically via voltammetric techniques using poly(L-arginine) modified carbon nanotube paste sensor (PArMCNTPS). Different parameters (pH, scan rate, number of polymerisation cycle) were optimised using cyclic voltammetry. CRC displayed well-defined oxidative and reductive peaks at 0.24 V and 0.16 V, respectively. The efficacy of the electrode towards the concurrent detection of CRC was examined in the presence of Riboflavin and Ascorbic acid. Detection of CRC by PArMCNTPS through differential pulse voltammetry technique was achieved from 2 × 10−7 M to 5 × 10−6 M and it presents adequately low detection (6.62 × 10−8 M) and quantification (2.20 × 10−7 M) limits. Furthermore the developed sensor was employed to determine CRC in turmeric powder to validate its analytical application.

Graphene and carbon nanotube-based high-sensitive film sensors for in-situ monitoring out-of-plane shear damage of epoxy composites

Graphene (GN) and carbon nanotube (CNT) have already been explored their potential crack-monitoring abilities in the field of composite materials, but a relatively low sensitivity to shear damage is still a practical problem. This work aims to improve the monitoring sensitivity to out-of-plane shear damage by constructing hybrid GN/CNT film sensors with a GN weight loading of 0–10%. The prepared GN/CNT sensors are integrated into epoxy composites and both quasi-static and cyclic shear loads are carried out. It is found from quasi-static testing that once the out-of-plane shear damage initiates, relative electrical resistance variation suddenly jumps about 34–191% from the GN/CNT film sensors. Also, the sensitivity coefficient in the crack growth stage could reach 124–684. Namely, the GN/CNT sensors show high monitoring sensitivity to the initiation and growth of out-of-plane shear damage. Moreover, results from cyclic loading further reveal that the GN/CNT sensors possess stable sensitivity to the shear deformation and damage. Meanwhile, similar response trends from an acoustic emission sensor prove the monitoring reliability of the GN/CNT film sensors. The obtained high sensitivity demonstrates that the GN/CNT hybrid film sensors are prospective in the field of structural health monitoring of composite materials.

Metal-decorated carbon nanotubes-based sensor array for simultaneous detection of toxic gases

Herein, we report a toxic gas detector based on an array of metal-decorated multiwalled carbon nanotubes (M-MWCNTs) sensors. The room temperature (20 °C) response of the sensors array towards NO2, H2S, NH3, and CO gases was investigated. The MWCNTs were decorated with transition metals, Pt, Ti, Ag, Ru, and Cu to enhance the sensitivity and selectivity of the carbon nanotubes to the toxic gases. The M-MWCNTs powders were deposited on gold electrodes and printed on flexible Kapton sheets to form the sensors array. CO exhibited the lowest resistance change response for all six sensors (five transition metal-decorated MWCNTs sensors and one pristine MWCNTs-based sensor), with the Ag-MWCNTs sensor exhibiting the highest response of 0.047–100 ppm CO. The Ag-MWCNTs also revealed the relatively highest sensitivity of 0.944 upon exposure to 100 ppm NH3. The Cu-MWCNTs sensor showed the highest sensitivity of 1.75 upon exposure to 10 ppm H2S, while the Pt-MWCNTs sensor showed the highest response of 1.96 upon exposure to 10 ppm NO2. A unique response pattern was generated for each gas that can be used for its identification. The experimental results were also compared to our previously reported density functional theory (DFT) calculations, revealing the same order of resistance change, thereby validating the use of DFT as a tool to predict the interaction properties and providing an in-depth understanding of the reducing/oxidizing gas electron transfer mechanisms.

Improving sensing properties of entangled carbon nanotube-based gas sensors by atmospheric plasma surface treatment

Entangled multi-walled carbon nanotubes (MWCNTs) on polyurethane (PUR) after Ar plasma-treatment and He plasma-treatment have been tested as gas sensors for ethanol sensing. It was found that plasma-treated sensors exhibit higher sensitivity compared to the non-treated samples along with different ethanol concentration. Non-treated sensors exhibit similar sensor response with the increase in ethanol concentration, while Ar plasma-treated sensors displays ~5 times improvement and He plasma-treated sensors show ~3 times improvement with an increase in ethanol concentration. The sensitivity of the plasma-treated sensors is also stable for following two-weeks after the preparation compared to the non-treated sensor. Entangled nanotube network exhibits a significant shift in the baseline resistance after both plasma-treatments. The response time of the sensor was increased after the plasma-treatment, while the recovery was rather quick. Surface analyses revealed that plasma-treatment did not make any significant morphological changes. Thus, the improvements in stability and sensitivity after plasma-treatment are attributed to the plasma-enhanced surface modification and formation of functional bonds on the surface of nanotubes, which are sensitive to the ethanol vapour.

Carbon nanotube-based thin-film resistive sensor for point-of-care screening of tuberculosis.

For point-of-care diagnosis of tuberculosis (TB), current TB diagnostic approaches need to be further improved for achieving an accurate diagnosis that is rapid and low-cost. This paper presents an immuno-resistive sensor on a plastic film for inexpensive, simple TB screening. The sensor is composed of single-walled carbon nanotubes (SWCNTs) functionalized with polyclonal antibodies raised against the MPT64 surface antigen from Mycobacterium tuberculosis (MTB). The target analyte of either MTB or MPT64 is spiked in tongue swab and sputum samples. Under optimized conditions, targets are directly detected from tongue swab samples by resistive measurement. Target analytes spiked into human sputa are enriched with a magnetic bead protocol followed by resistive detection. This highly sensitive film sensor will facilitate rapid TB screening with the added benefits of a small form factor, simple operation, low power requirement, and low cost.

Imaging of Monoamine Neurotransmitters with Fluorescent Nanoscale Sensors.

Cells use biomolecules to convey information. For instance, neurons communicate by releasing chemicals called neurotransmitters, including several monoamines. The information transmitted by neurons is, in part, coded in the type and amount of neurotransmitter released, the spatial distribution of release sites, the frequency of release events, and the diffusion range of the neurotransmitter. Therefore, quantitative information about neurotransmitters at the (sub)cellular level with high spatiotemporal resolution is needed to understand how complex cellular networks function. So far, various analytical methods have been developed and used to detect neurotransmitter secretion from cells. However, each method has limitations with respect to chemical, temporal and spatial resolution. In this review, we focus on emerging methods for optical detection of neurotransmitter release and discuss fluorescent sensors/probes for monoamine neurotransmitters such as dopamine and serotonin. We focus on the latest advances in near infrared fluorescent carbon nanotube-based sensors and engineered fluorescent proteins for monoamine imaging, which provide high spatial and temporal resolution suitable for examining the release of monoamines from cells in cellular networks.

Mass transport of lipopolysaccharide induced H2O2 detected by an intracellular carbon nanoelectrode sensor

Hydrogen peroxide is a key component of the innate immune response, regulating how a cell responds to a bacterial threat; however, being transient in nature makes it extremely difficult to detect. We show the development of an improved biosensor capable of the rapid detection of the hydrogen peroxide produced intracellularly in response to both smooth and rough lipopolysaccharides (LPS) structures. The arising signal and mass transport behaviour to the electrodes were characterised. This response was detected utilising a single walled carbon nanotube-based sensor that has been functionalised with an osmium complex for specificity and detecting the change in intracellular concentrations of hydrogen peroxide through chronoamperometry. This was conducted within murine macrophage (RAW264.7) cells and using ultra-pure LPS extracted from two different serotypes of bacteria (0111:B4 and Re495). This allowed the comparison of the immune response when infected with different structures of LPS. We demonstrate that the hydrogen peroxide signal can be electrochemically detected within 3 seconds post injection. Combining the nature of the mass transport of hydrogen peroxide and concentration characteristics, a bacterial ‘fingerprint’ was identified. The impact of this work will be demonstrated in allowing us to develop a rapid diagnostic for bacterial detection.