Carboxylic Multi-walled Carbon Nanotubes Research Articles

Excellent and effective interfacial transition layer with an organic/inorganic hybrid carbon nanotube network structure for basalt fiber reinforced high-performance thermoplastic composites

Basalt fiber reinforced high-performance thermoplastic (BFRHTP) composites are promising materials for application in military, aerospace, chemical, automobile, and other high-tech industries. However, their mechanical properties are still largely limited by poor interfacial properties because of the smooth, inert, and low-energy surface of BF. In this study, an organic/inorganic hybrid sizing agent was used for BF surface modification to construct an appropriate modulus transition layer for the interface with a combination of soft and rigid phases. Organic poly(ether nitrile) (PEN) and inorganic carboxylic multi-walled carbon nanotubes (MWCNT-COOH) in hybrid sizing agents (PEN/CNT) were respectively used as soft and rigid phases to design the interfacial structure. The tensile strength, flexural strength, interlaminar and interfacial shear strength of the basalt fiber reinforced poly(phthalazinone ether nitrile ketone) composites were increased by 60, 33, 62, and 144%, respectively. This approach provides a simple, green, and promising strategy for enhancing the interfacial properties of BFRHTP composites.

Electrochemical deposition multi-walled carbon nanotube coatings on the surface of Ti6Al4V alloy for enhancing its biotribological properties

Ti6Al4V alloys have potential applications as bone implants. However, their poor biotribological performances affected the service life. In this work, carboxylic multi-walled carbon nanotubes (CMWNT) coatings were grafted on the surface of Ti6Al4V alloys by electrochemical deposition for enhancing the biotribological properties. The CMWNT coatings showed lower coefficient of friction and wear rates, with the reduction of wear rates of 6% in dry condition and 90% under simulated body fluid (SBF) lubrication. This result might be ascribed to the transfer of friction behavior from sliding friction to rolling friction. In addition, the tribological regularity of CMWNT coating with the frequency and load were discussed. Under dry friction, with the increase of frequency and the decrease of normal load, the COF of the CMWNT coating decreased. In SBF lubrication, the COF decreased and the wear rate increased with the increase of frequency. Moreover, the excellent anti-wear properties were observed at the below of 10 N. These findings indicate that the CMWNT coating has an excellent protective effect on titanium alloy, and has a certain application potential in the biomedical field.

Direct Electrochemistry of Glucose Dehydrogenase-Functionalized Polymers on a Modified Glassy Carbon Electrode and Its Molecular Recognition of Glucose.

A glucose biosensor was layer-by-layer assembled on a modified glassy carbon electrode (GCE) from a nanocomposite of NAD(P)+-dependent glucose dehydrogenase, aminated polyethylene glycol (mPEG), carboxylic acid-functionalized multi-wall carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymers. The electrochemical electrode was denoted as NF/IL/GDH/mPEG-fMWCNTs/GCE. The composite polymer membranes were characterized by cyclic voltammetry, ultraviolet-visible spectrophotometry, electrochemical impedance spectroscopy, scanning electron microscopy, and transmission electron microscopy. The cyclic voltammogram of the modified electrode had a pair of well-defined quasi-reversible redox peaks with a formal potential of -61 mV (vs. Ag/AgCl) at a scan rate of 0.05 V s-1. The heterogeneous electron transfer constant (ks) of GDH on the composite functional polymer-modified GCE was 6.5 s-1. The biosensor could sensitively recognize and detect glucose linearly from 0.8 to 100 µM with a detection limit down to 0.46 μM (S/N = 3) and a sensitivity of 29.1 nA μM-1. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 0.21 mM. The constructed electrochemical sensor was compared with the high-performance liquid chromatography method for the determination of glucose in commercially available glucose injections. The results demonstrated that the sensor was highly accurate and could be used for the rapid and quantitative determination of glucose concentration.

Electrochemical sensor based on carboxylated carbon nanotubes and chromium black T for the detection of ethyl maltol

In this paper, a novel electrochemical sensor based on carboxylated multi-walled carbon nanotubes (C-MWCNTs) and chromium black T (EBT) composites modified electrodes (EBT/C-MWCNTs/GCE) were proposed for the sensitive determination of ethyl maltol (EMA). Cyclic voltammetry and differential pulse voltammetry techniques were used to investigate the performance of EMA on EBT/C-MWCNTs/GCE. The results showed that the peak current of EMA was significantly enhanced by the EBT/C-MWCNTs/GCE compared with the bare glassy carbon electrode. The peak current showed a good linear relationship with the mass concentration of EMA in the range of 10 ∼ 1000 μg/L and the detection limit is 3.3 μg/L. Moreover, the sensor is easy to prepare and shows long term stability, which has great potential application for the determination of EMA in edible oil.

Carboxylic multiwalled carbon nanotube aerogel-based macroscale fiber as a highly porous current collector

Carbon nanotube yarn is a potential substance for the fabrication of fiber-shaped energy storage devices owing to its lightweight, stiffness, and excellent electrical properties. However, it has a compact structure with a limited pore volume, leading to insufficient active material loading and inadequate gel electrolyte penetration. These seriously restrict its application in fiber-shaped energy storage devices made entirely of solid-state components. Herein, glycerol-functionalized polyacrylonitrile nanofibers (GPN) are electro-spun and collected on Ti wire. And they are chosen as hydrophilic support to load carboxylic multiwalled carbon nanotubes (CMWCNTs) via dip-coating. After oxidation, a 3D rolled O-CMWCNTs@GPN/Ti aerogel fiber-shaped structure with macroscopic thickness and excellent stability in water is fabricated. The O-CMWCNTs@GPN/Ti structure has a high length-specific capacitance value of 15.2 mF cm−1 itself. It also can be used as a current collector to load pseudocapacitive materials to improve capacity. With polyaniline (PANI) electrodeposited in this structure, the as-prepared hybrid aerogel electrode PANI@O-CMWCNTs@GPN/Ti displays a high specific capacitance of 52.6 mF cm−1 in a fiber-shaped supercapacitor device. All features suggest that O-CMWCNTs@GPN/Ti aerogel is an excellent candidate for flexible fiber-shaped energy storage devices.

The attenuating ability of deep eutectic solvents towards the carboxylated multiwalled carbon nanotubes induced denatured β-lactoglobulin structure.

The stabilization of proteins has been a major challenge for their practical utilization in industrial applications. Proteins can easily lose their native conformation in the presence of denaturants, which unfolds the protein structure. Since the introduction of deep eutectic solvents (DESs), there are numerous studies in which DESs act as promising co-solvents that are biocompatible with biomolecules. DESs have emerged as sustainable biocatalytic media and an alternative to conventional organic solvents and ionic liquids (ILs). However, the superiority of DESs over the deleterious influence of denaturants on proteins is often neglected. To address this, we present the counteracting ability of biocompatible DESs, namely, choline chloride-glycerol (DES-1) and choline chloride-urea (DES-2), against the structural changes induced in β-lactoglobulin (Blg) by carboxylated multiwalled carbon nanotubes (CA-MWCNTs). The work is substantiated with various spectroscopic and thermal studies. The spectroscopic results revealed that the fluorescence emission intensity enhances for the protein in DESs. Contrary to this, the emission intensity extremely quenches in the presence of CA-MWCNTs. However, in the mixture of DESs and CA-MWCNTs, there was a slight increase in the fluorescence intensity. Circular dichroism spectral studies reflect the reappearance of the native band that was lost in the presence of CA-MWCNTs, which is a good indicator of the counteraction ability of DESs. Further, thermal fluorescence studies showed that the protein exhibited extremely great thermal stability in both DESs as well as in the mixture of DES-CA-MWCNTs compared to the protein in buffer. This study is also supported by dynamic light scattering and zeta potential measurements; the results reveal that DESs were successfully able to maintain the protein structure. The addition of CA-MWCNTs results in complex formation with the protein, which is indicated by the increased hydrodynamic size of the protein. The presence of DESs in the mixture of CA-MWCNTs and DESs was quite successful in eliminating the negative impact of CA-MWCNTs on protein structural alteration. DES-1 proved to be superior to DES-2 over counteraction against CA-MWCNTs and maintained the native conformation of the protein. Overall, both DESs act as recoiling media for both native and unfolded (denatured by CA-MWCNTs) Blg structures. Both the DESs can be described as potential co-solvents for Blg with increased structural and thermal stability of the protein. To the best of our knowledge, this study for the first time has demonstrated the role of choline-based DESs in the mixture with CA-MWCNTs in the structural transition of Blg. The DESs in the mixture successfully enhance the stability of the protein by reducing the perturbation caused by CA-MWCNTs and then amplifying the advantages of the DESs present in the mixture. Overall, these results might find implications for understanding the role of DES-CA-MWCNT mixtures in protein folding/unfolding and pave a new direction for the development of eco-friendly protein-protective solvents.

In vitro comparative cytotoxic assessment of pristine and carboxylic functionalized multiwalled carbon nanotubes on LN18 cells.

Multiwalled carbon nanotubes (MWCNTs) have been used in biomedical applications due to their ability to enter the cells. Carboxylic functionalization of MWCNT (MWCNT-COOH) is used to mitigate the toxicity of MWCNTs. Our study focuses on comparing the toxicity of MWCNT and MWCNT-COOH on the neuronal cells, LN18. Concentrations of 5, 10, 20, and 40 µg ml-1 were used for the study, and cytotoxicity was determined at 0, 1, 3, 6, 12, 24, and 48 h of incubation. Cell viability was assessed by Trypan Blue, MTT, and Live dead cell assays, and the oxidative stress produced was determined by reactive oxygen species (ROS) and Lipid peroxidation assays. MWCNT-COOH showed higher cell viability than MWCNT for 20 and 40 µg ml-1 at 24 and 48 h. This was also visually observed in the live dead cell imaging. However, at 48 h, the morphology of the cells appeared more stretched for all the concentrations of MWCNT and MWCNT-COOH in comparison to the control. A significant amount of ROS production can also be observed at the same concentration and time. Viability and oxidative stress results together revealed that MWCNT-COOH is less toxic when compared to MWCNT at longer incubation periods and higher concentrations. However, otherwise, the effect of both are comparable. A concentration of 5-10 µg ml-1 is ideal while using MWCNT and MWCNT-COOH as the toxicity is negligible. These findings can further be extended to various functionalizations of MWCNT for wider applications.

Core–shell architectured NH2-UiO-66@ZIF-8/multi-walled carbon nanotubes nanocomposite-based sensitive electrochemical sensor towards simultaneous determination of Pb2+ and Cu2+

Amino functionalized zirconium-based metal-organic framework (NH2-UiO-66) and zinc-based zeolitic imidazolate framework (ZIF-8) were integrated to develop a core-shell architectured hybrid material (NH2-UiO-66@ZIF-8, NU66@Z8). The morphology and structure evolutions of core-shell NU6@Z8 were investigated by FE-SEM, XRD, FTIR, and XPS. The NU66@Z8 combined with carboxylated multi-walled carbon nanotubes (CMWCNT) was deposited on a glassy carbon electrode (GCE) for fabricating an electrochemical platform towards detecting Pb2+ and Cu2+. The NU66@Z8/CMWCNT/GCE revealed significantly improved electrochemical performance for determination of Pb2+ and Cu2+ compared with the individual components, which can be attributed to the strong adsorption capacity, unique core-shell structure, and large electrochemical active surface area of NU66@Z8/CMWCNT. Under the optimal conditions, the developed sensor exhibited excellent sensing capability with a low limit of detection (Pb2+,1nM; Cu2+, 10nM) and a wide determination range (Pb2+,0.003-70μM; Cu2+, 0.03-50μM). Thesensor showed highselectivity towards common interfering ions and good repeatability. The real sample recoveries of proposed sensor were in the range 95.0-103% for Pb2+ (RSD ≤ 5.3%) and 94.2-106% for Cu2+ (RSD ≤ 5.9%), suggesting that the NU66@Z8/CMWCNT is suitable for examining trace heavy metals in natural environment.

Phase Change Energy Storage Material with Photocuring, Photothermal Conversion, and Self-Cleaning Performance via a Two-Layer Structure.

Compared with the thermal curing process, the photocuring process has advantages such as high efficiency and less energy consumption. However, the preparation of photocurable phase change materials (PCMs) with photothermal conversion and self-cleaning properties is challenging due to the conflict between the transparency required by the photocurable resin system and the opacity deduced by the large number of fillers required by photothermal conversion and the negative effect of filler steric hindrance on the reaction rate and crystallinity. In this work, a "thiol-ene" click chemical reaction induced using UV was used to prepare photocurable PCMs, followed by spraying a carboxylated multiwalled carbon nanotube (CCNT) suspension (with ethyl acetate) onto the surface to achieve an effective two-layer composite of the PCM and CCNTs, by which the rough surface of the PCM and the interaction offered by the hydrogen bonds on the interface of the PCM and the CCNTs provide sufficient adhesion for the two phases. The "thiol-ene" cross-linked polymer network provided shape stability as a support material. 1-Octadectanethiol (ODT) and beeswax (BW) were encapsulated in the cross-linked polymer network as phase change components, providing phase change latent heat. The CCNT layer provided excellent photothermal conversion and self-cleaning properties. The experimental results show that the latent heat of the PCM can reach 124.2 J/g, the water contact angle is 144°, the photothermal conversion efficiency reaches 75%, and it has significant self-cleaning performance. To the best of our knowledge, this is the first report on a photocurable PCM with photothermal conversion and self-cleaning properties.

Polyaniline-based acid resistant membranes for controllable ion rejection performance

Nanofiltration (NF) membrane with extraordinary acid stability and controllable separation performance is crucial for acidic wastewater treatment. In this study, we reported polyaniline (PANI)-based acid resistant membranes which can realize controllable ion transport under applied potential. To achieve this, electrically conductive membranes (ECMs) were fabricated by incorporating carboxylic multi-walled carbon nanotubes (MWNTs-COOH) and acids doped PANI via in-situ chemical polymerization. The external voltage was applied to manipulate the electrostatic interactions of ECMs with charged ions in order to regulate the ion transport. The results showed that the type of acid dopants (from small acid to polymer acid) affected the physicochemical and electrochemical properties of ECMs, and therefore influenced the ion rejection performance. ECM-PANIPSSA possessed the optimal acid stability performance among the three kinds of ECMs. It was interesting to find that all the ECMs showed elevated ion rejection rate in response to electrical voltage even immersed in the acid solution for different periods. The ion transport behavior in response to applied potential attributed to the interaction of steric hindrance, Donnan effect and dielectric effect. The proposed ion transport mechanism implied that the interaction energy barrier between ions and ECMs showed a significant change as a result of applied potential. For negatively charged membrane, the Donnan potential difference became more obvious under negative voltage, which made ion transfer more difficult. By contrast, negative voltage neutralized part of the positively charged surface, and therefore weakened the electrostatic interaction for positively charged membrane. The ECMs exhibit good ion rejection and membrane permeance by applying electrical voltage, whose performance was comparable to the current acid resistant NF membrane. This work offers a feasible guideline for the development of acid resistant membranes and opens opportunities in controllable ion transport for acidic wastewater treatment.

Scalable preparation of MWCNTs/PAN conductive composite fibers with Tai Chi structure for thermotherapy textiles

Compared with traditional clothing, wearable textiles with physiotherapy were a breakthrough innovation, among which fiber materials with good mechanical properties and excellent electrical conductivity were key. Herein, we prepared profiled conductive composite fibers (PCFs) with Tai Chi structure based on the polyacrylonitrile (PAN) and carboxylic multiwall carbon nanotubes (MWCNTs) by wet spinning, achieving the synchronous improvement of mechanical and conductivity under a small quantity of conductive fillers doped. By changing the angle of spinning, the migration of MWCNTs could be induced and controlled, realizing the preparation of Tai Chi structure. The PAN and MWCNTs were enriched into the axial unilateral of fibers respectively, similar to the Tai Chi structure, when the spinning angle was 30°. The special Tai Chi structure could concentrate carriers to form a continuous and interpenetrating conductive path and retained the good flexibility and tensile strength of composite fibers. The PCFs prepared with 6 wt% MWCNTs loading possessed 51.6 S/cm and 291 MPa. The wearable electric heaters prepared by PCFs could get a comfortable temperature (30 °C ∼ 60 °C) under the safe voltage condition and had good repeatability and stability, which was expected to provide valuable reference for the development of thermotherapy textiles.

Hierarchically flower-like structure assembled with porous nanosheet-supported MXene for ultrathin electromagnetic wave absorption

The design of a hierarchical three-dimensional (3D) structure is beneficial to suppressing the accumulation of MXene flakes and obtaining satisfactory lightweight, efficient, and broadband-absorbing materials. Undoubtedly, the exploration of electromagnetic wave (EMW) absorbing materials with stronger absorption and thinner thickness of multi-component and multi-mechanism synergy is in great demand, but it is still a challenge. In this paper, we report for the first time a well-designed and optimized electrostatic self-assembly anchored Ti3C2Tx nanosheet to prepare porous flower-like Co/ZnO@CMWCNTs/Ti3C2Tx (CZCT) composites. The electromagnetic parameters and EMW absorption properties of carboxylated multi-walled carbon nanotubes (CMWCNTs) and Ti3C2Tx nanosheets can be controlled by adjusting the load of CMWCNTs and Ti3C2Tx nanosheets. Based on the multi-dimensional material collaboration and electromagnetic synergistic strategy, the flower-like CZCT composite achieves a significant minimum reflection loss (RLmin) of −46 dB at a thickness of 1.5 mm. The maximum effective absorption bandwidth (EABmax) of 4 GHz is 1.9 mm. This work provides a simple strategy for building MXene-based composites to achieve efficient EMW absorption materials with lightweight and adjustable EAB.

Ultralight, Elastic, Hybrid Aerogel for Flexible/Wearable Piezoresistive Sensor and Solid-Solid/Gas-Solid Coupled Triboelectric Nanogenerator.

Aerogels have been attracting wide attentions in flexible/wearable electronics because of their light weight, excellent flexibility, and electrical conductivity. However, multifunctional aerogel-based flexible/wearable electronics for human physiological/motion monitoring, and energy harvest/supply for mobile electronics, have been seldom reported yet. In this study, a kind of hybrid aerogel (GO/CNT HA) based on graphene oxide (GO) and carboxylated multiwalled carbon nanotubes (CMWCNTs) is prepared which can not only used as piezoresistive sensors for human motion and physiological signal detections, but also as high performance triboelectric nanogenerator (TENG) coupled with both solid-solid and gas-solid contact electrifications (CE). The repeatedly loading-unloading tests with 20000 cycles exhibit its high and ultrastable piezoresistive sensor performances. Moreover, when the obtained aerogel is used as the electrode of a TENG, high electric output performance is produced due to the synergistic effect of solid-solid, and gas-solid interface CEs (3D electrification: solid-solid interface CE between the two solid electrification layers; gas-solid interface CE between the inner surface of GO/CNT HA and the air filled in the aerogel pores). This kind of aerogel promises good applications for human physiological/motion monitoring and energy harvest/supply in flexible/wearable electronics such as piezoresistive sensors and flexible TENG.

Two Types of Subgroup-Valence Heteroatoms (PIII, TeIV) Synergistically Controlling Octa-CeIII-Encapsulated Heteropolyoxotungstate and Its Electrochemical Recognition Properties.

Rapid development of the synthetic chemistry of polyoxometalates (POMs) has greatly driven the generation of structurally variable innovative POM-based materials. Herein, we synthesized a novel PIII and TeIV synergistically controlling octa-CeIII-encapsulated heteropolyoxotungstate [H2N(CH3)2]11K2Na6H11[Ce8(CH3COO)2(HPIIIO3)2W8O20(H2O)12(B-β-TeW8O30)2(B-α-TeW8O31)4]·64H2O (1). Its distinctive anion skeleton [Ce8(CH3COO)2(HPIIIO3)2W8O20(H2O)12(B-β-TeW8O30)2(B-α-TeW8O31)4]30- is built by two tetra-vacancy [B-β-TeW8O30]8- and four tetra-vacancy [B-α-TeW8O31]10- moieties linked through an inorganic-organic hybrid [Ce8(CH3COO)2(HPIIIO3)2W8O20(H2O)12]26+ {Ce8P2W8} cluster core. Interestingly, {Ce8P2W8} is assembled from four [W2O11]10- groups and two [HPIIIO3]2- anions and eight Ce3+ ions. Besides, 1 was further composited with carboxylated multiwalled carbon nanotube (CMCN), resulting in a bi-component 1/CMCN nanocomposite. An electrochemical recognition platform (named as 1/CMCN/GCE) was built by modifying 1/CMCN on a glassy carbon electrode (GCE) for electrochemical detection of dopamine (DPA) at physiological pH (pH = 7.0). The findings have shown that 1/CMCN/GCE exhibits a good detection limit of 4.95 nM for DPA. This work provides considerable inspiration to promote innovative and rational structure designs of POM-based materials and expand their applications to electrochemical and biological detection fields.

Efficient stacking of glucose/oxygen microfluidic biofuel cells using a single-streamflow channel

The stacking of microfluidic enzymatic biofuel cells (EBFCs) is a lucrative approach to achieve the targeted power requirements of microelectronic devices. Co-laminar flow based microfluidic EBFCs favour easy and cost-effective microfabrication owing to membrane-less architecture. However, stacking of these unit cells in large number is inefficient due to cross-mixing issues, especially in the cells located downstream of the stack. In this article, we present two-dimensional stacking of four single-streamflow-based EBFCs in a cascade-style serpentine-shaped microfluidic channel. A novel attribute of the device is the identical fuel utilisation in all cells due to mixed single electrolyte stream, which results in stable connection efficiencies. In addition, a novel composite material was used as an air-breathing biocathode implementing the cathodic enzyme covalently immobilised onto carboxyl multiwalled carbon nanotubes (MWCNTs). Negatively charged carboxyl MWCNTs were conformally attached to the highly porous structure of Toray carbon paper (TCP) using positively charged polyethyleneimine (PEI) by electrostatic layer-by-layer (LBL) deposition. At the bioanode, the enzyme and mediator were immobilised on the MWCNTs by a cross-linking method. The experimental results showed that enzyme immobilisation increased proportionally with the number of PEI/MWCNTs bilayers on TCP. When the bioelectrode was analysed individually with five layers of MWCNTs via cyclic voltammetry (CV), the catalytic performance was increased by 4.4-fold. Moreover, the unit cells in the microfluidic stacking device were connected in various configurations i.e., all in series, all in parallel, and series/parallel combined configuration. The connection efficiencies obtained for all the configurations were stable, thereby validating the potential of stacking single-stream microfluidic EBFCs in large number to satisfy the power requirements of small-scale electronic devices.

Assembly of an improved hybrid cascade system for complete ethylene glycol oxidation: Enhanced catalytic performance for an enzymatic biofuel cell

We report an Enzymatic Fuel Cell (EFC) combining an enzyme that can cleave carbon-carbon bonds (oxalate oxidase (OxOx)) with an organic catalyst (Pyrene-TEMPO (TEMPO = 2,2,6,6-tetramethyl piperidinyl-N-oxyl)) immobilized on the surface of modified carboxylated multi-walled carbon nanotubes (MWCNT-COOH). This combination gave a hybrid bi-catalyst electrode for complete ethylene glycol (EG) oxidation. The hybrid electrode provided ninefold enhanced catalytic activity (0.17 ± 6 × 10−3 mA cm−2) in the presence of EG as compared to the electrode in the absence of EG (0.018 ± 3 × 10−5 mA cm−2), indicating that the enzyme combined with the organic catalyst improved energy generation through deep EG electrooxidation. Electrochemical impedance spectroscopy reveals that the addition of the enzyme in the electrode containing MWCNT–COOH–Pyrene-TEMPO increased the charge transfer resistance (Rct) and the capacitance of the double layer. Long-term electrolysis for 15 h showed that the hybrid electrode presented outstanding current density and stability. The EG oxidation products were identified and quantified by high-performance liquid chromatography (HPLC-UV/RID). The results confirmed complete EG oxidation in the presence of CO2 in the solution, allowing 10 electrons to be collected from the fuel. Overall, this study illustrates the development of a simple and improved hybrid bi-catalyst electrode for promising applications in small electronic devices.

Effective detection of early Citrus Huanglongbing by polyethyleneimine modified multi-walled carbon nanotubes gas sensor

Citrus Huanglongbing (HLB) is incurable, so it is necessary to develop an accurate and timely detection method for citrus HLB. Volatile organic compounds (VOCs) of plants can be used as an indicator of their health status. Based on the difference of VOCs between healthy and HLB citrus leaves, we designed the polyethyleneimine (PEI)-modified carboxylic multi-walled carbon nanotubes (CNT-COOH) gas sensor and used it in the diagnosis of citrus HLB. Our PEI/CNT-COOH sensor showed significant impedance responses to four citrus HLB biomarkers VOCs (ethylhexanol, phenylacetaldehyde, linalool and methyl salicylate) with sensitivity up to single-digit ppm. We then used the sensor to detect the VOCs in citrus leaves, and found that the diseased citrus can be distinguished from the healthy citrus according to the different response values of the sensor, successfully identified HLB-infected citrus. Compared with the conventional qPCR method, PEI/CNT-COOH sensor not only has higher accuracy, but also can be used in real time field detection of citrus leaves due to its less stringent operating condition and portability.

Detection of CYFRA21-1 in serum by electrochemical immunosensor based on nanocomposite consisting of AuNPs@CMK-3@CMWCNTs

An electrochemical immunosensor based on the modification of nanocomposite was constructed to detect the lung cancer marker Cytokeratin 19 fragment antigen 21-1 (CYFRA21-1). Ordered mesoporous carbon CMK-3 was selected to mix with carboxylated multi-walled carbon nanotubes (CMWCNTs), and their combination could enhance electron transfer efficiency and amplify the electrochemical signal. Furthermore, aurum nanoparticles (AuNPs) were further mixed with the hybrid carbon nanomaterials, which bind antibodies via Au-S bonds and provide numerous of binding sites for antibodies. Finally, CYFRA21-1 could be detected by specific immune response between antigen and antibody by improving the immunosensor sensitivity. The characterization of scanning electron microscopy (SEM) showed that AuNPs were embedded on the surface and interstices of CMK-3@CMWCNTs. The curves of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that the immunsensor was successfully constructed. The constructed immunosensor had a linear range of 0.5 pg/mL to 105 pg/mL for the detection of CYFRA21-1 in serum, and the correlation coefficient (r) was 0.998, with a detection limit of 0.2 pg/mL. Thus, this method is selective and sensitive for getting the accurate and reliable detection results and provides a new method for the CYFRA21-1 ultrasensitive detection in serum.

A reagentless electrochemical immunosensor for sensitive detection of carcinoembryonic antigen based on the interface with redox probe-modified electron transfer wires and effectively immobilized antibody

Convenient and sensitive detection of tumors marked in serum samples is of great significance for the early diagnosis of cancers. Facile fabrication of reagentless electrochemical immunosensor with efficient sensing interface and high sensitivity is still a challenge. Herein, an electrochemical immunosensor was easily fabricated based on the easy fabrication of immunoassay interface with electron transfer wires, confined redox probes, and conveniently immobilized antibodies, which can achieve sensitive and reagentless determination of the tumor marker, carcinoembryonic antigen (CEA). Carboxyl multi-walled carbon nanotubes (MWCNTs) were firstly modified with an electrochemical redox probe, methylene blue (MB), which has redox potentials distinguished from those of redox molecules commonly existing in biological samples (for example, ascorbic acid and uric acid). After the as-prepared MB-modified MWCNT (MWCNT-MB) was coated on the supporting glassy carbon electrode (GCE), the MWCNT-MB/GCE exhibited improved active area and electron transfer property. Polydopamine (PDA) was then in situ synthesized through simple self-polymerization of dopamine, which acts as the bio-linker to covalently immobilize the anti-CEA antibody (Ab). The developed immunosensor could be applied for electrochemical detection of CEA based on the decrease in the redox signal of MB after specific binding of CEA and immobilized Ab. The fabricated immunosensor can achieve sensitive determination of CEA ranging from 10 pg/ml to 100 ng/ml with a limit of detection (LOD) of 0.6 pg/ml. Determination of CEA in human serum samples was also realized with high accuracy.

Carbon Nanotube Coated Fibrous Tubes for Highly Stretchable Strain Sensors Having High Linearity.

Strain sensors are currently limited by an inability to operate over large deformations or to exhibit linear responses to strain. Producing strain sensors meeting these criteria remains a particularly difficult challenge. In this work, the fabrication of a highly flexible strain sensor based on electrospun thermoplastic polyurethane (TPU) fibrous tubes comprising wavy and oriented fibers coated with carboxylated multiwall carbon nanotubes (CNTs) is described. By combining spraying and ultrasonic-assisted deposition, the number of CNTs deposited on the electrospun TPU fibrous tube could reach 12 wt%, which can potentially lead to the formation of an excellent conductive network with high conductivity of 0.01 S/cm. The as-prepared strain sensors exhibited a wide strain sensing range of 0–760% and importantly high linearity over the whole sensing range while maintaining high sensitivity with a GF of 57. Moreover, the strain sensors were capable of detecting a low strain (2%) and achieved a fast response time whilst retaining a high level of durability. The TPU/CNTs fibrous tube-based strain sensors were found capable of accurately monitoring both large and small human body motions. Additionally, the strain sensors exhibited rapid response time, (e.g., 45 ms) combined with reliable long-term stability and durability when subjected to 60 min of water washing. The strain sensors developed in this research had the ability to detect large and subtle human motions, (e.g., bending of the finger, wrist, and knee, and swallowing). Consequently, this work provides an effective method for designing and manufacturing high-performance fiber-based wearable strain sensors, which offer wide strain sensing ranges and high linearity over broad working strain ranges.