Search Results (95)

Electrochemical formation of ceria (mixed Ce₂O₃ and CeO₂) coatings on different types of screen-printed carbon electrodes (SPCEs) (based on graphite (C110), carbon nanotubes (CNT), single-walled carbon nanotubes (SWCNT), carbon nanofibers (CNF), and mesoporous carbon (MC)) were studied. Their potential applications as catalysts for various redox reactions and electrochemical sensors were investigated. The ceria oxide layers were electrodeposited on SPCEs at various current densities and deposition time. The morphology, structure, and chemical composition in the bulk of the ceria layers were studied by SEM and EDS methods. XRD was used to identify the formed phases. The concentration, chemical composition and chemical state of the elements on the surface of studied samples were characterized by XPS. It was established that the increase of the concentration of CeCl₃ in the solution and the cathode current density strongly affected the surface structure and concentration (relation between Ce³⁺ and Ce⁴⁺, respectively) in the formed ceria layers. At low concentration of CeCl₃ (0.1M) and low values of cathode current density (0.5 mA·cm⁻²), porous samples were obtained, while with their increase, the ceria coatings grew denser. Full article

Formaldehyde vapor (HCHO) is a harmful chemical substance and a potential air contaminant, with a permissible level in indoor spaces below 0.08 ppm (80 ppb). Thus, highly sensitive gas sensors for the continuous monitoring of HCHO are in demand. The electrical conductivity of semiconducting nanomaterials (e.g., single-walled carbon nanotubes (SWCNTs)) makes them sensitive to chemical substances adsorbed on their surfaces, and a variety of portable and highly sensitive chemiresistive gas sensors, including those capable of detecting HCHO, have been developed. However, when monitoring low levels of vapors (<1 ppm) found in ambient air, most chemiresistive sensors face practical issues, including false responses to interfering effects (e.g., fluctuations in room temperature and humidity), baseline drift, and the need to apply a purge gas. Here, we report an actuator-driven, purge-free chemiresistive gas sensor that is capable of reliably detecting 0.05 ppm of HCHO in the air. This sensor is composed of an HCHO→HCl converter (powdery hydroxylamine salt, HA), an HCl detector (a SWCNT-based chemiresistor), and an HCl blocker (a thin plastic plate). Upon exposure to HCHO, the HA emits HCl vapor, which diffuses onto the adjacent SWCNTs, increasing their electrical conductivity through p-doping. Meanwhile, inserting a plastic plate between HA and SWCNTs makes the conductivity of SWCNTs insensitive to HCHO. Thus, via periodic actuation (insertion and removal) of the plastic plate, HCHO can be detected reliably over a wide concentration range (0.05–15 ppm) with excellent selectivity over other volatile organic compounds. This actuator-driven system is beneficial because it does not require a purge gas for sensor recovery or baseline correction. Moreover, since the response to HCHO is synchronized with the actuation timing of the plate, even small (~0.8%) responses to 0.05 ppm of HCHO can be clearly separated from larger noise responses (>1%) caused by interfering effects and baseline drift. We believe that this work provides substantial insights into the practical implementation of nanomaterial-based chemiresistive gas sensors. Full article

Carbon nanotubes (CNTs) have emerged as pivotal nanomaterials in sensing technologies owing to their unique structural, electrical, and mechanical properties. Their high aspect ratio, exceptional surface area, excellent electrical conductivity, and chemical tunability enable superior sensitivity and rapid response in various sensor platforms. This review presents a comprehensive overview of recent advancements in CNT-based sensors, encompassing both single-walled (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). We discuss their functional roles in diverse sensing applications, including gas sensing, chemical detection, biosensing, and pressure/strain monitoring. Particular emphasis is placed on the mechanisms of sensing, such as changes in electrical conductivity, surface adsorption phenomena, molecular recognition, and piezoresistive effects. Furthermore, we explore strategies for enhancing sensitivity and selectivity through surface functionalization, hybrid material integration, and nanostructuring. The manuscript also covers the challenges of reproducibility, selectivity, and scalability that hinder commercial deployment. In addition, emerging directions such as flexible and wearable CNT-based sensors, and their role in real-time environmental, biomedical, and structural health monitoring systems, are critically analyzed. By outlining both current progress and existing limitations, this review underscores the transformative potential of CNTs in the design of next-generation sensing technologies across interdisciplinary domains. Full article

Norovirus, a foodborne pathogen, causes a significant economic and health burden globally. Although detection methods exist, they are expensive and non-field deployable. A flow-based dielectrophoretic biosensor was designed for the detection of foodborne pathogenic viruses and was tested using bacteriophage MS2 as a norovirus surrogate. The flow-based MS2 sensor comprises a concentrator and a detector. The concentrator is an interdigitated electrode array designed to impart dielectrophoretic effects to manipulate viral particles toward the detector in a fluidic channel. The detector is made of a silver electrode conjugated with anti-MS2 IgG to allow for antibody–antigen biorecognition events and is supplied with the electrical current for the purpose of measurement. Serially diluted MS2 suspensions were continuously injected into the fluidic channel at 0.1 mL/min. A cyclic voltammogram indicated that current measurements from single-walled carbon nanotube (SWCNT)-coated electrodes increased compared to uncoated electrodes. Additionally, a drop in the current measurements after antibody immobilization and MS2 capture was observed with the developed electrodes. Antibody immobilization at the biorecognition site provided greater current changes with the antibody-MS2 complexes vs. the assays without antibodies. The electric field applied to the fluidic channel at 10 V_pp and 1 MHz contributed to an increase in current changes in response to MS2 bound on the detector and was dependent on the MS2 concentrations in the sample. The developed biosensor was able to detect MS2 with a sensitivity of 10² PFU/mL within 15 min. Overall, this work demonstrates a proof of concept for a rapid and field-deployable strategy to detect foodborne pathogens. Full article

Flexible pressure sensors have drawn growing attention in areas like human physiological signal monitoring and human–computer interaction. Nevertheless, it still remains a significant challenge to guarantee their long-term stability while attaining a wide detection range, a minute pressure testing limit, and high sensitivity. Inspired by the wrinkles on animal skins, this paper introduces a flexible pressure sensor with wrinkled microstructures. This sensor is composed of a composite of reduced graphene oxide (rGO), single-walled carbon nanotubes (SWCNTs), and polydimethylsiloxane (PDMS). After optimizing the proportion of the composite materials, the flexible pressure sensor was manufactured using highly efficient heat-shrinkable films. It has a sensitivity as high as 15.364 kPa⁻¹. Owing to the wrinkled microstructures, the sensor can achieve an ultra-wide pressure detection range, with the maximum reaching 1150 kPa, and is capable of detecting water wave vibrations at the minimum level. Moreover, the wrinkled microstructures were locked by PDMS. The sensor acquired waterproof performance and its mechanical stability was enhanced. Even after 18,000 cycles of repeated loading and unloading, its performance remained unchanged. By combining with an artificial neural network, high-precision recognition of different sounds and postures when grasping different objects was realized, with the accuracies reaching 98.3333% and 99.1111%, respectively. Through the integration of flexible WIFI, real-time wireless transmission of sensing data was made possible. In general, the studied sensor can facilitate the application of flexible pressure sensors in fields such as drowning monitoring, remote traditional Chinese medicine, and intelligent voice. Full article

Semiconducting single-walled carbon nanotubes (SWCNTs) are significantly attractive for thermoelectric generators (TEGs), which convert thermal energy into electricity via the Seebeck effect. This is because the characteristics of semiconducting SWCNTs are perfectly suited for TEGs as self-contained power sources for sensors on the Internet of Things (IoT). However, the thermoelectric performances of the SWCNTs should be further improved by using the power sources. The ideal SWCNTs have a high electrical conductivity and Seebeck coefficient while having a low thermal conductivity, but it is challenging to balance everything. In this study, to improve the thermoelectric performance, we combined two types of SWCNTs: one with a high electrical conductivity (Tuball 01RW03, OCSiAl) and the other with a high Seebeck coefficient and low thermal conductivity (ZEONANO SG101, ZEON). The SWCNT inks were prepared by mixing two types of SWCNTs using ultrasonic dispersion while varying the mixing ratios, and p-type SWCNT films were prepared using vacuum filtration. The highest dimensionless figure-of-merit of 1.1 × 10⁻³ was exhibited at approximately 300 K when the SWCNT film contained the SWCNT 75% of SWCNT (ZEONANO SG101) and 25% of SWCNT (Tuball 01RW03). This simple process will contribute to the prevalent use of SWCNT-TEG as a power source for IoT sensors. Full article

Given the requirement of high-efficiency thermal dissipation for large-aperture space optical remote sensors, a radiator based on single-walled carbon nanotubes (SWCNTs) filled with waterborne polyurethane (SWCNTs/WPU) coatings was proposed in this work. In situ polymerized SWCNTs/WPU coatings allowed for the uniform distribution of acid-purified SWCNTs in WPU matrix. Modified oxygen-containing groups on purified SWCNTs enhanced the interfacial compatibility of SWCNTs/WPU and enabled an improved tensile strength 9 (26.3 MPa) compared to raw-SWCNTs/WPU. A high electrical conductivity of 5.16 W/mK and thermal conductivity of 10.9 S/cm were achieved by adding 49.1 wt.% of SWCNTs. Only 2.85% and 4.2% of declined ratios for electric and thermal conductivities were presented after 1000 bending cycles, demonstrating excellent durability and flexibility. The designed radiator was composed of a heat pipe, SWCNTs/WPU coatings and an aluminum honeycomb core, allowing for −1.6~0.3 °C of temperature difference for the in-orbit temperature and thermal balance experimental temperature of the collector pipe. Moreover, the close temperature difference for the in-orbit and ground temperatures of the radiator indicated that the designed radiator with high heat dissipation met the mechanical environment requirements of a rocket launch. SWCNTs/WPU would be promising electric/thermal interface materials in the application of space optical remote sensors. Full article

Single-walled carbon nanotubes (SWCNTs) offer promise as materials for thermoelectric generators (TEGs) due to their flexibility, durability, and non-toxic nature. However, a key barrier to their application lies in their high thermal conductivity, which hampers the generation of temperature differences in TEGs. To address this challenge, we explored a method of enhancing the heat dissipation of SWCNT-based TEGs by coating SWCNT layers onto polymer mesh sheets. During TEG fabrication, achieving stable n-type SWCNT/mesh sheets proved considerably more challenging than their p-type counterparts. This difficulty stemmed from the inferior dispersibility of the n-type SWCNT ink compared to the p-type SWCNT ink. To produce n-type SWCNT/mesh sheets, we initially prepared p-type SWCNT/mesh sheets using p-type SWCNT ink, subsequently doping them with a cationic surfactant solution to induce n-type characteristics. To stabilize the n-type thermoelectric properties in SWCNT/mesh sheets, we applied a fluoropolymer coating to the SWCNT surfaces, mitigating the adsorption of oxygen molecules. This approach yielded n-type SWCNT/mesh sheets capable of long-term maintenance. Furthermore, flexible TEGs fabricated using both p- and n-type SWCNT/mesh sheets demonstrated an output voltage of 15 mV, which can operate IoT sensors using the latest booster circuits, and a maximum power of 100 nW at a temperature difference of 71 K. Full article

In this study, nanofibers obtained through the electrospinning process are explored for strain-sensing applications. Thermoplastic polyurethane (TPU) flexible structures were fabricated using the solution electrospinning process (SEP) technique. Subsequently, these structures were nanomodified with single-walled carbon nanotubes (SWCNTs) through immersion into an ultrasonicated suspension containing 0.3 wt% SWCNTs. The nanomodification aimed to impart an electrically conductive network to the structures. Micro-tensile tests and electrical resistance measurements were conducted to characterize the apparent mechanical and electrical properties, respectively. The fabricated structures demonstrated potential as wearable strain sensors for monitoring changes in strain across various applications. The samples exhibited excellent performance, high sensitivity, outstanding mechanical properties, and a broad stretching range. Scanning electron microscopy (SEM) observations provided qualitative insights into the activated conductive pathways during operation. Full article

Terbium (III) iodide is an interesting chemical compound with unique chemical properties. The introduction of terbium iodide into single-walled carbon nanotubes (SWCNTs) is an environment-friendly process, and it leads to the development of new nanocomposites with improved properties. The embedded terbium iodide forms new one-dimensional atomic structures inside the SWCNTs. Moreover, the electronic properties of filled SWCNTs are modified. Here, the atomic structures of terbium iodide-filled SWCNTs are investigated using high-resolution transmission electron microscopy, and their microstructure, morphology, and filling degrees are studied. The electronic properties of filled SWCNTs are investigated using spectroscopy. Raman spectroscopy provides information on the charge transfer inside filled SWCNTs. The number of transferred electrons and the charge transfer density along the SWCNT axis are estimated from the Raman spectra. These data on charge transfer are required for the application of terbium iodide-filled SWCNTs in nanoelectronics, thermoelectric power generation, and sensors. The obtained quantitative data reveal the high doping efficiencies of SWCNTs with terbium iodide. This is one of the most effective dopants for SWCNTs. The data show a strong p-doping of SWCNTs with the charge transfer from SWCNTs to terbium iodide. The data from Raman spectroscopy testify to the shift of the Fermi level to the valence band of the SWCNTs. The Fermi level shifts are estimated from these data. They are in the range of 0.3–0.4 eV and are comparable to the values for SWCNTs filled with other rare earth metals using environment-friendly processes. Full article

This study presents a fully automated microfluidic electrochemical sensor for the detection of single-stranded DNA (ssDNA) on the ESSENCE platform. The sensor utilizes functionalized single-walled carbon nanotubes (SWCNTs) with short ssDNA strands immobilized through EDC-NHS coupling, placed between non-planar interdigitated electrodes. The detection process involves sequential flow of a background electrolyte and redox probe through the microfluidic channel before introducing the target DNA solution. The same solution is then circulated to enhance selectivity by removing non-specifically bound targets. Electrochemical impedance signals are acquired after the initial and final flow steps, utilizing changes in impedance spectra to quantify target DNA concentration. To streamline complex flow steps and eliminate manual interventions, the system integrates a fully automated fluid control system with syringe pumps, valves, and pressure sensors. Electrochemical impedance spectroscopy (EIS) data is acquired using the Analog Discovery 2 USB oscilloscope, and LabVIEW automation ensures a seamless transition from sample introduction to data acquisition. The transducer material’s flow-through design enables efficient differentiation between different degrees of base pair mismatches, extending applicability to single nucleotide polymorphisms. The system exhibits high sensitivity, detecting single-stranded DNA at concentrations as low as 1 fM within a rapid 15-min detection time. Its compact design and automated data acquisition make it a promising candidate for point-of-care biomolecule sensing, including antigens and toxins. Future applications involve functionalizing SWCNTs with relevant antibodies to enhance the platform’s capabilities for detecting a diverse range of target molecules in clinical settings. Full article

As power sources for Internet-of-Things sensors, thermoelectric generators must exhibit compactness, flexibility, and low manufacturing costs. Stretchable and flexible painted thermoelectric generators were fabricated on Japanese paper using inks with dispersed p- and n-type single-walled carbon nanotubes (SWCNTs). The p- and n-type SWCNT inks were dispersed using the anionic surfactant of sodium dodecylbenzene sulfonate and the cationic surfactant of dimethyldioctadecylammonium chloride, respectively. The bundle diameters of the p- and n-type SWCNT layers painted on Japanese paper differed significantly; however, the crystallinities of both types of layers were almost the same. The thermoelectric properties of both types of layers exhibited mostly the same values at 30 °C; however, the properties, particularly the electrical conductivity, of the n-type layer increased linearly, and of the p-type layer decreased as the temperature increased. The p- and n-type SWCNT inks were used to paint striped patterns on Japanese paper. By folding at the boundaries of the patterns, painted generators can shrink and expand, even on curved surfaces. The painted generator (length: 145 mm, height: 13 mm) exhibited an output voltage of 10.4 mV and a maximum power of 0.21 μW with a temperature difference of 64 K at 120 °C on the hot side. Full article

Elastic pressure sensors play a crucial role in the digital economy, such as in health care systems and human–machine interfacing. However, the low sensitivity of these sensors restricts their further development and wider application prospects. This issue can be resolved by introducing microstructures in flexible pressure-sensitive materials as a common method to improve their sensitivity. However, complex processes limit such strategies. Herein, a cost-effective and simple process was developed for manufacturing surface microstructures of flexible pressure-sensitive films. The strategy involved the combination of MXene–single-walled carbon nanotubes (SWCNT) with mass-produced Polydimethylsiloxane (PDMS) microspheres to form advanced microstructures. Next, the conductive silica gel films with pitted microstructures were obtained through a 3D-printed mold as flexible electrodes, and assembled into flexible resistive pressure sensors. The sensor exhibited a sensitivity reaching 2.6 kPa⁻¹ with a short response time of 56 ms and a detection limit of 5.1 Pa. The sensor also displayed good cyclic stability and time stability, offering promising features for human health monitoring applications. Full article

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials used in thermoelectric generators (TEGs) to power sensors. However, the limitation of SWCNTs is their high thermal conductivity, which makes it difficult to create a sufficient temperature difference. In this study, we fabricated dip-coated SWCNT/mesh sheets using an SWCNT dispersion. Several types of mesh materials were tested, and the most suitable material was polyphenylene sulfide (PPS). SWCNTs were uniformly deposited on the PPS mesh surface without filling the mesh openings. The SWCNT/PPS mesh sheets exhibited flexibility and free-standing strength. When the edge of the SWCNT/PPS mesh sheets were heated, a higher temperature gradient was produced compared with that of the conventional SWCNT film owing to the increase in heat dissipation. A flexible and free-standing TEG with an area of 1200 mm², fabricated using SWCNT/PPS mesh sheets, exhibited an output voltage of 31.5 mV and maximum power of 631 nW at a temperature difference of 60 K (T_low: 320 K). When the TEG was exposed to wind at 3 m/s, temperature difference further increased, and the performance of the TEG increased by a factor of 1.3 for output voltage and 1.6 for maximum power. Therefore, we demonstrated that the TEG’s performance could be improved using SWCNT/PPS mesh sheets. Full article

Polymer nanocomposites filled with carbon nanoparticles (CNPs) are a hot topic in materials science. This article discusses the current research on the use of these materials as interfacial electron transfer films for solid contact potentiometric membrane sensors (SC-PMSs). The results of a comparative study of plasticized poly (vinyl chloride) (pPVC) matrices modified with single-walled carbon nanotubes (SWCNTs), fullerenes-C60, and their hybrid ensemble (SWCNTs-C60) are reported. The morphological characteristics and electrical conductivity of the prepared nanostructured composite films are reported. It was found that the specific electrical conductivity of the pPVC/SWCNTs-C60 polymer film was higher than that of pPVC filled with individual nanocomponents. The effectiveness of this composite material as an electron transfer film in a new potentiometric membrane sensor for detecting phenylpyruvic acid (in anionic form) was demonstrated. Screening for this metabolic product of phenylalanine in body fluids is of significant diagnostic interest in phenylketonuria (dementia), viral hepatitis, and alcoholism. The developed sensor showed a stable and fast Nernstian response for phenylpyruvate ions in aqueous solutions over the wide linear concentration range of 5 × 10⁻⁷–1 × 10⁻³ M, with a detection limit of 10^−7.2 M. Full article