Ultrasensitive Carbon Monoxide Gas Sensor at Room Temperature Using Fluorine-Graphdiyne.

Currently, most carbon monoxide (CO) gas sensors work at high temperatures of over 150 °C. Developing CO gas sensors that operate at room temperature is challenging because of the sensitivity trade-offs. Here, we report an ultrasensitive CO gas sensor at room temperature using fluorine-graphdiyne (F-GDY) in which electrons are increased by light. The GDY films used as channels of field-effect transistors were prepared by using chemical vapor deposition and were characterized by using various spectroscopic techniques. With exposure to UV light, F-GDY showed a more efficient photodoping effect than hydrogen-graphdiyne (H-GDY), resulting in a larger negative shift in the charge neutral point (CNP) to form an n-type semiconductor and an increase in the Fermi level from -5.27 to -5.01 eV. Upon CO exposure, the negatively shifted CNP moved toward a positive shift, and the electrical current decreased, indicating electron transfer from photodoped GDYs to CO. Dynamic sensing experiments demonstrated that negatively charged F-GDY is remarkably sensitive to an electron-deficient CO gas, even with a low concentration of 200 parts per billion. This work provides a promising solution for enhancing the CO sensitivity at room temperature and expanding the application of GDYs in electronic devices.

Effects of Dielectric Barrier on Water Activation and Phosphorus Compound Digestion in Gas-Liquid Discharges.

To generate a stable and effective air-liquid discharge in an open atmosphere, we investigated the effect of the dielectric barrier on the discharge between the pin electrode and liquid surface in an atmospheric-pressure plasma reactor. The atmospheric-pressure plasma reactor used in this study was based on a pin-plate discharge structure, and a metal wire was used as a pin-type power electrode. A plate-type ground electrode was placed above and below the vessel to compare the pin-liquid discharge and pin-liquid barrier discharge (PLBD). The results indicated that the PLBD configuration utilizing the bottom of the vessel as a dielectric barrier outperformed the pin-liquid setup in terms of the discharge stability and that the concentration of reactive species was different in the two plasma modes. PLBD can be used as a digestion technique for determining the phosphorus concentration in natural water sources. The method for decomposing phosphorus compounds by employing PLBD exhibited excellent decomposition performance, similar to the performance of thermochemical digestion-an established conventional method for phosphorus detection in water. The PLBD structure can replace the conventional chemical-agent-based digestion method for determining the total dissolved phosphorus concentration using the ascorbic acid reduction method.

Ion-Selective Electrode Based on a Novel Biomimetic Nicotinamide Compound for Phosphate Ion Sensor.

Phosphorus is not only an import nutrient to aquatic habitats, but it also acts as a growth inhibitor in aquatic ecosystems; however, it also aggravates environmental issues, such as eutrophication. There is a growing interest in rapid phosphorus detection to manage and protect water resources. Due to the large molecular structure and high hydration energy of phosphate ions, ion-selective electrodes (ISEs) remain in their infancy for real-time measurements in terms of practical application. In this study, a newly developed ionophore based on a biomimetic nicotinamide functional group was used to detect phosphate selectively, displaying efficient binding through charge interactions and hydrogen bonds. The ISE membrane containing silicone rubber demonstrated an effective detection performance over a long period of time. With a dynamic range between 10-6 and 10-2 M and a limit of detection of 0.85 × 10-6 M (26 µg/L), the newly synthesized ISE membranes demonstrated selectivity for phosphate ions over other ions, including acetate, sulfate, and chloride.

Reusable and pH-Stable Luminescent Sensors for Highly Selective Detection of Phosphate.

Phosphate sensors have been actively studied owing to their importance in water environment monitoring because phosphate is one of the nutrients that result in algal blooms. As with other nutrients, seamless monitoring of phosphate is important for understanding and evaluating eutrophication. However, field-deployable phosphate sensors have not been well developed yet due to the chemical characteristics of phosphate. In this paper, we report on a luminescent coordination polymer particle (CPP) that can respond selectively and sensitively to a phosphate ion against other ions in an aquatic ecosystem. The CPPs with an average size of 88.1 ± 12.2 nm are embedded into membranes for reusable purpose. Due to the specific binding of phosphates to europium ions, the luminescence quenching behavior of CPPs embedded into membranes shows a linear relationship with phosphate concentrations (3-500 µM) and detection limit of 1.52 µM. Consistent luminescence signals were also observed during repeated measurements in the pH range of 3-10. Moreover, the practical application was confirmed by sensing phosphate in actual environmental samples such as tap water and lake water.

Potential Application of Pin-to-Liquid Dielectric Barrier Discharge Structure in Decomposing Aqueous Phosphorus Compounds for Monitoring Water Quality.

Here, we proposed a pin-to-liquid dielectric barrier discharge (DBD) structure that used a water-containing vessel body as a dielectric barrier for the stable and effective treatment of aqueous solutions in an open atmosphere. To obtain an intense pin-to-liquid alternating current discharge using a dielectric barrier, discharge characteristics, including the area and shape of a ground-plate-type electrode, were investigated after filling the vessel with equivalent amounts of water. Consequently, as the area of the ground electrode increased, the discharge current became stronger, and its timing became faster. Moreover, we proposed that the pin-to-liquid DBD reactor could be used to decompose phosphorus compounds in water in the form of phosphate as a promising pretreatment method for monitoring total phosphorus in water. The decomposition of phosphorus compounds using the pin-to-liquid DBD reactor demonstrated excellent performance-comparable to the thermochemical pretreatment method-which could be a standard pretreatment method for decomposing phosphorus compounds in water.

Ultrafast Room Temperature Synthesis of Porous Polythiophene via Atmospheric Pressure Plasma Polymerization Technique and Its Application to NO2 Gas Sensors.

New nanostructured conducting porous polythiophene (PTh) films are directly deposited on substrates at room temperature (RT) by novel atmospheric pressure plasma jets (APPJs) polymerization technique. The proposed plasma polymerization synthesis technique can grow the PTh films with a very fast deposition rate of about 7.0 µm·min-1 by improving the sufficient nucleation and fragment of the thiophene monomer. This study also compares pure and iodine (I2)-doped PTh films to demonstrate the effects of I2 doping. To check the feasibility as a sensing material, NO2-sensing properties of the I2-doped PTh films-based gas sensors are also investigated. As a result, the proposed APPJs device can produce the high density, porous and ultra-fast polymer films, and polymers-based gas sensors have high sensitivity to NO2 at RT. Our approach enabled a series of processes from synthesis of sensing materials to fabrication of gas sensors to be carried out simultaneously.

Highly stretchable, mechanically stable, and weavable reduced graphene oxide yarn with high NO2 sensitivity for wearable gas sensors.

Stretchable gas sensors are important components of wearable electronic devices used for human safety and healthcare applications. However, the current low stretchability and poor stability of the materials limit their use. Here, we report a highly stretchable, stable, and sensitive NO2 gas sensor composed of reduced graphene oxide (RGO) sheets and highly elastic commercial yarns. To achieve high stretchability and good stability, the RGO sensors were fabricated using a pre-strain strategy (strain-release assembly). The fabricated stretchable RGO gas sensors showed high NO2 sensitivity (55% at 5.0 ppm) under 200% strain and outstanding mechanical stability (even up to 5000 cycles at 400% applied strain), making them ideal for wearable electronic applications. In addition, our elastic graphene gas sensors can also be woven into fabrics and clothes for the creation of smart textiles. Finally, we successfully fabricated wearable gas-sensing wrist-bands from superelastic graphene yarns and stretchable knits to demonstrate a wearable electronic device.

Atmospheric Pressure Plasma Polymerization Synthesis and Characterization of Polyaniline Films Doped with and without Iodine.

Although polymerized aniline (polyaniline, PANI) with and without iodine (I2) doping has already been extensively studied, little work has been done on the synthesis of PANI films using atmospheric pressure plasma (APP) deposition. Therefore, this study characterized pure and I2-doped PANI films synthesized using an advanced APP polymerization system. The I2 doping was conducted ex-situ and using an I2 chamber method following the APP deposition. The pure and I2-doped PANI films were structurally analyzed using field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and time of flight secondary ion mass spectrometry (ToF-SIMS) studies. When increasing the I2 doping time, the plane and cross-sectional SEM images showed a decrease in the width and thickness of the PANI nanofibers, while the AFM results showed an increase in the roughness and grain size of the PANI films. Moreover, the FT-IR, XPS, and ToF-SIMS results showed an increase in the content of oxygen-containing functional groups and C=C double bonds, yet decrease in the C-N and C-H bonds when increasing the I2 doping time due to the reduction of hydrogen in the PANI films via the I2. To check the suitability of the conductive layer for polymer display applications, the resistance variations of the PANI films grown on the interdigitated electrode substrates were also examined according to the I2 doping time.

Conductive Polymer Synthesis with Single-Crystallinity via a Novel Plasma Polymerization Technique for Gas Sensor Applications.

This study proposes a new nanostructured conductive polymer synthesis method that can grow the single-crystalline high-density plasma-polymerized nanoparticle structures by enhancing the sufficient nucleation and fragmentation of the pyrrole monomer using a novel atmospheric pressure plasma jet (APPJ) technique. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM) results show that the plasma-polymerized pyrrole (pPPy) nanoparticles have a fast deposition rate of 0.93 µm·min-1 under a room-temperature process and have single-crystalline characteristics with porous properties. In addition, the single-crystalline high-density pPPy nanoparticle structures were successfully synthesized on the glass, plastic, and interdigitated gas sensor electrode substrates using a novel plasma polymerization technique at room temperature. To check the suitability of the active layer for the fabrication of electrochemical toxic gas sensors, the resistance variations of the pPPy nanoparticles grown on the interdigitated gas sensor electrodes were examined by doping with iodine. As a result, the proposed APPJ device could obtain the high-density and ultra-fast single-crystalline pPPy thin films for various gas sensor applications. This work will contribute to the design of highly sensitive gas sensors adopting the novel plasma-polymerized conductive polymer as new active layer.

Durability Improvement of Solid Electrolyte CO2 Sensor Against Humidity Variations.

The sensing materials of potentiometric CO2 sensors utilize alkali/alkali-earth metal carbonates or their combinations. However, lithium carbonate easily responds to humidity resulting in incorrect information regarding CO2 concentration. Herein, the authors report a new sensing material combination (Li2CO3/BaCO3/LiOH/Ba(OH)2 (1:2:0.05:0.1 molar ratio)) for a potentiometric CO2 sensor that is not affected by humidity. The electromotive force (EMF) of the sensor using a combination of Li2CO3, BaCO3, LiOH, and Ba(OH)2 drifted by 1.5% when the relative humidity was changed from 25% to 70%, which is superior to a drift of 6% of a sensor using Li2CO3 and BaCO3, as this sensing material is known to be robust to changes in humidity.

Ultrasensitive and highly selective graphene-based single yarn for use in wearable gas sensor.

Electric components based on fibers or textiles have been investigated owing to their potential applications in wearable devices. High performance on response to gas, drape-ability and washing durability are of important for gas sensors based on fiber substrates. In this report, we demonstrate the bendable and washable electronic textile (e-textile) gas sensors composed of reduced graphene oxides (RGOs) using commercially available yarn and molecular glue through an electrostatic self-assembly. The e-textile gas sensor possesses chemical durability to several detergent washing treatments and mechanical stability under 1,000 bending tests at an extreme bending radius of 1 mm as well as a high response to NO2 gas at room temperature with selectivity to other gases such as acetone, ethanol, ethylene, and CO2.

A 3D scaffold for ultra-sensitive reduced graphene oxide gas sensors.

An ultra-sensitive gas sensor based on a reduced graphene oxide nanofiber mat was successfully fabricated using a combination of an electrospinning method and graphene oxide wrapping through an electrostatic self-assembly, followed by a low-temperature chemical reduction. The sensor showed excellent sensitivity to NO2 gas.

Volatile organic compound gas sensor based on aluminum-doped zinc oxide with nanoparticle.

Thick film semiconductor gas sensors based on aluminum-doped zinc oxide (AZO) with nanoparticle size were fabricated to detect volatile organic compound (VOC) existed in building, especially, formaldehyde (HCHO) gas which was known as the cause of sick building syndrome. The sensing materials for screen printing were prepared using roll milling process with binder. The crystallite sizes of prepared materials were about 15 nm through X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Gas response characteristics were examined for formaldehyde (HCHO), benzene, carbon monoxide, carbon dioxide gas existing in building. In particular, the sensors showed responses to HCHO gas at sub ppm as a function of operating temperatures and gas concentrations. Also, we investigated sensitivity, repeativity, selectivity, and response time of sensor. The transients were very sharp, taking less than 2 s for 90% response. The sensor has shown very stable response at 350 degrees C and followed a very good behavior and showed 60% response in 50 ppb HCHO concentration at 350 degrees C operating temperatures.

Antitumor activity of peptide amphiphile nanofiber-encapsulated camptothecin.

Self-assembling peptide amphiphile (PA) nanofibers were used to encapsulate camptothecin (CPT), a naturally occurring hydrophobic chemotherapy agent, using a solvent evaporation technique. Encapsulation by PA nanofibers was found to improve the aqueous solubility of the CPT molecule by more than 50-fold. PAs self-assembled into nanofibers in the presence of CPT as demonstrated by transmission electron microscopy. Small-angle X-ray scattering results suggest a slight increase in diameter of the nanofiber to accommodate the hydrophobic cargo. In vitro studies using human breast cancer cells show an enhancement in antitumor activity of the CPT when encapsulated by the PA nanofibers. In addition, using a mouse orthotopic model of human breast cancer, treatment with PA nanofiber-encapsulated CPT inhibited tumor growth. These results highlight the potential of this model PA system to be adapted for delivery of hydrophobic therapies to treat a variety of diseases including cancer.

Microvalves based on ionic polymer-metal composites for microfluidic application.

Simple and highly efficient microvalve systems based on an ionic polymer-metal composite (IPMC) diaphragm actuator have been developed. The microvalve system that was fabricated in this work operates when open and close voltage is applied, due to the phenomena of lithium ion flux and the subsequent electro-osmotic drag of water to the cathode. IPMC was prepared by compositing with platinum nanoparticles on both sides of Nafion thin film. SEM images of the IPMC showed the high density and uniform size distribution of the Pt nanoparticles in the interpenetrating layer to ensure the proper performance of an IPMC actuator. The displacement of the IPMC for the microvalve was measured with a laser displacement meter. The application of open and close voltage made the operation of the valve faster. The fluorescence images of the flow in the fabricated IPMC-based microvalve system showed the successful operation of flow control in the microfluidic channel. The IPMC-based microvalve system shows a potential of IPMC for application as an actuator in microfluidic systems.

Light-induced self-assembly of nanofibers inside liposomes.

Spatially confined self-assembly of peptide amphiphile nanofibers inside liposomes is triggered by light.

Anion-directed self-organization of thermotropic liquid crystalline materials containing a guanidinium moiety.

New wedge-shaped thermotropic liquid crystalline materials containing a guanidinium moiety at the apex organize into various supramolecular structures such as hexagonal columnar, rectangular columnar and Pm3n cubic mesophases depending on anions illustrating guest-directed self-organization in mesophases.

Vesicle formed by amphiphilc cucurbit[6]uril: versatile, noncovalent modification of the vesicle surface, and multivalent binding of sugar-decorated vesicles to lectin.

We report a novel vesicle formed by an amphiphilic CB[6] derivative, the surface of which can be easily modified via host-guest interactions by taking advantage of molecular cavities, readily accessible at the vesicle surface, and their strong affinity toward polyamines. Amphiphilic CB[6] derivative 1 synthesized by reaction between (allyloxy)12CB[6] and 2-[2-(2-methoxyethoxy)ethoxy]ethanethiol affords a vesicle that has been characterized by TEM, light scattering, and fluorescent dye entrapment experiments. Treatment of vesicle 1 with FITC (fluorescein isothiocyanate)-spermine conjugate ligand 2, in which spermine serves as a binding motif to CB[6] and FITC as a fluorescent tag, produced a surface-modified vesicle, which can be easily visualized by a confocal microscope. This result provides us with a new noncovalent, modular approach to the modification of vesicle surfaces. By treating the vesicle derived from the amphiphilic CB[6] with a tag-attached polyamine, we can easily decorate the surface of the vesicle with the tag. Sugar-decorated vesicles were prepared by this noncovalent method, and their interactions with concanavalin A (ConA) were studied. The binding constant of the vesicle decorated with mannose-spermidine conjugate 3 to ConA was measured to be approximately 3 x 104 M-1, which is almost 3 orders of magnitude higher than that of free ligand 3 to ConA (K = approximately 50 M-1). On the other hand, the binding constant of the vesicle coated with galactose-spermidine conjugate 4 to ConA was too small to be measured. These results illustrate the specific and multivalent interactions between the mannose-decorated vesicle and ConA. The ability for facile surface modification suggests many practical applications, including its use in targeted drug delivery and immunization.

Synthesis of a Nanoporous Polymer with Hexagonal Channels from Supramolecular Discotic Liquid Crystals.

Hydrogen-bonding interactions between a benzotri(imidazole) derivative and a polymerizable alkoxybenzoic acid result in the formation of a supramolecular hexagonal columnar liquid crystal. Light-induced polymerization followed by removal of the benzotri(imidazole) core produces a porous polymer with hexagonal channels.