Nanobrick Wall Multilayer Thin Films with High Dielectric Breakdown Strength.

Current thermally conductive and electrically insulating insulation systems are struggling to meet the needs of modern electronics due to increasing heat generation and power densities. Little research has focused on creating insulation systems that excel at both dissipating heat and withstanding high voltages (i.e., have both high thermal conductivity and a high breakdown strength). Herein, a polyelectrolyte-based multilayer nanocomposite is demonstrated to be a thermally conductive high-voltage insulation. Through inclusion of both boehmite and vermiculite clay, the breakdown strength of the nanocomposite was increased by ≈115%. It was also found that this unique nanocomposite has an increase in its breakdown strength, modulus, and hydrophobicity when exposed to elevated temperatures. This readily scalable insulation exhibits a remarkable combination of breakdown strength (250 kV/mm) and thermal conductivity (0.16 W m-1 K-1) for a polyelectrolyte-based nanocomposite. This dual clay insulation is a step toward meeting the needs of the next generation of high-performance insulation systems.

Significant Elevation in Potassium Concentration Surrounding Stimulated Excitable Cells Revealed by an Aptamer-Modified Nanowire Transistor.

Recording ion fluctuations surrounding biological cells with a nanoelectronic device offers seamless integration of nanotechnology into living organisms and is essential for understanding cellular activities. The concentration of potassium ion in the extracellular fluid (CK+ex) is a critical determinant of cell membrane potential and must be maintained within an appropriate range. Alteration in CK+ex can affect neuronal excitability, induce heart arrhythmias, and even trigger seizure-like reactions in the brain. Therefore, monitoring local fluctuations in real time provides an early diagnosis of the occurrence of the K+-induced pathophysiological responses. Here, we modified the surface of a silicon nanowire field-effect transistor (SiNW-FET) with K+-specific DNA-aptamers (AptK+) to monitor the real-time variations of CK+ex in primary cultured rat embryonic cortical neurons or human embryonic stem cell-derived cardiomyocytes. The binding affinity of AptK+ to K+, determined by measuring the dissociation constant of the AptK+-K+ complex (Kd = 10.1 ± 0.9 mM), is at least 38-fold higher than other ions (e.g., Na+, Ca2+, and Mg2+). By placing cultured cortical neurons over an AptK+/SiNW-FET device, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) stimulation raised the CK+ex dose-dependently to 16 mM when AMPA concentration was >10 µM; this elevation could be significantly suppressed by an AMPA receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione. Likewise, the stimulation of isoproterenol to cardiomyocytes raised the CK+ex to 6-8 mM, with a concomitant increase in the beating rate. This study utilizing a robust nanobiosensor to detect real-time ion fluctuations surrounding excitable cells underlies the importance of ion homeostasis and offers the feasibility of developing an implant device for real-time monitoring.

Super Gas Barrier of a Polyelectrolyte/Clay Coacervate Thin Film.

Transparent polymeric thin films with high oxygen barrier are important for extending the shelf life of food and protecting flexible organic electronic devices. Polyelectrolyte/clay multilayer nanocoatings are shown to exhibit super gas barrier performance, but the layer-by-layer assembly process requires numerous deposition steps. In an effort to more quickly fabricate this type of barrier, a polyelectrolyte/clay coacervate composed of branched polyethyleneimine (PEI), poly(acrylic acid) (PAA), and kaolinite (KAO) clay is prepared and deposited in a single step, followed by humidity and thermal post-treatments. When deposited onto a 179 µm poly(ethylene terephthalate) (PET) film, a 4 µm coacervate coating reduces the oxygen transmission rate (OTR) by more than three orders of magnitude, while maintaining high transparency. This single-step deposition process uses only low-cost, water-based components and ambient conditions, which can be used to for sensitive food and electronics packaging.

Environmentally Benign and Self-Extinguishing Multilayer Nanocoating for Protection of Flammable Foam.

Most current flame-retardant nanocoatings for flexible polyurethane foam (PUF) consist of passive barriers, such as clay, graphene oxide, or metal hydroxide. In an effort to develop a polymeric and environmentally benign nanocoating for PUF, positively charged chitosan (CH) and anionic sodium hexametaphosphate (PSP) were deposited using layer-by-layer (LbL) assembly. Only six bilayers of CH/PSP film can withstand flame penetration during exposure to a butane torch (∼1400 °C) for 10 s and stop flame spread on the foam. Additionally, cone calorimetry reveals that the fire growth rate, peak heat release rate, and maximum average rate of heat emission are reduced by 55, 43, and 38%, respectively, compared with uncoated foam. This multilayer thin film quickly dehydrates to form an intumescent charred exoskeleton on the surface of the open-celled structure of polyurethane, inhibiting heat transfer and completely eliminating melt dripping. This entirely polymeric nanocoating provides a safe and effective alternative for reducing the fire hazard of polyurethane foam that is widely used for cushioning and insulation.

Lipid-Modified Graphene-Transistor Biosensor for Monitoring Amyloid-ß Aggregation.

A graphene field-effect transistor (G-FET) with the spacious planar graphene surface can provide a large-area interface with cell membranes to serve as a platform for the study of cell membrane-related protein interactions. In this study, a G-FET device paved with a supported lipid bilayer (referred to as SLB/G-FET) was first used to monitor the catalytic hydrolysis of the SLB by phospholipase D. With excellent detection sensitivity, this G-FET was also modified with a ganglioside GM1-enriched SLB (GM1-SLB/G-FET) to detect cholera toxin B. Finally, the GM1-SLB/G-FET was employed to monitor amyloid-beta 40 (Aß40) aggregation. In the early nucleation stage of Aß40 aggregation, while no fluorescence was detectable with traditional thioflavin T (ThT) assay, the prominent electrical signals probed by GM1-SLB/G-FET demonstrate that the G-FET detection is more sensitive than the ThT assay. The comprehensive kinetic information during the Aß40 aggregation could be collected with a GM1-SLB/G-FET, especially covering the kinetics involved in the early stage of Aß40 aggregation. These experimental results suggest that SLB/G-FETs hold great potential as a powerful biomimetic sensor for versatile investigations of membrane-related protein functions and interaction kinetics.

One-Step Synthesis of Antioxidative Graphene-Wrapped Copper Nanoparticles on Flexible Substrates for Electronic and Electrocatalytic Applications.

In this study, we report a novel, one-step synthesis method to fabricate multilayer graphene (MLG)-wrapped copper nanoparticles (CuNPs) directly on various substrates (e.g., polyimide film (PI), carbon cloth (CC), or Si wafer (Si)). The electrical resistivities of the pristine MLG-CuNPs/PI and MLG-CuNPs/Si were measured 1.7 × 10-6 and 1.4 × 10-6 Ω·m, respectively, of which both values are ∼100-fold lower than earlier reports. The MLG shell could remarkably prevent the Cu nanocore from serious damages after MLG-CuNPs being exposed to various harsh conditions. Both MLG-CuNPs/PI and MLG-CuNPs/Si retained almost their conductivities after ambient annealing at 150 °C. Furthermore, the flexible MLG-CuNPs/PI exhibits excellent mechanical durability after 1000 bending cycles. We also demonstrate that the MLG-CuNPs/PI can be used as promising source-drain electrodes in fabricating flexible graphene-based field-effect transistor (G-FET) devices. Finally, the MLG-CuNPs/CC was shown to possess high performance and durability toward hydrogen evolution reaction (HER).

Catalysis of oxidation of carbon monoxide on supported gold nanoparticle.

Gold used to be considered to have no catalytic activity. In the 1980s, however, Masatake Haruta found that nano-sized gold particles supported by metal oxides can catalyze the oxidation of carbon monoxide. This work examines the oxidation of carbon monoxide (CO) and the adsorption/desorption behaviors on nano-sized gold catalyst at room temperature by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Carbonate, bicarbonate and carboxylate were observed. The effects of various factors (relative humidity, CO gas concentration, and total surface area) on the CO conversion efficiency were studied using the response surface designs in the Experiment Design Method. The results indicate that the conversion efficiency of CO was high when the ratio of CO and O(2) was close to 1:1. The gas concentration is the most important factor, followed by the weight of gold catalyst, followed by relative humidity. An appropriate humidity enhances the catalytic reaction in the long-term.