Joonwon Bae

Cure Behavior of the Liquid-Crystalline Epoxy/Carbon Nanotube System and the Effect of Surface Treatment of Carbon Fillers on Cure Reaction

The FT-IR spectra of carbon nanotubes (CN) and oxidated carbon nanotubes were obtained using diffuse reflection Fourier-transform infrared (DRIFT) spectroscopy. The cure behavior of the liquid-crystalline epoxy (LCE)/CN and the LCE/carbon black (CB) systems were investigated. The effect of surface treatment of the carbon nanotube on the cure behavior in the LCE/CN system was investigated with differential scanning calorimetry (DSC), and was compared with those of the CB. The heat of cure in the LCE/CN system was higher than that in the LCE/CB system. The activation energy was dependent on the concentration of the curing agent. The activation energies for the cure reaction were decreased as a result of surface treatment of carbon materials. It was possible to promote the curing reaction by the surface treatment of the carbon nanotube without decreasing the heat of cure. The isothermal kinetic parameters were obtained from the Kamal equation. TEM images of carbon nanotube: carbon nanotube bundle.

High-Performance Flexible Graphene Aptasensor for Mercury Detection in Mussels

Mercury (Hg) is highly toxic but has been widely used for numerous domestic applications, including thermometers and batteries, for decades, which has led to fatal outcomes due to its accumulation in the human body. Although many types of mercury sensors have been developed to protect the users from Hg, few methodologies exist to analyze Hg(2+) ions in low concentrations in real world samples. Herein, we describe the fabrication and characterization of liquid-ion gated field-effect transistor (FET)-type flexible graphene aptasensor with high sensitivity and selectivity for Hg. The field-induced responses from the graphene aptasensor had excellent sensing performance, and Hg(2+) ions with very low concentration of 10 pM could be detected, which is 2-3 orders of magnitude more sensitive than previously reported mercury sensors using electrochemical systems. Moreover, the aptasensor showed a highly specific response to Hg(2+) ions in mixed solutions. The flexible graphene aptasensor showed a very rapid response, providing a signal in less than 1 s when the Hg(2+) ion concentration was altered. Specificity to Hg(2+) ions was demonstrated in real world samples (in this case samples derived from mussels). The aptasensor was fabricated by transferring chemical vapor deposition (CVD)-grown graphene onto a transparent flexible substrate, and the structure displayed excellent mechanical durability and flexiblility. This graphene-based aptasensor has potential for detecting Hg exposure in human and in the environment.

A study on the effect of surface treatment of carbon nanotubes for liquid crystalline epoxide–carbon nanotube composites

Chemical surface oxidation of carbon nanotubes was employed to modify the interfaces between liquid crystalline epoxide (LCE) molecules and carbon nanotubes (CNs). Polar functional groups are formed on the surfaces of the carbon nanotubes as a result of the treatment. The thermotropic behavior of the nematic liquid crystalline (LC) phase in liquid crystalline epoxide–carbon nanotube (LCE–CN) composites has been examined using polarized optical microscopy. The LC phase in the LCE–surface oxidized CN composite evolves at a lower temperature compared to that for LCE–CN, due to polar interactions. The mechanical properties of LCE–CN composites tend to increase with increasing CN content. The electrical conductivity of LCE–CN composites was found to increases dramatically compared to that of pristine LCE resin, up to 5 wt% CN loading, and then increase linearly with increasing CN content at high CN loadings. An investigation of the thermal properties of LCE–CNs in relation to the surface treatment of CNs was also undertaken. Surface oxidation of CNs was found to improve the mechanical durability and thermal stability of LCE–CN composites.

Large‐Scale Graphene Micropattern Nano‐biohybrids: High‐Performance Transducers for FET‐Type Flexible Fluidic HIV Immunoassays

Large-scale FET-type graphene micropattern (GM) nano-biohybrid-based immunosensor (GMNS) is fabricated in a controlled fashion to detect human immunodeficiency virus 2 antibody. Flexible GMNS shows a highly sensitive response and excellent mechanical bendability. The flexible GMNS in fluidic systems also has a stable response. This is the first experimental demonstration of a large-scale flexible fluidic FET-type immunoassay based on GM nano-biohybrids.

An Ultrasensitive, Selective, Multiplexed Superbioelectronic Nose That Mimics the Human Sense of Smell

Human sensory-mimicking systems, such as electronic brains, tongues, skin, and ears, have been promoted for use in improving social welfare. However, no significant achievements have been made in mimicking the human nose due to the complexity of olfactory sensory neurons. Combinational coding of human olfactory receptors (hORs) is essential for odorant discrimination in mixtures, and the development of hOR-combined multiplexed systems has progressed slowly. Here, we report the first demonstration of an artificial multiplexed superbioelectronic nose (MSB-nose) that mimics the human olfactory sensory system, leading to high-performance odorant discriminatory ability in mixtures. Specifically, portable MSB-noses were constructed using highly uniform graphene micropatterns (GMs) that were conjugated with two different hORs, which were employed as transducers in a liquid-ion gated field-effect transistor (FET). Field-induced signals from the MSB-nose were monitored and provided high sensitivity and selectivity toward target odorants (minimum detectable level: 0.1 fM). More importantly, the potential of the MSB-nose as a tool to encode hOR combinations was demonstrated using principal component analysis.

A new polymeric binder for silicon-carbon nanotube composites in lithium ion battery

AbstractWe introduced polyethyleneimine (PEI) as a new binder for silicon (Si)-carbon nanotube (CNT) anode materials in lithium ion batteries (LIBs). The PEI binder was chosen to enhance the binding of electrode material containing Si-CNT nanocomposites through the formation of a PEI thin layer on the surfaces of CNTs. It was expected that the spontaneous electrostatic interactions between weakly charged PEI molecules with CNT surfaces could promote the binding performance. In other words, the formation of solid-electrolyte interface (SEI) could be suppressed owing to the effect of dominant electrostatic interactions between PEIs and CNTs. Zeta potential analyses demonstrated the real presence of electrostatic interactions between PEIs and CNTs. Accordingly, lithium battery half-cell tests showed that improved capacity retention behavior was observed in the sample with PEI than that with polyvinyldifluoride (PVDF) binder. Remarkably, for the case of Si-CNT anode materials prepared without or with relatively less amount of CNT, a higher reduction in capacity was observed with PEI binder than with PVDF. An additional advantage of the incorporation of PEI binder is an increase of initial coulombic efficiency approximately 5%∼10%. Consequently, all these findings support that PEI is highly desirable as an alternative binder for electrode materials containing CNT.

Carboxylic Acid-Functionalized Conducting-Polymer Nanotubes as Highly Sensitive Nerve-Agent Chemiresistors.

Organophosphates are powerful inhibitors of acetylcholinesterase, which is critical to nerve function. Despite continuous research for detecting the highly toxic organophosphates, a new and improved methodology is still needed. Herein we demonstrate simple-to-fabricate chemiresistive gas sensors using conducting-polymer polypyrrole (PPy) nanotube transducers, which are chemically specific and capable of recognizing sub-ppb concentrations (ca. 0.5 ppb) of dimethyl methylphosphonate (DMMP), a simulant of nerve agent sarin. Interestingly, the introduction of carboxylic groups on the surface of PPy nanotube transistors resulted in enhanced sensitivity to DMMP via intermolecular hydrogen bonding. Furthermore, it was found that the sensitivity of the nanotube transducer depended on the degree of the carboxylic group introduced. Finally, a sensor array composed of 5 different transducers including the carboxylated nanotubes exhibited excellent selectivity to DMMP in 16 vapor species.

Germline mutations and genotype–phenotype correlations in patients with apparently sporadic pheochromocytoma/paraganglioma in Korea

The aim of our study was to assess the frequency of germline mutations and develop the genetic testing strategy in patients with apparently sporadic pheochromocytoma/paraganglioma (PPGL) in Korea. We included 53 patients diagnosed with non‐syndromic PPGL without a family history of PPGLs in three referral centers from 2004 to 2011. Succinate dehydrogenase complex B (SDHB), SDHD, Von Hippel–Lindau (VHL), and rearranged during transfection (RET) genes were examined by direct sequencing and multiple ligation‐dependent probe amplification. The study patients were composed of 26 men and 27 women, and mean age was 50.1 ± 13.5 years. The frequency of germline mutations was 13.2% (7/53): RET (n = 2), VHL (n = 1), SDHB (n = 2), and SDHD (n = 2). Six of seven mutation carriers were diagnosed before the age of 50. One of two patients harboring an SDHB mutation had malignant PPGLs. One patient with multifocal head and neck paraganglioma (PGL) and pheochromocytoma (PHEO) carried a SDHD mutation. The carriers of germline mutations in patients with apparently sporadic PPGL were 13.2% in our study. We recommend genetic testing in patients below 50 years and SDHD genetic testing in patients with multifocal PPGLs. In malignant PPGLs, SDHB genetic testing may be performed.

Dopamine Receptor D1 Agonism and Antagonism Using a Field-Effect Transistor Assay

The field-effect transistor (FET) has been used in the development of diagnostic tools for several decades, leading to high-performance biosensors. Therefore, the FET platform can provide the foundation for the next generation of analytical methods. A major role of G-protein-coupled receptors (GPCRs) is in the transfer of external signals into the cell and promoting human body functions; thus, their principle application is in the screening of new drugs. The research community uses efficient systems to screen potential GPCR drugs; nevertheless, the need to develop GPCR-conjugated analytical devices remains for next-generation new drug screening. In this study, we proposed an approach for studying receptor agonism and antagonism by combining the roles of FETs and GPCRs in a dopamine receptor D1 (DRD1)-conjugated FET system, which is a suitable substitute for conventional cell-based receptor assays. DRD1 was reconstituted and purified to mimic native binding pockets that have highly discriminative interactions with DRD1 agonists/antagonists. The real-time responses from the DRD1-nanohybrid FET were highly sensitive and selective for dopamine agonists/antagonists, and their maximal response levels were clearly different depending on their DRD1 affinities. Moreover, the equilibrium constants (K) were estimated by fitting the response levels. Each K value indicates the variation in the affinity between DRD1 and the agonists/antagonists; a greater K value corresponds to a stronger DRD1 affinity in agonism, whereas a lower K value in antagonism indicates a stronger dopamine-blocking effect.

A unique embossed carbon layer from induced domain alignment in a block copolymer thin film under an electric field

A unique embossed carbon surface with regionally heterogeneous properties is constructed via carbonization of a polyacrylonitrile-b-poly(methyl methacrylate) (PAN-b-PMMA) block copolymer thin film precursor self-assembled under an external electric field. The PAN-b-PMMA block copolymer generates a thin surface having microdomains with alternating PAN-PMMA compositions different from that of the matrix when the microdomain alignment is induced under an electric field due to the difference in dielectric susceptibilities between two blocks.