Ni-rGO Sensor Combined with Human Olfactory Receptor-Embedded Nanodiscs for Detecting Gas-Phase DMMP as a Simulant of Nerve Agents.

Nerve agents are organophosphorus toxic chemicals that can inhibit acetylcholinesterase, leading to paralysis of the nervous system and death. Early detection of nerve agents is important for safety issues. Dimethyl methylphosphonate (DMMP) is widely used as a simulant of nerve agents, and many studies have been conducted using DMMP as a substitute for detecting nerve agents. Despite many studies on sensors for detecting DMMP, they have limitations in sensitivity and selectivity. To overcome these limitations, a nickel-decorated reduced graphene oxide (Ni-rGO) sensor with human olfactory receptor hOR2T7 nanodiscs was utilized to create a bioelectronic nose platform for DMMP gas detection. hOR2T7 was produced and reconstituted into nanodiscs for enhancing the sensor's stability, especially for detection in a gas phase. It could detect DMMP gas selectively and repeatedly at a concentration of 1 ppb. This sensitive and selective bioelectronic nose can be applied as a practical tool for the detection of gaseous chemical warfare agents in military and safety fields.

Enhanced osteogenic differentiation of human mesenchymal stem cells using size-controlled graphene oxide flakes.

Recently, it has been revealed that the physical microenvironment can be translated into cellular mechanosensing to direct human mesenchymal stem cell (hMSC) differentiation. Graphene oxide (GO), a major derivative of graphene, has been regarded as a promising material for stem cell lineage specification due to its biocompatibility and unique physical properties to interact with stem cells. Especially, the lateral size of GO flakes is regarded as the key factor regulating cellular response caused by GO. In this work, GO that had been mechanically created and had an average diameter of 0.9, 1.1, and 1.7 m was produced using a ball-mill process. When size-controlled GO flakes were applied to hMSCs, osteogenic differentiation was enhanced by GO with a specific average diameter of 1.7 µm. It was confirmed that osteogenic differentiation was increased due to the enhanced expression of focal adhesion and the development of focal adhesion subordinate signals via extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase (MEK) pathway. These results suggest that size-controlled GO flakes could be efficient materials for promoting osteogenesis of hMSCs. Results of this study could also improve our understanding of the correlation between hMSCs and cellular responses to GO.

Optorheological Characteristics of Photosynthetic Bacterium Suspension.

Understanding the rheological behavior of materials is of great importance in science. Here, we report a microscopic foundation for optorheology by manipulating the rheological feature through light. A new phenomenon is observed in the photosynthetic bacterial suspension, that the fluid viscosity changes by light-induced electrons. Type IV pili of photosynthetic bacteria is found, and it allows the electron to transport through the exterior of cells and changes the surface potential of cells, which causes an adjustment in the spatial arrangement of cells in the suspension. When an external electric field is applied, the electric dipole of the cells is induced and their dispersion is changed. The rheological properties are measured to evaluate the internal structure of the suspension depending on the light. The photoelectrons enhance the dispersion of the photosynthetic bacteria in the solution, thus leading to a significant increment in the viscosity. We envision that this discovery will provide new applications to the interface of optics, bioengineering, and rheology.

Comparative Studies on Crystallinity, Thermal and Mechanical Properties of Polyketone Grown on Plasma Treated CVD Graphene.

In this work, we report a facile way to control crystalline structures of polyketone (PK) films by combining plasma surface treatment with chemical vapor deposition (CVD) technique. The crystalline structure of PKs grown on plasma-treated graphene and the resulting thermal and mechanical properties were systematically discussed. Every graphene sheet used in this work was produced by CVD method and the production of PKs having different crystallinity were performed on the O2- and N2-doped graphene sheets. It was evident that the CVD-grown graphene sheets acted as the nucleating agents for promoting the crystallization of ß-form PK, while suppressing the growth of α-form PK crystals. Regardless of the increase in surface roughness of graphene, surface functionality of the CVD-grown graphene was found to be an important factor in determining the crystalline structure of PK. N2 plasma treatment of the CVD-grown graphene promoted growth of the ß-form PK, whereas the O2 plasma treatment of CVD graphene led to transformation of the unoriented ß-form PK into the oriented α-form PK. Thus, the resulting thermal and mechanical properties of the PKs were highly dependent on the surface functionality of the CVD graphene. The method of controlling crystalline structure of the PKs suggested in this study, is expected to be very effective in realizing the PK with good processability, heat resistance and mechanical properties.

Ruthenium Decorated Polypyrrole Nanoparticles for Highly Sensitive Hydrogen Gas Sensors Using Component Ratio and Protonation Control.

Despite being highly flammable at lower concentrations and causing suffocation at higher concentrations, hydrogen gas continues to play an important role in various industrial processes. Therefore, an appropriate monitoring system is crucial for processes that use hydrogen. In this study, we found a nanocomposite comprising of ruthenium nanoclusters decorated on carboxyl polypyrrole nanoparticles (Ru_CPPy) to be successful in detecting hydrogen gas through a simple sonochemistry method. We found that the morphology and density control of the ruthenium component increased the active surface area to the target analyte (hydrogen molecule). Carboxyl polypyrrole (CPPy) in the nanocomposite was protonated to increase the charge transfer rate during gas detection. This material-based sensor electrode was highly sensitive (down to 0.5 ppm) toward hydrogen gas and had a fast response and recovery time under ambient conditions. The sensing ability of the electrode was maintained up to 15 days without structure deformations.

Facile Synthesis of Co3O4-Incorporated Multichannel Carbon Nanofibers for Electrochemical Applications.

Considering their superior electrochemical performances, extensive studies have been carried out on composite nanomaterials based on porous carbon nanofibers. However, the introduction of inorganic components into a porous structure is complex and has a low yield. In this study, we propose a simple synthesis of cobalt-oxide-incorporated multichannel carbon nanofibers (P-Co-MCNFs) as electrode materials for electrochemical applications. The cobalt oxide component is directly formed in the carbon structure by a simple oxygen plasma exposure of the phase-separated polymer nanofibers. P-Co-MCNF displays high specific capacitance (815 F g-1 at 2.0 A g-1), rate capability (821 F g-1 at 1 A g-1 and 786 F g-1 at 20 A g-1), and cycle stability (92.1% for 5000 cycles) as a supercapacitor electrode. Moreover, excellent sensitivity (down to 1 nM) and selectivity to the glucose molecule is demonstrated for nonenzyme sensor applications.

Aptamer-Functionalized Three-Dimensional Carbon Nanowebs for Ultrasensitive and Free-Standing PDGF Biosensor.

Research on flexible biosensors is mostly focused on their use in obtaining information on physical signals (such as temperature, heart rate, pH, and intraocular pressure). Consequently, there are hardly any studies on using flexible electronics for detecting biomolecules and biomarkers that cause diseases. In this study, we propose a flexible, three-dimensional carbon nanoweb (3DCNW)-based aptamer sensor to detect the platelet-induced growth factor (PDGF), which is an oncogenic biomarker. As a template for the 3D structure, poly(acrylonitrile) (PAN) nanowebs were synthesized using a facile electrospinning process. The PAN nanowebs were then subjected to chemical vapor deposition with copper powder. This was followed by Cu etching to generate carbon protrusions on the web surface. As an active site, PDGF-B binding aptamer was introduced on the 3DCNW surface to form biosensor electrodes. The 3DCNW-based aptasensor exhibited excellent sensitivity (down to 1.78 fM), with high selectivity, reversibility, and stability to PDGF-BB.

Comparative Study on the Formation and Oxidation-Level Control of Three-Dimensional Conductive Nanofilms for Gas Sensor Applications.

Investment in wearable monitoring systems is increasing rapidly for realizing their practical applications, for example, in medical treatment, sports, and security systems. However, existing wearable monitoring systems are designed to measure a real-time physical signal and abnormal conditions rather than harmful environmental characteristics. In this study, a flexible chemical sensor electrode based on a three-dimensional conductive nanofilm (3D CNF) is fabricated via facile polymerization with temperature control. The morphology and chemical state of the 3D CNF are modified via electrochemical doping control to increase the carrier mobility and the active surface area of the sensor electrode. The sensor electrode is highly sensitive (up to 1 ppb), selective, and stable for an analyte (NH3) at room temperature owing to the three-dimensional morphology of polypyrrole and the oxidation-level control.

Peptide hormone sensors using human hormone receptor-carrying nanovesicles and graphene FETs.

Hormones within very low levels regulate and control the activity of specific cells and organs of the human body. Hormone imbalance can cause many diseases. Therefore, hormone detection tools have been developed, particularly over the last decade. Peptide hormones have a short half-life, so it is important to detect them within a short time. In this study, we report two types of peptide hormone sensors using human hormone receptor-carrying nanovesicles and graphene field-effect transistors (FETs). Parathyroid hormone (PTH) and glucagon (GCG) are peptide hormones present in human blood that act as ligands to G protein-coupled receptors (GPCRs). In this paper, the parathyroid hormone receptor (PTHR) and the glucagon receptor (GCGR) were expressed in human embryonic kidney-293 (HEK-293) cells, and were constructed as nanovesicles carrying the respective receptors. They were then immobilized onto graphene-based FETs. The two hormone sensors developed were able to detect each target hormone with high sensitivity (ca. 100 fM of PTH and 1 pM of GCG). Also, the sensors accurately recognized target hormones among different types of peptide hormones. In the development of hormone detection tools, this approach, using human hormone receptor-carrying nanovesicles and graphene FETs, offers the possibility of detecting very low concentrations of hormones in real-time.

Fluorine plasma treatment on carbon-based perovskite solar cells for rapid moisture protection layer formation and performance enhancement.

A fluorine plasma-treated carbon electrode is used in HTM-free perovskite solar cells for high efficiency and moisture resistance. The fluorine-treated device with a champion power conversion efficiency (PCE) of 14.86% is achieved with a highly enhanced FF (FF = 0.69), showing superior long-term stability and excellent moisture penetration suppression.

Ultrasensitive, Selective, and Highly Stable Bioelectronic Nose That Detects the Liquid and Gaseous Cadaverine.

Field-effect transistor (FET) devices based on conductive nanomaterials have been used to develop biosensors. However, development of FET-based biosensors that allow efficient stability, especially in the gas phase, for obtaining reliable and reproducible responses remains a challenge. In this study, we developed a nanodisc (ND)-functionalized bioelectronic nose (NBN) based on a nickel (Ni)-decorated carboxylated polypyrrole nanoparticle (cPPyNP)-FET that offers the detection of liquid and gaseous cadaverine (CV). The TAAR13c, specifically binding to CV, which is an indicator of food spoilage, was successfully constructed in NDs. The NBN was fabricated by the oriented assembly of TAAR13c-embedded NDs (T13NDs) onto the transistor with Ni/cPPyNPs. The NBN showed high performance in selectivity and sensitivity for the detection of CV, with excellent stability in both aqueous and gas phases. Moreover, the NBN allowed efficient measurement of corrupted real-food samples. It demonstrates the ND-based device can allow the practical biosensor that provides high stability in the gas phase.

Highly porous structured polyaniline nanocomposites for scalable and flexible high-performance supercapacitors.

Recently, flexible energy devices have been used to power up portable electronics such as E-skins, smart clothes, and bendable displays. However, the usage of rigid and inactive components in electrode materials limits the application in flexible energy devices. Here, we report a novel method to fabricate porous polyaniline composites (Pt_CPPy/PANI:CSA) using Pt decorated carboxyl polypyrrole nanoparticles (Pt_CPPyNPs) as a nucleating agent for electrodes of supercapacitors. The specific capacitance and electrical conductivity of the Pt_CPPy/PANI:CSA film are 325.0 F g-1 and 814 S cm-1, respectively, which are much higher than those of the pristine PANI:CSA film. Furthermore, the porous PANI:CSA composites exhibit excellent rate capability and cycling stability as the pores in the PANI structure enhance the active surface area between PANI and the ions of the electrolytes. This unique fabrication technique is an effective approach for preparing large scale highly porous polyaniline nanomaterials for diverse electrochemical applications.

Highly Crystalline Perovskite-Based Photovoltaics via Two-Dimensional Liquid Cage Annealing Strategy.

Rendering a high crystalline perovskite film is integral to achieve superior performance of perovskite solar cells (PSCs). Here, we established a two-dimensional liquid cage annealing system, a unique methodology for remarkable enhancement in perovskite crystallinity. During thermal annealing for crystallization, wet-perovskite films were suffocated by perfluorodecalin with distinctively low polarity, nontoxic, and chemically inert characteristics. This annealing strategy facilitated enlargement of perovskite grain and diminution in the number of trap states. The simulation results, annealing time, and temperature experiments supported that the prolonged diffusion length of precursor ions attributed to the increase of perovskite grains. Consequently, without any complicated handling, the performance of perovskite photovoltaics was remarkably improved, and the monolithic grains which directly connected the lower and upper electrode attenuated hysteresis.

Fabrication of N-doped multidimensional carbon nanofibers for high-performance cortisol biosensors.

Cortisol is an hormone that regulates blood pressure, glucose levels and carbohydrate metabolism in humans. Abnormal secretion of cortisol can cause various symptoms closely linked to psychological and physical health. In this study, high-performance field-effect transistor (FET)-based biosensors for cortisol detection were fabricated from N-doped multidimensional carbon nanofibers. Nanofiber morphology was controlled by tailoring the pressure conditions during vapor deposition polymerization (VDP). Thereafter, conductive channels of FET were completed by thermal annealing, acid treatment, and antibody attachment. Changes associated with chemical processes were characterized by various instruments. The resulting transducers exhibited a rapid response toward cortisol molecules with accurate selectivity, stable reusability, and high sensitivity. Minimum detection level were as low as 100 aM with a wide linear detection range of 100 aM to 10 nM due to the large surface area of the transducer and a correspondingly high number of antibody labels. The response and applicability of these cortisol biosensors were also assessed using saliva as a test matrix.

Activation of Haa1 and War1 transcription factors by differential binding of weak acid anions in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, Haa1 and War1 transcription factors are involved in cellular adaptation against hydrophilic weak acids and lipophilic weak acids, respectively. However, it is unclear how these transcription factors are differentially activated depending on the identity of the weak acid. Using a field-effect transistor (FET)-type biosensor based on carbon nanofibers, in the present study we demonstrate that Haa1 and War1 directly bind to various weak acid anions with different affinities. Haa1 is most sensitive to acetate, followed by lactate, whereas War1 is most sensitive to benzoate, followed by sorbate, reflecting their differential activation during weak acid stresses. We show that DNA binding by Haa1 is induced in the presence of acetic acid and that the N-terminal Zn-binding domain is essential for this activity. Acetate binds to the N-terminal 150-residue region, and the transcriptional activation domain is located between amino acid residues 230 and 483. Our data suggest that acetate binding converts an inactive Haa1 to the active form, which is capable of DNA binding and transcriptional activation.

Conducting Nanomaterial Sensor Using Natural Receptors.

One of the recently emerging topics in biotechnology is natural receptors including G protein-coupled receptors, ligand-gated ion channels, enzyme-linked receptors, and intracellular receptors, due to their molecular specificity. These receptors, other than intracellular receptors, which are membrane proteins expressed on the cell membrane, can detect extracellular stimuli. Many researchers have utilized cells with natural receptors embedded in the cellular membrane for human sense-mimicking platforms based on electrochemical impedance spectroscopy, quartz crystal microbalances, surface plasmon resonance, and surface acoustic waves. In addition, integration of conducting nanomaterials and natural receptors allows highly sensitive and selective responses toward target molecules, enabling, for example, nanobioelectronic noses for odorants, nanobioelectronic tongues for tastants, and G-protein-coupled receptor sensors for hormones, dopamine, cadaverine, geosmin, trimethylamine, etc. Moreover, as a part of nanobioelectronic sensors, natural receptors can be produced in various forms, such as peptides, proteins, nanovesicles, and nanodiscs, and each sensor can provide an ultralow limit of detection. In this Review, we discuss biosensors with natural receptors and then especially focus on natural receptor-conjugated conducting nanomaterial sensors. To provide a fundamental understanding, the sections encompass (1) the fabrication of conducting nanomaterials, (2) the production of natural receptors, (3) the characteristics of natural receptors, (4) the technology for immobilizing both components, and (5) their sensing applications. Finally, perspective is given on a new development in the use of natural receptors in a wide range of industries, such as food, cosmetics, and healthcare. In addition, artificial olfactory codes will be characterized by signal processing in the near future, leading to human olfactory standardization.

Synthesis and Electroresponse Activity of Porous Polypyrrole/Silica-Titania Core/Shell Nanoparticles.

Inverted conducting polymer/metal oxide core/shell structured pPPy/SiO2-TiO2 nanoparticles were prepared as electrorheological (ER) materials using sequential experimental methods. The core was synthesized via the low-temperature self-assembly of PPy and SiO2 materials, and the outer TiO2 shell was easily coated onto the core part using a sol-gel method and a titanium isopropoxide precursor. Sonication-mediated etching and redeposition were employed to etch out SiO2 portions from the core part to blend with TiO2 shells. Each step in nanoparticle synthesis involved morphological and physical changes to the surface area and porosity, with subsequent changes in the intrinsic properties of the materials. Specifically, the electrical conductivity and dielectric properties were successfully altered. The final pPPy/SiO2-TiO2 nanoparticle configuration was optimized for ER applications, offering low electrical conductivity, high dielectric properties, and increased dispersion stability. pPPy/SiO2-TiO2 nanoparticles exhibited 24.7- and 2.7-fold enhancements in ER performance compared to that of PPy-SiO2 and PPy-SiO2/TiO2 precursor nanoparticles, respectively. The versatile method proposed in this study for the synthesis of inverted conducting polymer/metal oxide core/shell nanoparticles shows great potential for the development of custom-designed ER materials.

Multidimensional Conductive Nanofilm-Based Flexible Aptasensor for Ultrasensitive and Selective HBsAg Detection.

Hepatitis B virus (HBV) infection is a major worldwide health issue causing serious liver diseases, including liver cirrhosis and hepatocellular carcinoma. Monitoring the serum hepatitis B surface antigen (HBsAg) level is pivotal to the diagnosis of HBV infection. In this study, we describe multidimensional conductive nanofilm (MCNF)-based field-effect transistor (FET) aptasensor for HBsAg detection. The MCNF, composed of vertically oriented carboxylic polypyrrole nanowires (CPPyNW) and graphene layer, is formed using electropolymerization of pyrrole on the graphene surface and following acid treatment. The amine-functionalized HBsAg-binding aptamers are then immobilized on the CPPyNW surface through covalent bonding formation (i.e., amide group). The prepared aptasensor presents highly sensitive to HBsAg as low as 10 aM among interfering biomolecules with various deformations. Moreover, the MCNF-based aptasensor has great potential for practical application in the noninvasive real-time diagnosis because of its improved sensing ability to the human serum and artificial saliva.

High-performance bioelectronic tongue using ligand binding domain T1R1 VFT for umami taste detection.

Numerous efforts have been made to measure tastes for various purposes. However, most taste information is still obtained by human sensory evaluation. It is difficult to quantify a degree of taste or establish taste standard. Although artificial taste sensors called electronic tongues utilizing synthetic materials such as polymers, semiconductors, or lipid membranes have been developed, they have limited performance due to their low sensitivity and specificity. Recently, bioelectronic tongues fabricated by integrating human taste receptors and nanomaterial-based sensor platforms have been found to have high performance for measuring tastes with human-like taste perception. However, human umami taste receptor is heterodimeric class C GPCR composed of human taste receptor type 1 member 1 (T1R1) and member 3 (T1R3). Such complicated structure makes it difficult to fabricate bioelectronic tongue. The objective of this study was to develop a protein-based bioelectronic tongue for detecting and discriminating umami taste with human-like performance using umami ligand binding domain called venus flytrap (VFT) domain originating from T1R1 instead of using the whole heterodimeric complex of receptors. Such T1R1 VFT was produced from Escherichia coli (E. coli) with purification and refolding process. It was then immobilized onto graphene-based FET. This bioelectronic tongue for umami taste (BTUT) was able to detect monosodium L-glutamate (MSG) with high sensitivity (ca. 1 nM) and specificity in real-time. The intensity of umami taste was enhanced by inosine monophosphate (IMP) that is very similar to the human taste system. In addition, BTUT allowed efficient reusable property and storage stability. It maintained 90% of normalized signal intensity for five weeks. To develop bioelectronic tongue, this approach using the ligand binding domain of human taste receptor rather than the whole heterodimeric GPCRs has advantages in mass production, reusability, and stability. It also has great potential for various industrial applications such as food, beverage, and pharmaceutical fields.

Fabrication of Uniform Wrinkled Silica Nanoparticles and Their Application to Abrasives in Chemical Mechanical Planarization.

A simple one-pot method is reported for the fabrication of uniform wrinkled silica nanoparticles (WSNs). Rapid cooling of reactants at the appropriate moment during synthesis allowed the separation of nucleation and growth stages, resulting in uniform particles. The factors affecting particle size and interwrinkle distance were also investigated. WSNs with particle sizes of 65-400 nm, interwrinkle distances of 10-33 nm, and surface areas up to 617 m2 g-1 were fabricated. Furthermore, our results demonstrate the advantages of WSNs over comparable nonporous silica nanospheres and fumed silica-based products as an abrasive material in chemical mechanical planarization processes.