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.

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.

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.

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.

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.

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.

Sulfur-Immobilized, Activated Porous Carbon Nanotube Composite Based Cathodes for Lithium-Sulfur Batteries.

Activated highly porous carbon nanotubes are synthesized with a facile dual-nozzle co-electrospinning and a redox process to apply the framework of a sulfur-immobilized composite as a high-performance cathode in lithium-sulfur batteries.

Paintable Carbon-Based Perovskite Solar Cells with Engineered Perovskite/Carbon Interface Using Carbon Nanotubes Dripping Method.

Paintable carbon electrode-based perovskite solar cells (PSCs) are of particular interest due to their material and fabrication process costs, as well as their moisture stability. However, printing the carbon paste on the perovskite layer limits the quality of the interface between the perovskite layer and carbon electrode. Herein, an attempt to enhance the performance of the paintable carbon-based PSCs is made using a modified solvent dripping method that involves dripping of the carbon nanotubes (CNTs), which is dispersed in chlorobenzene solution. This method allows CNTs to penetrate into both the perovskite film and carbon electrode, facilitating fast hole transport between the two layers. Furthermore, this method is results in increased open circuit voltage (Voc ) and fill factor (FF), providing better contact at the perovskite/carbon interfaces. The best devices made with CNT dripping show 13.57% power conversion efficiency and hysteresis-free performance.

Graphene Oxide Wrapped SiO2 /TiO2 Hollow Nanoparticles Loaded with Photosensitizer for Photothermal and Photodynamic Combination Therapy.

Graphene oxide (GO) enwrapped SiO2 /TiO2 hollow nanoparticles (GO-HNP) are synthesized by the Stöber method and used as a nanocarrier for loading protoporphyrin IX (PpIX). The synthesized nanoparticle has high dispersibility and high uniformity in diameter (ca. 50 nm). Furthermore, this nanoparticle shows λ=808 nm laser induced PpIX release properties (photoinduced "on-off" drug-release system). GO-HNP-PpIX is employed for inducing both photothermal therapy (PTT) and photodynamic therapy (PDT). The synergic effect of PTT and PDT exhibits powerful anticancer properties. When cancer cells are treated with GO-HNP-PpIX and irradiated with both visible light and a NIR laser, the cell viability drops dramatically to 2.5 %, which is an anticancer effect approximately 13 times higher than that obtained in a previous study. Moreover, no significant cell damage has been observed under λ=808 nm laser irradiation. The GO-HNP-PpIX system suggests an external stimuli-responsive efficient anticancer treatment effect toward human breast cancer cells.

Solvent diffusion in polymer-embedded hollow nanoparticles studied by in situ small angle X-ray scattering.

In situ time-resolved small-angle X-ray scattering is introduced as a method to monitor the diffusion of a solvent in ceramic hollow nanoparticles (HNPs) supported by a polymer gel scaffold. Changes in the form factor were matched to discrete scattering models. A consecutive reaction kinetic model is used to analyze different stages of solvent diffusion. Rate constants and diffusion coefficients are extracted. By taking the diffusion of low molecular poly(ethylene glycol) in poly(ethylene oxide)-embedded HNPs as a model case, it was found that it took about 0.7 s for the solvent to diffuse through the 6 nm thick shell of HNPs and another 1.2 s to fill the inner cavity, while the diffusion coefficient was of the order of 1018 m2 s-1. The results demonstrate that the method can simultaneously measure solvent penetration into the polymer gel and into embedded sub-100 nm HNPs.

High Performance Flexible Actuator of Urchin-Like ZnO Nanostructure/Polyvinylenefluoride Hybrid Thin Film with Graphene Electrodes for Acoustic Generator and Analyzer.

A bass frequency response enhanced flexible polyvinylidene fluoride (PVDF) based thin film acoustic actuator is successfully fabricated. High concentrations of various zinc oxide (ZnO) is embedded in PVDF matrix, enhancing the ß phase content and the dielectric property of the composite thin film. ZnO acts as a nucleation agent for the crystallization of PVDF. A chemical vapor deposition grown graphene is used as electrodes, enabling high electron mobility for the distortion free acoustic signals. The frequency response of the fabricated acoustic actuator is studied as a function of the film thickness and filler content. The optimized film has a thickness of 80 µm with 30 wt% filler content and shows 72% and 42% frequency response enhancement in bass and midrange compared to the commercial PVDF, respectively. Also, the total harmonic distortion decreases to 82% and 74% in the bass and midrange regions, respectively. Furthermore, the composite film shows a promising potential for microphone applications. Most of all, it is demonstrated that acoustic actuator performance is strongly influenced by degree of PVDF crystalline.

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 Comparative Study on Optical, Electrical, and Mechanical Properties of Conducting Polymer-Based Electrodes.

Transparent, free-standing, conducting polypyrrole (PPy) film is successfully fabricated by a simple method using the spin-coating technique. The free-standing PPy film exhibits high transparency, flexibility, electrical conductivity, and stable mechanical properties because the PPy film is composed of densely packed and highly ordered PPy nanoparticles. This approach provides feasible candidate for applications requiring flexible and conducting materials.

Highly Sensitive and Selective Field-Effect-Transistor NonEnzyme Dopamine Sensors Based on Pt/Conducting Polymer Hybrid Nanoparticles.

Dopamine (DA), as one of catecholamine family of neurotransmitters, is crucially important in humans owing to various critical effects on biometric system such as brine circuitry, neuronal plasticity, organization of stress responses, and control of cardiovascular and renal organizations. Abnormal level of dopamine in the central nervous system causes several neurological diseases, e.g., schizophrenia, Parkinson's disease, and attention deficit hybperactivity disorder (ADHD)/attention deficit disorder (ADD). In this report, we suggest the fabrication of nonenzyme field effect transistor (FET) sensor composed of immobilized Pt particle decorated conducting-polymer (3-carboxylate polypyrrole) nanoparticles (Pt_CPPy) to detect dopamine. The hybrid nanoparticles (NPs) are produced by means of facile chemical reduction of pristine CPPyNP-contained Pt precursor (PtCl4 ) solution. The Pt_CPPys are then immobilized on an amine-functionalized (-NH2 ) interdigitated-array electrode substrate, through the formation of covalent bonds with amine groups (-CONH). The resulting Pt_CPPy-based FET sensors exhibit high sensitivity and selectivity toward DA at unprecedentedly low concentrations (100 × 10(-15) m) and among interfering biomolecules, respectively. Additionally, due to the covalent bonding involved in the immobilization process, a longer lifetime is expected for the FET sensor.

Simultaneous Chemical and Optical Patterning of Polyacrylonitrile Film by Vapor-Based Reaction.

The surface of polyacrylonitrile (PAN) film is treated with ethyleneamines (EDA) in a simple chemical vapor phase reaction. Successful introduction of amine functional groups on the cyano group of PAN backbone is verified by FT-IR and NMR measurements. Further UV-vis and photoluminescence analyses show a red shift of the emission peak after repeated EDA treatment, which might be attributed to the formation of imine conjugation from newly formed carbon-nitrogen bonds on the PAN backbone. Further confocal laser scanning microscopy reveals that selective patterning of EDA on PAN films is possible via local polydimethylsiloxane masking. The results indicate that both chemical and optical patterning on PAN film can be realized via a single reaction and show the potential of this novel methodology in selective patterning.

Polypyrrole nanotube embedded reduced graphene oxide transducer for field-effect transistor-type H2O2 biosensor.

We report a rapid-response and high-sensitivity sensor with specificity toward H2O2 based on a liquid-ion-gated field-effect transistor (FET) using graphene-polypyrrole (PPy) nanotube (NT) composites as the conductive channel. The rGO, PPy, NTs, and nanocomposite materials were characterized using Raman spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). On the basis of these results, a well-organized structure is successfully prepared owing to the specific interactions between the PPy NTs and the rGO sheet. Reliable electrical contacts were developed between the rGO/PPy NTs and the microelectrodes, which remained stable when exposed to the liquid-phase analyte. Liquid-ion-gated FETs composed of these graphene nanocomposites exhibited hole-transport behavior with conductivities higher than those of rGO sheets or PPy NTs. This implies an interaction between the PPy NTs and the rGO layers, which is explained in terms of the PPy NTs forming a bridge between the rGO layers. The FET sensor provided a rapid response in real time and high sensitivity toward H2O2 with a limit of detection of 100 pM. The FET-type biosensing geometry was also highly reproducible and stable in air. Furthermore, the liquid-gated FET-type sensor exhibited specificity toward H2O2 in a mixed solution containing compounds found in biological fluids.

Multifunctional Ag-decorated porous TiO2 nanofibers in dye-sensitized solar cells: efficient light harvesting, light scattering, and electrolyte contact.

Designing the photoanode structure in dye-sensitized solar cells (DSSCs) is vital to realizing enhanced power conversion efficiency (PCE). Herein, novel multifunctional silver-decorated porous titanium dioxide nanofibers (Ag/pTiO2 NFs) made by simple electrospinning, etching, and chemical reduction processes are introduced. The Ag/pTiO2 NFs with a high surface area of 163 m(2) g(-1) provided sufficient dye adsorption for light harvesting. Moreover, the approximately 200 nm diameter and rough surface of the Ag/pTiO2 NFs offered enough light scattering, and the enlarged interpores among the NFs in the photoanode also permitted electrolyte circulation. Ag nanoparticles (NPs) were well dispersed on the surface of the TiO2 NFs, which prevented aggregation of the Ag NPs after calcination. Furthermore, a localized surface plasmon resonance effect by the Ag NPs served to increase the light absorption at visible wavelengths. The surface area and amount of Ag NPs was optimized. The PCE of pTiO2 NF-based DSSCs was 27 % higher (from 6.2 to 7.9 %) than for pure TiO2 NFs, whereas the PCE of Ag/pTiO2 NF-based DSSCs increased by about 12 % (from 7.9 to 8.8 %). Thus, the PCE of the multifunctional pTiO2 NFs was improved by 42 %, that is, from 6.2 to 8.8 %.

SiO(2) /TiO(2) hollow nanoparticles decorated with Ag nanoparticles: enhanced visible light absorption and improved light scattering in dye-sensitized solar cells.

Hollow SiO2 /TiO2 nanoparticles decorated with Ag nanoparticles (NPs) of controlled size (Ag@HNPs) were fabricated in order to enhance visible-light absorption and improve light scattering in dye-sensitized solar cells (DSSCs). They exhibited localized surface plasmon resonance (LSPR) and the LSPR effects were significantly influenced by the size of the Ag NPs. The absorption peak of the LSPR band dramatically increased with increasing Ag NP size. The LSPR of the large Ag NPs mainly increased the light absorption at short wavelengths, whereas the scattering from the SiO2 /TiO2 HNPs improved the light absorption at long wavelengths. This enabled the working electrode to use the full solar spectrum. Furthermore, the SiO2 layer thickness was adjusted to maximize the LSPR from the Ag NPs and avoid corrosion of the Ag NPs by the electrolyte. Importantly, the power conversion efficiency (PCE) increased from 7.1 % with purely TiO2 -based DSSCs to 8.1 % with HNP-based DSSCs, which is an approximately 12 % enhancement and can be attributed to greater light scattering. Furthermore, the PCEs of Ag@HNP-based DSSCs were 11 % higher (8.1 vs. 9.0 %) than the bare-HNP-based DSSCs, which can be attributed to LSPR. Together, the PCE of Ag@HNP-based DSSCs improved by a total of 27 %, from 7.1 to 9.0 %, due to these two effects. This comparative research will offer guidance in the design of multifunctional nanomaterials and the optimization of solar-cell performance.

High-performance Hg(2+) FET-type sensors based on reduced graphene oxide-polyfuran nanohybrids.

A new type of field-effect transistor (FET) sensor, based on reduced graphene oxide (rGO)-polyfuran (PF) nanohybrids, was strategically developed. The sensing transducer exhibited a rapid response (<1 s) and high sensitivity (10 pM) in a liquid-ion-gated FET-type Hg(2+) sensor. Excellent Hg(2+) discrimination in heavy metal mixtures was also monitored in real time.

Conducting polymer-based nanohybrid transducers: a potential route to high sensitivity and selectivity sensors.

The development of novel sensing materials provides good opportunities to realize previously unachievable sensor performance. In this review, conducting polymer-based nanohybrids are highlighted as innovative transducers for high-performance chemical and biological sensing devices. Synthetic strategies of the nanohybrids are categorized into four groups: (1) impregnation, followed by reduction; (2) concurrent redox reactions; (3) electrochemical deposition; (4) seeding approach. Nanocale hybridization of conducting polymers with inorganic components can lead to improved sorption, catalytic reaction and/or transport behavior of the material systems. The nanohybrids have thus been used to detect nerve agents, toxic gases, volatile organic compounds, glucose, dopamine, and DNA. Given further advances in nanohybrids synthesis, it is expected that sensor technology will also evolve, especially in terms of sensitivity and selectivity.