Photoresponse Analysis of All-Inkjet-Printed Single-Walled Carbon Nanotube Thin-Film Transistors for Flexible Light-Insensitive Transparent Circuit Applications.

We report daylight-stable, transparent, and flexible single-walled carbon nanotube thin-film transistors (SWCNT TFTs) using an all-inkjet printing process. Although most of the previous reports classified SWCNT TFTs as photodetectors, we demonstrated that SWCNT films actually show two different types of photoresponses depending on the power levels of light sources. The electrical characteristics of SWCNT TFTs show no significant change under daily illumination conditions such as halogen lamps and sunlight, while under high-power laser illumination, they change as reported in the previous results. In addition, the low-temperature solution process of the SWCNT with its one-dimensional nature allows us to realize highly transparent and flexible TFTs and logic circuits on plastic substrates. Our result will provide new insights into utilizing SWCNT TFTs for light-insensitive transparent and flexible electronic applications.

Inhibitory effects of Streptococcus salivarius K12 on formation of cariogenic biofilm.

Bacground/purpose: Streptococcus salivarius (S. salivarius) K12 is known to be a probiotic bacterium. The purpose of this study was to investigate anti-cariogenic effects of S. salivarius K12 on cariogenic biofilm. Materials and methods: S. salivarius K12 was cultured in M17 broth. The antimicrobial activity of spent culture medium (SCM) against Streptococcus mutans was investigated. S. salivarius K12 was co-cultivated with S. mutans using a membrane insert. When the biofilm was formed using salivary bacteria and S. mutans, the K12 was inoculated every day. The biomass of biofilm was investigated by a confocal laser scanning microscope. Also, bacterial DNA from the biofilm was extracted, and then bacteria proportion was analyzed by quantitative PCR using specific primers. The expression of gtf genes of S. mutans in the biofilm with or without S. salivarius K12 was analyzed by RT-PCR. Results: The SCM of S. salivarius K12 inhibited the growth of S. mutans. Also, S. salivarius K12 reduced S. mutans growth in co-cultivation. The formation of cariogenic biofilm was reduced by adding S. salivarius K12, and the count of S. mutans in the biofilm was also decreased in the presence of S. salivarius K12. gtfB, gtfC, and gtfD expression of S. mutans in the biofilm was reduced in the presence of S. salivarius K12. Conclusion: S. salivarius K12 may inhibit the formation of cariogenic biofilm by interrupting the growth and glucosyltransferase production of S. mutans.

Silent Speech Recognition with Strain Sensors and Deep Learning Analysis of Directional Facial Muscle Movement.

Silent communication based on biosignals from facial muscle requires accurate detection of its directional movement and thus optimally positioning minimum numbers of sensors for higher accuracy of speech recognition with a minimal person-to-person variation. So far, previous approaches based on electromyogram or pressure sensors are ineffective in detecting the directional movement of facial muscles. Therefore, in this study, high-performance strain sensors are used for separately detecting x- and y-axis strain. Directional strain distribution data of facial muscle is obtained by applying three-dimensional digital image correlation. Deep learning analysis is utilized for identifying optimal positions of directional strain sensors. The recognition system with four directional strain sensors conformably attached to the face shows silent vowel recognition with 85.24% accuracy and even 76.95% for completely nonobserved subjects. These results show that detection of the directional strain distribution at the optimal facial points will be the key enabling technology for highly accurate silent speech recognition.

Stretchable PPG sensor with light polarization for physical activity-permissible monitoring.

Skin-attachable sensors, which represent the ultimate form of wearable electronic devices that ensure conformal contact with skin, suffer from motion artifact limitations owing to relative changes in position between the sensor and skin during physical activities. In this study, a polarization-selective structure of a skin-conformable photoplethysmographic (PPG) sensor was developed to decrease the amount of scattered light from the epidermis, which is the main cause of motion artifacts. The motion artifacts were suppressed more than 10-fold in comparison with those of rigid sensors. The developed sensor-with two orthogonal polarizers-facilitated successful PPG signal monitoring during wrist angle movements corresponding to high levels of physical activity, enabling continuous monitoring of daily activities, even while exercising for personal health care.

Virulence of Filifactor alocis lipoteichoic acid on human gingival fibroblast.

OBJECTIVES: The purpose of this study was to investigate virulence of lipoteichoic acid extracted from Filifactor alocis (F. alocis) through comparison of previously known bacterial virulence factors. DESIGN: F. alocis was cultured in columbia media including L-arginine and L-cysteine, and lipoteichoic acid (LTA) from F. alocis was purified using organic solvent and bead extraction. Human gingival fibroblasts (HGFs) were treated with the extracted LTA and other Gram-positive LTA or lipopolysaccharide of other periodontopathogens. The induction of cytokine expression was examined by real-time RT-PCR and ELISA, and the stimulated signaling pathway by the LTA was investigated by immunoblotting and various inhibitors. RESULTS: LTA induced expression of pro-inflammatory cytokines and Matrix-metalloprotein 2. Also, F. alocis LTA induced expression pro-inflammatory cytokines similar to Porphyromonas gingivalis lipopolysaccharide. The LTA activated NF-κB and MAP kinase pathway. Furthermore, the induction of TNF-α, IL-6, IL-8, and MMP-2 expression by F. alocis LTA was reduced by the inhibitor of NF-κB, ERK, JNK, and p38 pathway. CONCLUSIONS: LTA of F. alocis, a bacterium recently detected in periodontal patients, may play an important role in inducing periodontitis by induction of expression of pro-inflammatory cytokines.

Inkjet-Printing-Based Density Profile Engineering of Single-Walled Carbon Nanotube Networks for Conformable High-On/Off-Performance Thin-Film Transistors.

Random networks of single-walled carbon nanotubes (SWCNTs) offer new-form-factor electronics such as transparent, flexible, and intrinsically stretchable devices. However, the long-standing trade-off between carrier mobility and on/off ratio due to the coexistence of metallic and semiconducting nanotubes has limited the performance of SWCNT-random-network-based thin-film transistors (SWCNT TFTs), hindering their practical circuit-level applications. Methods for high-purity separation between metallic and semiconducting nanotubes have been proposed, but they require high cost and energy and are vulnerable to contamination and nanotube shortening, leading to performance degradation. Alternatively, additional structures have been proposed to reduce the off-state current, but they still compromise carrier mobility and suffer from inevitable expansion in device dimensions. Here, we propose a density-modulated SWCNT network using an inkjet-printing method as a facile approach that can achieve superior carrier mobility and a high on/off ratio simultaneously. By exploiting picoliter-scale drops on demand, we form a low-density channel network near the source and drain junctions and a high-density network at the middle of the channel. The modulated density profile forms a large band gap near the source and drain junctions that efficiently blocks electron injection under the reverse bias and a narrow band gap at the high-density area that facilitates the hole transport under the on-state bias. As a result, the density-modulated SWCNT TFTs show both high carrier mobility (27.02 cm2 V-1 s-1) and a high on/off ratio (>106). We also demonstrate all-inkjet-printed flexible inverter circuits whose gain is doubled by the density-modulated SWCNT TFTs, highlighting the feasibility of our approach for realizing high-performance flexible and conformable electronics.

Standalone real-time health monitoring patch based on a stretchable organic optoelectronic system.

Skin-like health care patches (SHPs) are next-generation health care gadgets that will enable seamless monitoring of biological signals in daily life. Skin-conformable sensors and a stretchable display are critical for the development of standalone SHPs that provide real-time information while alleviating privacy concerns related to wireless data transmission. However, the production of stretchable wearable displays with sufficient pixels to display this information remains challenging. Here, we report a standalone organic SHP that provides real-time heart rate information. The 15-µm-thick SHP comprises a stretchable organic light-emitting diode display and stretchable organic photoplethysmography (PPG) heart rate sensor on all-elastomer substrate and operates stably under 30% strain using a combination of stress relief layers and deformable micro-cracked interconnects that reduce the mechanical stress on the active optoelectronic components. This approach provides a rational strategy for high-resolution stretchable displays, enabling the production of ideal platforms for next-generation wearable health care electronics.

Dense Assembly of Finely Patterned Semiconducting Single-Walled Carbon Nanotubes via a Selective Transfer Method of Nanotube-Attracting Layers.

Development of technology for assembled single-walled carbon nanotube (SWCNT) film with the fine resolution is an essential technique for penetrating practical electronic applications. A promising approach is the assembly method by adding a chemical-functionalizing substrate to enhance affinity between the SWCNTs and the substrate. However, the various introduced approaches for solution-based assembly have suffered from low SWCNT deposition selectivity or low SWCNT deposition density. Herein, we demonstrated a facile method for selectively assembling semiconducting SWCNT network on the substrate. The substrate was prepared via a transfer printing of a poly-l-lysine (PLL)-coated poly(dimethylsiloxane) (PDMS) stamp. The thermal-assisted transfer method enabled an ultrafine PLL pattern (≤4 µm) and a high transfer yield (96.5%) by only one-time stamping without a change of the SWCNT-attracting nature. So, semiconducting SWCNTs were deposited on the patterned regions selectively and precisely. The benefit of the patterned semiconducting SWCNTs was lowering leakage current and turn-on voltage in the transfer characteristics by suppressing attachment of unnecessary SWCNT network. They showed excellent electrical performance, a log10(Ion/Ioff) ratio of 4.76, and an average value of linear field-effect mobility of 7.56 cm2/(V s). This research provides a simple but high-quality assembling technique of semiconducting SWCNTs, thereby improving the feasibility of solution-processed SWCNT-TFTs.

Inhibitory effect of Streptococcus salivarius K12 and M18 on halitosis in vitro.

BACKGROUND: The aim of the study was to observe the antimicrobial activity of Porphyromonas gingivalis and Treponema denticola as well as the effect on reducing volatile sulfur compounds (VSCs). MATERIALS AND METHODS: After P. gingivalis and T. denticola were cultured with or without Streptococcus salivarius K12 and M18, VSCs were measured by Oral Chroma. In order to analyze the mechanism for malodor control, the antimicrobial activity of S. salivarius K12 and M18 against P. gingivalis and T. denticola was assessed. SPSS 21.0 was used for data analysis with the Kruskal-Wallis and Jonckheere-Terpstra tests. Mann-Whitney test was applied for post hoc analysis. RESULTS: P. gingivalis and T. denticola VSC levels were reduced by high concentrations of S. salivarius K12 and M18 during coculture. The concentrations were lower than those of single culture (p < .05). An antimicrobial effect was detected on P. gingivalis, and T. denticola by 50% S. salivarius K12 and M18. The spent culture medium and whole bacteria of S. salivarius K12 and M18 reduced the levels of VSCs below the amount in a single culture of P. gingivalis and T. denticola (p < .05). CONCLUSION: S. salivarius K12 and M18 decreased the levels of VSCs originating from P. gingivalis and T. denticola.

Efficacy of ß-caryophyllene for periodontal disease related factors.

OBJECTIVE: This study aimed to investigate the antimicrobial activity of ß-caryophyllene against periodontopathogens as well as its inhibitory effects on the expression of inflammatory cytokines and production of volatile sulfur compounds by lipopolysaccharide and periodontopathogenic enzymes, respectively. DESIGN: The antimicrobial activity of ß-caryophyllene againstPorphyromonas gingivalis, Tannerella forsythia, and Treponema denticola was investigated via a susceptibility assay using a microplate reader. THP-1 cells were treated with lipopolysaccharide in the presence or the absence of ß-caryophyllene, and the expression and production of inflammatory cytokines were then analyzed by a real-time reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay. After fluorescence-labelling lipopolysaccharide, the effect of ß-caryophyllene on the binding of lipopolysaccharide to the cell wall was investigated via flow cytometry. The spent culture media of P. gingivalis was shaken with or without ß-caryophyllene and gaseous volatile sulfur compounds (VSCs) were measured by a gas chromatograph. RESULTS: ß-caryophyllene showed strong the antimicrobial activity against periodontopathogens. It also reduced lipopolysaccharide-induced expression and production of cytokines, thereby inhibiting the binding of lipopolysaccharide-binding to toll-like receptors by interfering with the complex of lipopolysaccharide and CD14 or lipopolysaccharide-binding protein. ß-caryophyllene also inhibited the emission of gaseous VSCs produced byP. gingivalis. CONCLUSIONS: ß-caryophyllene may improve periodontal health via antimicrobial activity against periodontopathogens, reducing inflammation caused by lipopolysaccharide, and by neutralizing VSCs.

Inhibitory effects of ß-caryophyllene on Streptococcus mutans biofilm.

OBJECTIVE: The biofilm of Streptococcus mutans is associated with induction of dental caries. Also, they produce glucan as an extracellular polysaccharide through glucosyltransferases and help the formation of cariogenic biofilm. ß-caryophyllene has been used for therapeutic agent in traditional medicine and has antimicrobial activity. The purpose of this study was to investigate the effect of ß-caryophyllene on S. mutans biofilm and the expression of biofilm-related factor. DESIGN: The susceptibility assay of S. mutans for ß-caryophyllene was performed to investigate inhibitory concentration for S. mutans growth. To evaluated the effect of ß-caryophyllene on S. mutans biofilm, ß-caryophyllene was treated on S. mutans in the various concentrations before or after the biofilm formation. Live S. mutans in the biofilm was counted by inoculating on Mitis-salivarius agar plate, and S. mutans biofilm was analyzed by confocal laser scanning microscope after staining bacterial live/dead staining kit. Finally, the expression of glucosyltransferases of S. mutans was investigated by real-time RT-PCR after treating with ß-caryophyllene at the non-killing concentration of S. mutans. RESULTS: The growth of S. mutans was inhibited by ß-caryophyllene in above concentration of 0.078%, S. mutans biofilm was inhibited by ß-caryophyllene in above 0.32%. Also, 2.5% of ß-caryophyllene showed anti-biofilm activity for S. mutans biofilm. ß-caryophyllene reduced the expression of gtf genes at a non-killing concentration for S. mutans. On the basis on these results, ß-caryophyllene may have anti-biofilm activity and the inhibitory effect on biofilm related factor. CONCLUSIONS: ß-caryophyllene may inhibit cariogenic biofilm and may be a candidate agent for prevention of dental caries.

Bulk layered heterojunction as an efficient electrocatalyst for hydrogen evolution.

We describe the spontaneous formation of composite chalcogenide materials that consist of two-dimensional (2D) materials dispersed in bulk and their unusual charge transport properties for application in hydrogen evolution reactions (HERs). When MoS2 as a representative 2D material is deposited on transition metals (such as Cu) in a controlled manner, the sulfidation reactions also occur with the metal. This process results in remarkably unique structures, that is, bulk layered heterojunctions (BLHJs) of Cu-Mo-S that contain MoS2 flakes inside, which are uniformly dispersed in the Cu2S matrix. The resulting structures were expected to induce asymmetric charge transfer via layered frameworks and tested as electrocatalysts for HERs. Upon suitable thermal treatments, the BLHJ surfaces exhibited the efficient HER performance of approximately 10 mA/cm2 at a potential of -0.1 V versus a reversible hydrogen electrode. The Tafel slope was approximately 30 to 40 mV per decade. The present strategy was further generalized by demonstrating the formation of BLHJs on other transition metals, such as Ni. The resulting BLHJs of Ni-Mo-S also showed the remarkable HER performance and the stable operation over 10 days without using Pt counter electrodes by eliminating any possible issues on the Pt contamination.

CALCULATION OF GAMMA SPECTRA IN A PLASTIC SCINTILLATOR FOR ENERGY CALIBRATIONAND DOSE COMPUTATION.

Plastic scintillation detectors have practical advantages in the field of dosimetry. Energy calibration of measured gamma spectra is important for dose computation, but it is not simple in the plastic scintillators because of their different characteristics and a finite resolution. In this study, the gamma spectra in a polystyrene scintillator were calculated for the energy calibration and dose computation. Based on the relationship between the energy resolution and estimated energy broadening effect in the calculated spectra, the gamma spectra were simply calculated without many iterations. The calculated spectra were in agreement with the calculation by an existing method and measurements.

PLASTIC SCINTILLATOR FOR RADIATION DOSIMETRY.

Inorganic scintillators, composed of high-atomic-number materials such as the CsI(Tl) scintillator, are commonly used in commercially available a silicon diode and a scintillator embedded indirect-type electronic personal dosimeters because the light yield of the inorganic scintillator is higher than that of an organic scintillator. However, when it comes to tissue-equivalent dose measurements, a plastic scintillator such as polyvinyl toluene (PVT) is a more appropriate material than an inorganic scintillator because of the mass energy absorption coefficient. To verify the difference in the absorbed doses for each scintillator, absorbed doses from the energy spectrum and the calculated absorbed dose were compared. From the results, the absorbed dose of the plastic scintillator was almost the same as that of the tissue for the overall photon energy. However, in the case of CsI, it was similar to that of the tissue only for a photon energy from 500 to 4000 keV. Thus, the values and tendency of the mass energy absorption coefficient of the PVT are much more similar to those of human tissue than those of the CsI.

Spatial charge separation in asymmetric structure of Au nanoparticle on TiO2 nanotube by light-induced surface potential imaging.

Both enhancing the excitons' lifetime and ingeniously controlling the spatial charge transfer are the key to the realization of efficiently photocatalytic and artificially photosynthetic devices. Nanostructured metal/metal-oxide interfaces often exhibit improved energy conversion efficiency. Understanding the surface potential changes of nano-objects under light illumination is crucial in photoelectrochemical cells. Under ultraviolet (UV) illumination, here, we directly observed the charge separation phenomena at the Au-nanoparticle/TiO2-nanotube interfaces by using Kelvin probe force microscopy. The surface potential maps of TiO2 nanotubes with and without Au nanoparticles were compared on the effect of different substrates. We observed that in a steady state, approximately 0.3 electron per Au particle of about 4 nm in diameter is effectively charged and consequently screens the surface potential of the underlying TiO2 nanotubes. Our observations should help design improved photoelectrochemical devices for energy conversion applications.

Rapid, conformal gas-phase formation of silica (SiO2) nanotubes from water condensates.

An innovative atomic layer deposition (ALD) concept, with which nanostructures of water condensates with high aspect ratio at equilibrium in cylindrical nanopores can be transformed uniformly into silica (SiO2) at near room temperature and ambient pressure, has been demonstrated for the first time. As a challenging model system, we first prove the conversion of cylindrical water condensates in porous alumina membranes to silica nanotubes (NTs) by introducing SiCl4 as a metal reactant without involving any catalytic reaction. Surprisingly, the water NTs reproducibly transformed into silica NTs, where the wall thickness of the silica NTs deposited per cycle was found to be limited by the amount of condensed water, and it was on the orders of ten nanometers per cycle (i.e., over 50 times faster than that of conventional ALD). More remarkably, the reactions only took place for 10-20 minutes or less without vacuum-related equipment. The thickness of initially adsorbed water layers in cylindrical nanopores was indirectly estimated from the thickness of formed SiO2 layers. With systematic experimental designs, we tackle the classical Kelvin equation in the nanosized pores, and the role of van der Waals forces in the nanoscale wetting phenomena, which is a long-standing issue lacking experimental insight. Moreover, we show that the present strategy is likely generalized to other oxide systems such as TiO2. Our approach opens up a new avenue for ultra-simple preparation of porous oxides and allows for the room temperature formation of dielectric layers toward organic electronic and photovoltaic applications.

Lateral redistribution of trapped charges in nitride/oxide/Si (NOS) investigated by electrostatic force microscopy.

Charge decay and lateral spreading properties were characterized by modified electrostatic force microscopy (EFM) under a high vacuum at elevated temperatures. Variations in the charge profiles were modeled with the maximum charge density (ρ(m)) and the lateral spreading distance (Δ(s)), as extracted from the EFM potential line profiles. The scaling limitation of nitride trap memory is discussed based on the projected lateral spreading distances for holes and electrons, which were determined to be approximately 18 nm and 12 nm, respectively, at room temperature.

Sensitive, label-free DNA diagnostics based on near-field microwave imaging.

Biological assays often rely on "reporter labels" to enhance measurement sensitivity, for example, by incorporation of a fluorescent dye or a nanoparticle into a nucleic acid or a protein. Use of labels, however, complicates sample preparation, increases assay costs, and can cause experimental artifacts by interfering with assay thermodynamics or limiting label stability. We evaluate near-field microwave imaging (NFMI) as an alternative, label-free technique for molecular diagnostics. Using DNA monolayers as an experimental model, NFMI is demonstrated to achieve sensitivities comparable to conventional fluorescence bioassays. Moreover, NFMI is shown to be compatible with imaging at resolutions required by microarray applications, as demonstrated by monitoring DNA hybridization in an array format.