[en] A visible photochemistry of maleic to fumaric acid adsorbed on silver nanoparticle surfaces was investigated as probed by SERS using a simple flow method. Photoisomerization of maleic to fumaric acid was consecutively observed in the condition of various flow rates, which varied the exposure time of laser beam. The sequential SERS spectra of maleic acid indicated that the photochemical isomerization and desorption took place simultaneously on silver nanoparticle surfaces as a function of laser fluency and wavelength. For 530.9 nm laser line excitation, the rate constant coefficients were obtained with a = 5.9 sec.1 mW for isomerization and b = 13.9 sec^-1 mW for desorption, which k₁ = aIⁿ and k₂ = bI^m. Both reactions were one photon process (n = 1, m = 1) of a visible light and relatively fast process whose decay time was in the range of milli-second for 50 mW laser power. The rate of photochemical reaction increased on going toward the blue and photodesorption was a dominant process. A simple flow method used in this study was very useful to study a relatively fast photochemical reaction of molecules adsorbed on silver nanoparticle surfaces

[en] In this study we analyzed and improved an experiment measuring chemical reaction rates introduced in the high school science textbooks through an understanding of the phenomena observed in carrying out the experiment. For this purpose, the contents of textbooks related to the experiment were analyzed, and the problems observed in carrying out the experiment were addressed through experimental analysis. When the experiment was carried out by the method of aquatic transposition presented in textbooks, the observed volume change of H₂ gas was delayed and chemical reaction rate was increased in the early stage of reaction period. To resolve these problems, an improved method for measuring the reaction rates was suggested. In the improved experiment the reaction rate was measured to be constant on time, which was interpreted in terms of the concentration of H⁺ and the surface area of magnesium

[en] In this study, a localized surface plasmon resonance sensor using an optical fiber was fabricated and experimentally proven for the possibility of achieving a biosensor by detecting a combination of peptides using the reaction of transglutaminase. To enhance the performance of a fiber-optic localized surface plasmon resonance (FO LSPR) sensor, we propose to improve the surface condition of an etched optical fiber. A process condition that is able to control the diameter and surface density ratio of gold nanoparticles on the etched optical fiber was established and the sensor with optimized sensitivity was fabricated through optical analysis of varying diameters and surface density ratios of gold nanoparticles. The proposed FO LSPR sensor is expected to measure various biological reactions, and it can be applied to various biological applications

[en] We report the fabrication of a patterned polymer electrolyte for a two-dimensional (2D) semiconductor, few-layer tungsten diselenide (WSe_2) field-effect transistor (FET). We expose an electron-beam in a desirable region to form the patterned structure. The WSe_2 FET acts as a p-type semiconductor in both bare and polymer-covered devices. We observe a highly efficient gating effect in the polymer-patterned device with independent gate control. The patterned polymer gate operates successfully in a molybdenum disulfide (MoS_2) FET, indicating the potential for general applications to 2D semiconductors. The results of this study can contribute to large-scale integration and better flexibility in transition metal dichalcogenide (TMD)-based electronics.

[en] Highlights: • Dual-modal using fluorescence and SERS for high-throughput multiplex analysis. • 45 different F_QDR_SERS signals obtained from three fluorescent and 15 SERS signals. • A barcode-based machine learning identification algorithm. • A multiplex detection platform: nanoprobes and high-throughput analysis algorithm. Biological encoding, multiplex biomarker imaging, and immunoassays require a multiplex spectroscopic detection and analysis technique that uses surface-enhanced Raman scattering (SERS)-based dual-modal nanoprobes. In the present study, dual-modal fluorescence–SERS quantum dot (QD)-embedded silver bumpy nanoparticles are developed for high-throughput multiplex analysis. Forty-five different dual-modal (F_RGBR_SERS) nanoprobes are prepared from silica-coated silver bumpy nanoshells (AgNS@SiO₂) with 15 different types of Raman label compounds and 3 types of QDs (red, green, and blue). Each F_RR_SERS nanoprobe produces strong SERS and fluorescence signals for multiplex analysis. Based on this dual-modality, a barcode-based machine learning algorithm that transforms spectra into barcodes and identifies chemical information is created. As a proof-of-concept experiment, single- and triplex-label spectra are identified from a library comprising 15 types of Raman labels. The multiplex detection platform comprising the F_RR_SERS nanoprobes and the high-throughput analysis algorithm will be extremely useful for analyzing and encoding biological targets.

[en] Smart fabrics have attracted considerable attention due to their potential applications. The essential features of smart fabrics include wearability, weaveability, and stretchability, as well as their sensing/response capability, which is frequently based on electrical measurement. Thus, the electromechanical behavior of these fabrics is considered the most important material property. Here, we report the negative piezoresistance of single-walled carbon nanotube coated cotton yarn (SWNT-CY). The gauge factor (the ratio of the normalized change in piezoresistance to the change in strain) of SWNT-CY is measured to be − 24. It is noteworthy that the factor is negative and an order of magnitude higher than that for conventional metal strain gauges. The negative piezoresistance is due to mechanical contact between fabric fibers, which leads to better electrical paths of SWNT networks. The conduction behavior can be modeled as fluctuation-induced tunneling (FIT) through the contact barriers between conducting regions. The effective barrier strength of strained SWNT-CY is measured to be ∼ 30% lower than that of unstrained SWNT-CY. This characteristic may offer new design opportunities for wearable electronics and has significant implications for sensor applications

[en] N-type graphene fabricated by exposure to hydrogen gas has been previously studied. Based on this property of graphene, herein, we demonstrate local doping in single-layer graphene using selective adsorption of dissociative hydrogen at 350 K. A graphene field effect transistor was produced covered with PMMA on half of the graphene region. The charge neutrality point of the PMMA-window region shifted to a negative gate voltage (V_G) region prominently compared with that of the PMMA-covered region. Consequently, a single graphene p-n junction was obtained by measuring the V_G-dependent resistance of the whole graphene region. This method presents opportunities for developing and controlling the electronic structure of graphene and device applications

[en] Surface-enhanced Raman scattering (SERS) has a great potential as a sensitive probe for analytical detection, but the low level of reproducibility remains a challenge for quantitative detection. To enhance the reproducibility, an internal standard that is incorporated between the core and shell structure of metal nanoparticles (NPs) can be employed. However, the unstable sol form of “core-shell” substrates has been unsatisfactory, causing rapid agglomeration. Herein, we prepared a SERS-active core-Raman labeling chemical (RLC)-shell material based on Au-Ag NPs assembled on silica NPs (SiO₂@Au@RLC@Ag NPs) as internal-standard-containing NPs. When 4-mercaptobenzoic acid (4-MBA) was used as a model RLC with a silica template, the Raman intensity of SiO₂@Au@4-MBA@Ag was ∼8-fold higher than that without a silica template (Au@4-MBA@Ag NPs). Concentrations of 4-MBA in the range of 1 × 10⁻⁶ to 1 × 10⁻² M incorporated between the SiO₂@Au core and the Ag shell did not significantly affect the Ag shell coating. Nevertheless, the Raman intensity increased linearly and was proportional to the logarithm of the 4-MBA concentration. When SiO₂@Au@4-MBA@Ag was utilized as internal-standard-containing NPs, the dynamic linear range of thiram detection was 5–50 μM with a limit of detection of 1.2 μM. These results show that our material can be used for the broad dynamic detection of (bio)-chemical traces with high sensitivity.

[en] We report the electron doping of single-layer graphene (SLG) grown by chemical vapor deposition (CVD) by means of dissociative hydrogen adsorption. The transfer characteristic showed n-type doping behavior similar to that of mechanically exfoliated graphene. Furthermore, we studied the thermoelectric power (TEP) of CVD-grown SLG before and after exposure to high-pressure H₂ molecules. From the TEP results, which indicate the intrinsic electrical properties, we observed that the CVD-grown SLG is n-type doped without degradation of the quality after hydrogen adsorption. Finally, the electron doping was also verified by Raman spectroscopy

[en] Surface-enhanced Raman scattering techniques have been widely used for bioanalysis due to its high sensitivity and multiplex capacity. However, the point-scanning method using a micro-Raman system, which is the most common method in the literature, has a disadvantage of extremely long measurement time for on-chip immunoassay adopting a large chip area of approximately 1-mm scale and confocal beam point of ca. 1-μm size. Alternative methods such as sampled spot scan with high confocality and large-area scan method with enlarged field of view and low confocality have been utilized in order to minimize the measurement time practically. In this study, we analyzed the two methods in respect of signal-to-noise ratio and sampling-led signal fluctuations to obtain insights into a fast and reliable readout strategy. On this basis, we proposed a methodology for fast and reliable quantitative measurement of the whole chip area. The proposed method adopted a raster scan covering a full area of 100 μm × 100 μm region as a proof-of-concept experiment while accumulating signals in the CCD detector for single spectrum per frame. One single scan with 10 s over 100 μm × 100 μm area yielded much higher sensitivity compared to sampled spot scanning measurements and no signal fluctuations attributed to sampled spot scan. This readout method is able to serve as one of key technologies that will bring quantitative multiplexed detection and analysis into practice