A Collection of the Research  
     2015-present (see below)
    2015-present  2014  2013  2012  2011  2010-2007

Research Topics (in Japanese)

    ニュースレター/News Letter: No.5 (2015)  No.4 (2015)  No.1-3 (2007-2009)

Photonics Innovation (in Japanese)

A Collection of the Research  2015-present 

The crystal growth mode is switched from 2D nucleation growth (left) to spiral growth (right) by femtosecond laser ablation. The spiral growth mode is energetically advantageous for growth at low supersaturation compared with the 2D nucleation growth mode, and thus enhances the crystal growth rate.

We find that femtosecond laser ablation enables us spatiotemporally switch the crystal growth mode, which allows larger protein crystals to be obtained. In addition, the spatiotemporal features of our technique will be useful for controlling crystal shape, which is important for reducing anisotropic X-ray diffraction. We previously reported that femtosecond laser ablation of supersaturated solutions can trigger the nucleation of various compounds, including drug targeted proteins. Thus, the implementation of controlled nucleation and crystal growth by femtosecond laser ablation opens up the possibility of laser ablation for bottom-up fabrication and also enhance structure-based protein studies that have heretofore been considered extremely difficult.

Promotion of protein crystal growth by actively switching crystal growth mode via femtosecond laser ablation

Yusuke Tominaga, Mihoko Maruyama, Masashi Yoshimura, Haruhiko Koizumi, Masaru Tachibana, Shigeru Sugiyama, Hiroaki Adachi, Katsuo Tsukamoto, Hiroyoshi Matsumura, Kazufumi Takano, Satoshi Murakami, Tsuyoshi Inoue, Hiroshi Y. Yoshikawa and Yusuke Mori

Nature Photonics(2016) doi:10.1038/nphoton.2016.202

Maps of electric FE factor at resonance conditions for the experimental structures that support (a) SPP mode, (b) coupled S-SPP and SPP modes; (c) experimental; and (d) theoretical optimized structure that support coupled SPP and WG modes.

We discussed in this paper important implications in the field of nanophotonics, including the possibility of tuning the optical properties in plasmonic devices based on the control of dispersion relations in MIM structures, and the potential of ultra-sensing and giantly enhanced spectroscopy using PIT and Fano resonances in SPP-PWG hybrid structures. We hope that researchers of the nanophotonics and plasmonics communities will adopt the study discussed in this paper for their future work.

Plasmonic coupled modes in metal-dielectric multilayer structures: Fano resonance and giant field enhancement


Vol. 24, No. 18 | 5 Sep 2016 | OPTICS EXPRESS 20080

Fluorescence labeling of PYP tag using AT-DNB2.

We demonstrated that fluorogenic probes of different colors for labeling a protein tag are powerful tools for visualizing the dynamic movement of GLUT4. Imaging analyses using the fluorogenic PYP-tag probes verified the importance of N-glycosylation in GLUT4 retention on the cell membrane. Cell membrane retention is critical for glucose transport in insulin signaling. Lowering of the retention time leads to the reduction of glucose transport, resulting in increased blood sugar levels, which could cause type II diabetes. Therefore, this finding will be valuable for research on type II diabetes and its treatment. Moreover, the use of this system is not limited to GLUT4; it will also be useful for studying various membrane proteins whose cellular localization changes dynamically in response to external signals.

Fluorogenic probes reveal a role of GLUT 4 N-glycosylation in intracellular trafficking

Shinya Hirayama, Yuichiro Hori, Zsolt Benedek, Tadashi Suzuki & Kazuya Kikuchi

NATURE CHEMICAL BIOLOGY published online: 22 August 2016

Enhanced Raman spectroscopy of Rhodamine 6G (R6G) molecules using silver nano-trees. (a) SEM image of the grown silver nano-trees. The scale bar is 500 μm. (b) Fluorescence microscope image of (a) covered with R6G (10 μM) aqueous solution. The fluorescence from R6G is quenched by the silver nano-trees, resulting in a dark star pattern. (c) SERS spectrum of R6G on the silver nano-trees obtained in the red circle area in (a) and (b). Strong Raman peaks assigned to vibrational modes of R6G are clearly observed, which can be attributed to the large enhancement effects provided by the silver nano-trees. (d) Same as (c) but taken on a different area without the silver nano-trees denoted by the green circle area in (a) and (b). For both measurements, the exposure time was 1 sec, and the laser power was 1.0 and 0.13 mW, respectively.

We have developed a self-growing method of metallic metamaterials that exhibit fractal geometry with self-similarity. Plasmonic heating with UV light illumination triggers the growth at seeds and needle tips. Silver nano-trees are grown in silver ion solution due to the diffusion of ions and reduction of silver crystals. No use of surfactant helps to form trees with branches and sub-branches. We described the protocol of the self-growth fabrication and analyzed the fractal dimensions of the structures. An application of the developed structures was shown through experiments of surface enhanced Raman sensing of molecules with large enhancement due to its fractal nature.

Plasmonic growth of patterned metamaterials with fractal geometry

Nobuyuki Takeyasu, Natsuo Taguchi, Naoki Nishimura, Bo Han Cheng, and Satoshi Kawata

APL PHOTONICS 1, 050801 (2016)

Optical properties of an individual aluminum nanodisk placed on a metallic back reflector. (a) Schematic of the top view (left) and the cross-section (right) of an aluminum nanodisk placed on an aluminum oxide-coated aluminum film. (b) Simulated absorption map of individual aluminum nanodisks (not periodic) with different nanodisk diameters. (c) Electric field distributions near the nanodisk (d = 160 nm) illuminated at wavelengths of 370 nm (left) and 815 nm (right). The electric field is normalized to the incident field |Eo|.
We have demonstrated an intuitive and general design approach based on individual gap-plasmonic antennas to create full-color printed images and letters with a resolution of the diffraction limit of light. Individual antenna properties that exhibit strong light absorption at two distinct frequencies could be encoded into single subwavelength-pixels, enabling saturated color generation in reflection at the diffraction limit. A black color could also be created by mixing differently sized antennas into a single pixel to achieve strong absorption over the whole visible light range. The suitability of these color pixels for subwavelength printing applications was demonstrated by showing microscopic letters in color, the incident polarization and angle insensitivity, and color durability. We believe that the proposed design strategy provides a general platform for the practical utilization of subwavelength-scale plasmonic colors.

Full-Color Subwavelength Printing with Gap-Plasmonic Optical Antennas

Masashi Miyata, Hideaki Hatada, and Junichi Takahara 

Nano Lett., 2016, 16, 3166−3172

(a) Schematic of the tip structure for plasmon nanofocusing (a dielectric pyramidal structure and a metallic thin layer on its surface). By illuminating the grating with a laser, plasmon nanofocusing is induced to generate near-field light at the apex. (b) An intensity map of FDTD simulation of electric field in the vicinity of the tip apex during plasmon nanofocusing (c) SEM image of a fabricated tip. (inset: an enlarged image of the tip, where a grating structure was fabricated on the thin and smooth silver layer)

Near-field scanning optical microscopy (NSOM) combined with plasmon nanofocusing is a powerful nano-analytical tool due to its attractive feature of efficient background suppression as well as light energy compression to the nanoscale. In plasmon nanofocusing-based NSOM, the metallic tip plays an important role in inducing plasmon nanofocusing. Here, the authors proposed an efficient tip design and fabrication which enable one to actively control plasmonic properties for efficient plasmon nanofocusing. Almost 100% reproducibility in plasmon nanofocusing was achieved in the experiments. This new approach of tip fabrication makes plasmon nanofocusing-based NSOM practical and reliable, and opens doors for many scientists working in related fields.

Highly efficient plasmonic tip design for plasmon nanofocusing in near-field optical microscopy

Takayuki Umakoshi, Yuika Saito & Prabhat Verma

Nanoscale, 8, 5634 (2016) | DOI: 10.1039/c5nr08548a

Detection of extremely small amounts of (a) polycarbamate and (b) benomyl pesticides on orange through PERRS (ex λ = 532 & 785 nm) Spectra (i) from clean oranges, spectra (ii) from pure pesticides. Red dotted and cyan dashed vertical lines indicate prominent Raman modes from pesticides and oranges. Spectra (iii) resonant Raman scattering from oranges after a small amount of pesticide was dropped onto it and then washed off with water. These spectra show only citrus peaks; no pesticide could be detected. Spectra (iv) were taken after dropping small amounts of (a) GNSs and (b) GNRs. Raman modes from pesticides were strongly enhanced, and modes associated to both citrus and pesticides could be observed.

A small residual of pesticide on food can be harmful. It is great important to develop a robust technique to detect tiny amounts of pesticides. Here, particle-enhanced resonant Raman spectroscopy was newly proposed to detect extremely low concentrations of pesticides, where gold nanoparticles of desired plasmonic resonance are synthesized to match the resonance in Raman scattering. The detection of extremely low amounts of pesticides on oranges was successfully demonstrated.

High-sensitivity pesticide detection using particle-enhanced resonant Raman scattering

Bikas Ranjan, Yuika Saito & Prabhat Verma

Applied Physics Express 9, 032401 (2016) | DOI: 10.7567/APEX.9.032401

(a) TEM micrograph of Pt NCs@PEI
     (scale bar=10 nm)

(b) histograms of their size-distribution.


(a) differential interference contrast imaging & 
(b) laser confocal fluorescence microscopy of living HeLa cells labelled with Pt NCs@PEI
-(anti-CXCR4-Ab) conjugates (scale bar=20 µm)
The formation of yellow fluorescent polyethylenimine-protected platinum nano-clusters (Pt NCs@PEI) synthesized by a facile one-pot reduction method was investigated. Pt NCs were produced in the cavities formed by coiled PEI ligands and were mostly stabilized with the amino groups. Pt NCs@PEI with an average diameter of 1.4 ± 0.4 nm demonstrated excellent photo-stability against high salt concentration and long-term light exposure. By conjugating Pt NCs@PEI with the chemokine receptor anti-CXCR4 antibody, Pt NCs@PEI-(anti-CXCR4-Ab) conjugates were successfully applied to bio-imaging of the membrane of live HeLa cells that had their nuclei stained with DAPI. Moreover, Pt NCs@PEI showed lower cell cytotoxicity than Qdots@COOH, indicating that they have better cell viability and great potential for bio-applications.

Formation of fluorescent platinum nanoclusters using hyper-branched polyethylenimine and their conjugation to antibodies for bio-imaging

Xin Huang, Hidekazu Ishitobi & Yasushi Inouye

RSC Advances 6, 9709-9716 (2016) | DOI: 10.1039/c5ra24522b

Light from the laser is split by a phase grating to produce interference fringes in the line illumination at the sample.

Raman images of a mouse brain slice. (a,b) The intensity distribution of Raman peaks at 1,682 cm-1 (red) and 2,848 cm-1  (green) imaged by the LI (a) and SLI (b) microscopes (Scale bar, 5 um). Raman peaks at 1,682 cm-1  and 2,848 cm-1 can be assigned to amide-I and CH2 stretching vibrational modes, respectively, predominantly observed in protein beta sheets and lipids.
Structured-line illumination (SLI) Raman microscopy that we have developed shows a well-balanced performance in spatial and spectral resolution with the capability of optical sectioning and powerful spectral analysis. The spatial resolution provided by SLI can reach the theoretical limit of confocal microscopy in many practical applications. Considering the SNR in the detection of Raman scattering, SLI Raman microscopy can realize a remarkable improvement in spatial resolution over that of current Raman imaging techniques, and which can further expand the application of Raman microscopy in various research fields such as material sciences, life sciences and pharmaceuticals. For example, our technique can lead to the detailed analysis of graphene, which is important in understanding fundamental questions on graphene sheet growth mechanism and characterization of graphene devices. In cell biology, as fluorescence SIM has contributed to visualize the detailed structure of cellular components, it might also be possible to spectrally distinguish these components even without staining by using the SLI Raman technique. In pharmaceuticals, an emerging demand that can benefit from the high spatial resolution of SLI Raman microscopy is the precise determination of the distribution of the different chemical components in a drug.

Structured line illumination Raman microscopy

Kozue Watanabe, Almar F. Palonpon, Nicholas I. Smith, Liang-da Chiu, Atsushi Kasai, Hitoshi Hashimoto, Satoshi Kawata & Katsumasa Fujita

NATURE COMMUNICATIONS | 6:10095 | DOI: 10.1038/ncomms10095

Published 2 Dec 2015

(a) Raman spectra of graphene sheets scattered with Ag tip having rough (left panel) and smooth (right panel) surface. The spectra are vertically shifted for clarity. The insets show scanning electron micrograph (SEM) of the tip used. The scale bar is 100 nm. (b) SEM of disconnected Ag grains coated on SiO2 cone probe. (c) Raman spectra of a graphene sheet measured with the disconnected multiple grain tip. The spectra are vertically shifted for clarity.

(a) Raman spectra of carbon nanotube (CNT) bundles scattered with the disconnected multiple grain tip. The spectra are vertically shifted for clarity. The SEM image of the probe having disconnected Ag grains is shown in the inset. (b)–(d) TERS images of CNTs measured with the disconnected multiple grain tip are shown at G-band, radial breathing mode (RBM), and 2D-band, respectively. The line profile of Raman intensity is shown in (b) along the dashed line. (e) Topographic image of CNT simultaneously taken during scan.
Tip-enhanced Raman spectroscopy (TERS) has recently become one of the most important tools for analyzing advanced nano-devices and nano-materials, because it allows strong enhancement of weak Raman signal from the nanometric volume of a sample. However, consistent enhancement in TERS is still an issue and scientists have been struggling to fabricate good tips for reliable, strong and reproducible enhancement. There is a strong need to study the morphology and the arrangement of metal nanostructures near the tip apex for efficient plasmonic enhancement in TERS. Here, we present a study on the metal grains attached to the tip surface for producing higher and much consistent enhancement in TERS. Our study shows that the plasmonic enhancement strongly depends on the number of grains and on their separations. We found through simulations that multiple grains arranged closely but discretely on a dielectric probe act as an efficient plasmonic antenna and that enhancement in TERS is maximum for an optimized number of grains. The number of grains and the nano-gap between them are crucial for reproducible enhancement. This promising result, which we also demonstrate and prove by experiments, will bring TERS to a new level, where it can be utilized with more confidence of large reproducible enhancement for those nano-sized samples that have extremely weak Raman scattering.

Optical antennas with multiple plasmonic nanoparticles for tip-enhanced Raman microscopy

Atsushi Taguchi, Jun Yu, Prabhat Verma and Satoshi Kawata

Nanoscale, 2015, 7, 17424–17433

Electroluminescence of europium-doped GaN LED with different applied voltages (inset: Photo-luminescence from Eu-doped GaN)
Historically, to realize red LED, band gap engineering employing crystal growth techniques, devices with built-in In-rich thin layer and nano-columns have been studied extensively. Alternative approach, Europium-doped GaN developed by Yasufumi Fuijiwara at Osaka University has excellent luminescence properties in the red spectral region, resulting from the specific optical properties of rare-earth elements. This includes a sharp, intense, temperature-independent emission peak associated with intra-4f shell transitions. The Osaka University team has used MOCVD to grow europium-doped GaN layers with high crystalline quality, and demonstrated low-voltage, current-injected red emission from p-type GaN/GaN:Eu/n-type GaN LEDs: emitting light at a forward voltage of just 3 V at 621 nm with output power increasing to 93 μW at 20 mA, an external quantum efficiency of 0.23 %. 
Doping of GaN with europium enables a red LED to join forces with blue and green cousins and form a monolithic, full-colour chip

Europium propels the GaN LED into the red

Y. Fujiwara (Osaka Univerisity), W. Jadwisienczak, and F. Rahman (Ohio University)

Compound Semiconductors 21 (2015) review pp. 50-53

Illustration of ABEI-AuNP-GONR modified SPE.

llustration of the proposed ECL mechanism of ABEI-AuNP-GONR/SPE.
The mechanism of electrochemiluminescence (ECL) of an N-(aminobutyl)-N-(ethylisoluminol)-functionalized gold nanoparticle (ABEI-AuNP) hybrid with graphene oxide nanoribbons (GONRs) as a functional supporting matrix on a modified screen-printed electrode (SPE) was studied under alkaline conditions. In our catalytic system, ABEI-AuNPs supported by GONRs were profoundly superior to the unsupported ABEI-AuNP/SPE, and exhibited greatly enhanced ECL intensity (ca., 30.0%). This difference is attributed not only to an 80.2% increase in the total surface area of the ABEI-AuNP-GONR/SPE, but also to enhancements of the ABEI-AuNP catalytic activity resulting from metal-oxygen bonding between the functional groups on the GONRs and the Au active sites. This improved catalytic activity of ABEI-AuNP facilitates both oxidative radical generation and fast reaction kinetics of the ABEI oxidation process. Further work to utilize ABEI-AuNP-GONR/SPE in an enzyme-based ECL sensor is being undertaken in the authors’ laboratory, which will pave the way for future developments of rapid and portable point-of-care device. 

Enhanced Electrochemiluminescence of N-(aminobutyl)-N-(ethylisoluminol) Functionalized Gold Nanoparticles by Graphene Oxide Nanoribbons

Nur Syakimah Ismail, Quynh Hoa Le, Quamrul Hasan, Hiroyuki Yoshikawa, Masato Saito, Eiichi Tamiya

Electrochimica Acta 180 (2015) 409–418

Schematic illustration of the enzyme-responsive fluorescence enhancement

Time-dependent fluorescence spectral changes (λex = 680 nm) of NGal-NIR-AuNPs/CHO-NIR-AuNPs (1.0 nM) in the presence of β-gal (1.0 μM)
We developed a novel enzyme-triggered NIR fluorescence enhancement nanosystem, which was obtained by the deliberate design and construction of functionalized AuNPs. The NIR fluorescence on the AuNPs was enhanced by a factor of 7.8 by β-gal. The increase induced by β-gal in electromagnetic resonance coupling between the AuNPs and the fluorophores gave rise to an increase in kr and light scattering intensity, both of which substantially contribute to the fluorescence enhancement. This novel strategy for the design of NIR fluorescent sensors will be widely applicable for the development of various enzyme-detection systems by the introduction of specific substrates on AuNPs. The new NIR fluorescence enhancement principle described here will be useful in the in-demand imaging techniques, such as in vivo enzyme detection and early diagnostic imaging. Although some challenges remain for the in vivo applications, they will be overcome by the integration with some advanced technologies such as stimuli-responsive polymers or active targeting technologies.

An enzyme-responsive metal-enhanced near-infrared fluorescence sensor based on functionalized gold nanoparticles

Zhanghua Zeng, Shin Mizukami, Katsumasa Fujita and Kazuya Kikuchi

Chem. Sci., 2015, 6, 4934–4939

Multimodalmeasurement of polystyrene beads and calibration of the two imaging modes. The beads can be seen (a) in the Raman channel at   1003 cm−1, with (b) their corresponding spectrum. They can also be identified as defocused diffraction patterns in (c) the hologram, or as black dots in the corresponding (d) reconstructed amplitude image. (e) The images are then automatically registered, and shown merged with the Raman channel in red and the inverted DHM amplitude in green. Slight remaining discrepancies in position result from distortions between the two modes. Scale bars are 10 μm.
Schematic and implementation of the DHM setup
We present a technical overview of a multimodal system combining Raman microspectroscopy and quantitative phase microscopy (QPM), which allows two independent and simultaneous measurements of both the local molecular content and dynamic sample morphology. We present in detail the setup implementation and measurement procedure, and show how different features of QPM can be used to ensure optimal Raman measurement conditions and matched fields of view, through off-line calibration procedures such as digital propagation of the measured complex field and analysis of the system’s optical aberrations which can then be employed for numerical compensation and calibration. We present measurements on live cells, where images based both on the quantitative phase signal and on the Raman molecular contrast can simultaneously be retrieved and compared. The dynamic measurements obtained from QPM also enable the monitoring of the cell morphology during the laser scanning of the Raman measurement, making it possible to identify the movements which may occur during the measurement.

Implementation of simultaneous quantitative phase with Raman imaging

Nicolas Pavillon and Nicholas I Smith

EPJ Techniques and Instrumentation (2015) 2:5
DOI 10.1140/epjti/s40485-015-0015-9

Fluorescence images of HeLa cells stained with (a) nitro-bisBODIPY and (b) BODIPY, measured with a laser scanning confocal microscope. The scales for signal values are the same in both images.
For super-resolution microscopy, the authors developed a new strategy to realize a probe with a nonlinear fluorescence response, a stepwise two-photon absorption scheme, by using photoinduced charge separation; the first photon for the generation of the charge-separated state and the second photon for fluorescence excitation. Transient absorption spectra studies and simulation indicate that fluorescence is emitted through the photophysical pathways they proposed. Fluorescence imaging of biological cells showed marked improvements in image contrast and resolution, demonstrating the usefulness of the fluorescent probe in laser scanning confocal microscopy.

Nonlinear fluorescence imaging by photoinduced charge separation

Kentaro Mochizuki, Lanting Shi, Shin Mizukami, Masahito Yamanaka, Mamoru Tanabe, Wei-Tao Gong, Almar F Palonpon, Shogo Kawano, Satoshi Kawata, Kazuya Kikuchi, and Katsumasa Fujita

Japanese Journal of Applied Physics 54, 042403 (2015)

A) Schematic illustration of the Pd/MoO3−x hybrid upon oxidation by O2 in air and reduction by NaBH4 in solution. B) The evolution of the optical response of Pd/MoO3−x hybrid exposed to air for different time periods. C) The optical absorption for the original Pd/MoO3−x hybrid, oxidized in air for 48 h, and the recovered product by NaBH4 reduction.
A facile solution reduction process was developed to prepare a semiconductor-based plasmonic Pd/MoO3−x hybrid, which was composed of Pd NPs anchored on MoO3−x plates and displayed intense LSPR in the visible-light region. As a generalized strategy, the synthetic protocol can also be applicable to other metal-NPs-decorated MoO3−x hybrids, such as Au and Pt. The Pd/MoO3−x hybrid underwent reversible tunability in their plasmonic resonance upon oxidation by O2 in air and reduction by NaBH4 in solution, and smaller Pd NPs were able to prolong the retention time of the plasmonic resonance of the hybrid. Under visible-light irradiation, the Pd/MoO3−x hybrid showed significant plasmon-enhanced catalysis for H2 production from NH3BH3 hydrolysis as well as Suzuki–Miyaura coupling reactions compared to dark conditions. This work illustrates the deficient chemistry induced plasmonic hybrid and their plasmon-enhanced catalysis, which provides tunable plasmonics in a wide range and will find more promising applications in solar-energy harvesting and conversion.

A Plasmonic Molybdenum Oxide Hybrid with Reversible Tunability for Visible-Light-Enhanced Catalytic Reactions

Hefeng Cheng, Xufang Qian, Yasutaka Kuwahara, Kohsuke Mori, and Hiromi Yamashita

Adv. Mater. 2015, 27, 4616–4621

Dark-field scattering images of a suspended gold NW illuminated by TM (the right middle) and TE (bottom) polarized light. The NW shows various scattering colors that range from red to green along the wire- length-axis under TM illumination, whereas the NW shows only a green color under TE illumination.
We present an experimental demonstration of nanoscale gap plasmon resonators that consist of an individual suspended plasmonic nanowire (NW) over a metallic substrate. Our study demonstrates that the NW supports strong gap plasmon resonances of  various gap sizes including single-nanometer-scale gaps. The obtained resonance features agree well with intuitive resonance models for near- and far-field regimes. We also illustrate that our suspended NW geometry is capable of constructing plasmonic coupled systems dominated by quasi-electrostatics.

Gap Plasmon Resonance in a Suspended Plasmonic Nanowire Coupled to a Metallic Substrate

Masashi Miyata, Aaron Holsteen‡, Yusuke Nagasaki, Mark L. Brongersma, and Junichi Takahara

Nano Lett., 2015, 15 (8), pp 5609–5616

Raman images of a pure diyne-SM monolayer (top: uniform intensity distribution) and a 1:1:1 diyne-SM/DOPC/chol ternary monolayer (bottom: diyne-SM was enriched in the central area  of the domain compared with the peripheral area) reconstructed using the diyne peak intensity at 2,263 cm−1. (Scale bar:10 μm.)
We synthesized an analog of sphingomyelin(SM) tagged with a small Raman active diyne moiety, which provides high chemical selectivity without affecting the membrane properties. Raman microscopy successfully visualized, at single lipid-layer sensitivity, a heterogeneous spatial distribution of this probe within raft-like ordered domains, which was different from the generally accepted raft model. This approach provides both chemical selectivity and quantitative imaging capability and is useful for functional studies of lipid rafts.

Sphingomyelin distribution in lipid rafts of artificial monolayer membranes visualized by Raman microscopy

Jun Ando, Masanao Kinoshita, Jin Cui, Hiroyuki Yamakoshi, Kosuke Dodo, Katsumasa Fujita, Michio Murata, and Mikiko Sodeoka

4558–4563| PNAS | April 14, 2015 | vol. 112

Streamline plots of the orientational patterns created by using the spiral bow-tie-shaped slit 
on a glass plate, for topological charges or defect strengths of 1, 2, and 3 (top from the left to the right). The nematic liquid crystal aligns along the streamlines as shown by corresponding POM images of liquid crystal cells (bottom).

(Left) Three-dimensional profile of the disclination network formed between spirally patterned glass substrates with (s, c)=(1, 0), calculated from a Landau–de Gennes theory. The cell gap has been extended twofold for clarity. (Right) POM image of the disclination network decorated with colloidal particles of 3 μm in diameter. The white dashed line indicates the direction along which the cross-sectional profile was measured. Scale bar, 20 μm.
Topological defects in liquid crystals not only affect the optical and rheological properties of the host, but can also act as scaffolds in which to trap nano or micro-sized colloidal objects. The creation of complex defect shapes, however, often involves confining the liquid crystals in curved geometries or adds complex-shaped colloidal objects, which are unsuitable for device applications. Using topologically patterned substrates, here we demonstrate the controlled generation of three-dimensional defect lines with non-trivial shapes and even chirality, in a flat slab of nematic liquid crystal. By using the defect lines as templates and the electric response of the liquid crystals, colloidal superstructures are constructed, which can be
reversibly reconfigured at a voltage as low as 1.3V. Three-dimensional engineering of the defect shapes in liquid crystals is potentially useful in the fabrication of self-healing composites and in stabilizing artificial frustrated phases.

Three-dimensional positioning and control of colloidal objects utilizing engineered liquid crystalline defect networks

H. Yoshida, K. Asakura, J. Fukuda, and M. Ozaki
Received 23 December 2014 Accepted 14 April 2015 Published 21 May 2015

NATURE COMMUNICATIONS | DOI: 10.1038/ncomms8180

SEM (A), TEM (B) and EDX (C) (red spots represent the existence of AgNPs) images of AgNPs–EVOH monolith. SERS spectrum (blue) of R6G collected from the monolith and Raman spectrum (red) of the monolith (without R6G) (D).
A facile method to fabricate a mesoporous poly(ethylene-co-vinyl alcohol) (EVOH) monolith captured with silver nanoparticles (AgNPs) was developed. The formation of AgNPs and the monolith was in a one-pot process. The obtained monolith demonstrated ultrasensitive surface-enhanced Raman spectroscopy (SERS) responses.

Mesoporous poly(ethylene-co-vinyl alcohol) monolith captured with silver nanoparticles as a SERS substrate: facile fabrication and ultra-high Sensitivity

Guowei Wang, Hiroyuki Yoshikawa, Eiichi Tamiya and Hiroshi Uyama

RSC Adv., 2015, 5, 25777