Schematic of the focus locking system consisting of an objective lens, a sample stage and capacitive sensor. The capacitive sensor senses the gap between the sensor electrode and the counter electrode (sample stage). An AFM head employing a cantilever is used for tip-enhanced spectroscopy, in which the tip has to be kept within the tight focus for a long time. PC: personal computer, DAAD: digital–analog and analog–digital converter. Confocal micro-Raman images of semiconductive SWNTs (a) with and (b) without a feedback. The cross-sectional profiles at the dashed lines are plotted in (c). The excitation laser wavelength and the power at the tight focus are 532 nm and 500 uW, respectively. Each pixel consists of 50 nm in size and 10 ms in exposure time.
diffraction limit is also plotted. The tip is adjusted to the peak position of the longitudinal field for the best tip-enhancement effect.
We have successfully stabilized the tight focus onto the sample surface of an optical microscope within +/-1.0 nm for a virtually unlimited time duration. The time-dependent thermal drift of the tight focus and the mechanical tilt of the sample surface were simultaneously sensed by a non-optical means based on a capacitive sensor and were compensated for in real-time. This non-optical scheme is promising for the suppression of background light sources for optical microscopy. The focus stabilization is crucial for microscopic measurement at an interface, particularly when scanning a large surface area, because there is always a certain amount of mechanical tilt of the sample substrate, which degrades the contrast of the image. When imaging nanoscopic materials such as carbon nanotubes or silicon nanowires, more stringent nanometric stabilization of the focus position relative to such samples is required, otherwise it is often difficult to interpret the results from the observations. Moreover, the smaller the sample volume is, the smaller the signal becomes, resulting in a long exposure time at each position. In this sense, long-term stability of the tight focus is essential for both microscopic large area scanning and nanosized sample scanning (high-resolution/large-area imaging). In addition, the recently developed tip-enhanced microscopy requires long-term stability of the relative position of the tip, sample and focus position. We were able to successfully demonstrate a stability improvement for tip-enhanced microscopy in the same manner. The stabilization of the tight focus enables us to perform long-term and robust measurements without any degradation of optical signal, resulting in the capability of true nanometric optical imaging with good reproducibility and high precision. The technique presented is a simple add-on for any kind of optical microscope.
Nanometric locking of the tight focus for optical microscopy and tip-enhanced microscopy
N. Hayazawa, K. Furusawa and S. Kawata
Nanotechnology 23 (2012)465203
Microscope image of Gold SRRs fabricated on the silver-inserted substrate. Inset: enlarged image of the sample (left) and conceptual design of SRR array for thermal radiation control. Relative emittance of SRRs with the length Ly . 3:2, 2.6, and 2.1 um from (a) experimental results and (b) numerical results. The electric field is polarized parallel to the SRR gap (red) and perpendicular to it (blue). Insets show microscope images of a unit cell of SRR. For the polarization perpendicular to the SRR gap, peak positions blue-shift with decreasing height of SRR Ly.
We demonstrated experimentally for the first time in the world that the spectra of thermal radiation can be controlled by using a split-ring resonator (SRR) structure. Our calculations clearly showed that the experimental results can be attributed to SRR resonances. Furthermore, we achieved the artificial shift of the peak positions of the resonance with changing the length of the SRR structure. The functions of the metasurface discussed here will lead to thin-film emitters (from terahertz to visible frequency) in the future. The fabrication and measurement apparatuses in the Photonics Center are utilized for this experiment.
Spectral Control of Thermal Radiation by Metasurface with Split-Ring Resonator
Yosuke Ueba and Junichi Takahara
Appl. Phys. Express 5(2012) 122001
Three-dimensional, two-colour imaging of a vessel in rat liver. Images at wavenumbers of 2,850 and 2,950 cm-1 were successively taken while the z-position was scanned over 80 um in steps of 1 um. Total acquisition time is 5.3 s. Reconstructed three-dimensional image, Scale bars, 20 um.
We have demonstrated molecular spectral imaging based on high speed SRS (Raman scattering microscopy) spectral microscopy and modified ICA (independent component analysis). This system allows quick image acquisition at.30 frames/s by changing the wavenumber in a frame-by-frame manner. The modified ICA enables blind separation of constituents without a priori spectral data. The IC spectra give spectroscopic information, and the IC images can be used to produce multi colour images. This label-free and rapid observation method would be especially useful in medical imaging. We present various imaging modalities such as two-dimensional spectral imaging of rat liver, two-colour three-dimensional imaging of a vessel in rat liver, spectral imaging of several sections of intestinal villi in mouse, and in vivo spectral imaging of mouse ear skin.
High-speed molecular spectral imaging of tissue with stimulated Raman scattering
Yasuyuki Ozeki, Wataru Umemura, Yoichi Otsuka, Shuya Satoh, Hiroyuki Hashimoto, Kazuhiko Sumimura, Norihiko Nishizawa, Kiichi Fukui and Kazuyoshi Itoh
NATURE PHOTONICS VOL 6 |DECEMBER 2012
Note:In SRS microscopy, we use two-color laser pulses, one of which is intensity modulated in time. Then they are focused on a sample. When the optical frequency difference of the pulses matches the vibrational frequency of the sample molecules, the optical energy of the high-frequency pulse is transferred to the low-frequency pulse and to molecular vibrations through the SRS process. As a result, the intensity modulation is transferred to the other pulse, and this modulation transfer is measured by the lock-in detection technique. SRS has various advantages, such as accessibility to the vibrational spectrum without spectral distortion, quantitative image contrast, high sensitivity, and high imaging speed.
Influenza virus RNA was amplified by a continuous-flow polydimethylsiloxane microfluidic RT-PCR chip within 15–20 min. The amplified influenza virus RNA was observed with the naked eye, as the red color at the test line, using a lateral flow immunoassay within 1 min.
The amplified DNA from influenza virus RNA, using a fluorescein isothiocyanate (FITC) labelled primer and biotinylated primer, by the microfluidic continuous-flow reverse transcription PCR (RT-PCR) chip was detected by amplified DNA detection lateral flow immunoassay (ADLFIA). The sensitivity of ADLFIA is comparable to that of agarose gel electrophoresis. The detection by ADLIFA needs only the naked eye.
ADLFIA will be appended to a conjugate pad containing a dried excess volume of biotin antibody-labelled gold nanoparticles for a one-step assay. The conjugate pad appending ADLFIA can integrate easily into the solution exuding from the outlet of the chip. The integration enables the easy detection by ADLFIA without a mixing step. We are continuing our effort towards a battery powered portable PCR chip, and a battery powered portable PCR chip with ADLFIA has the potential to give the portable system a diagnostic test.
Schematic representation of the detection of the influenza virus using the continuous-flow RT-PCR chip and ADLFIA. Influenza virus RNA (target RNA) is amplified by the continuous-flow RT-PCR chip (52 x 76 mm2) using an FITC labelled and biotinylated primer set. The amplified DNA is mixed with biotin antibodies labelled with gold nanoparticles. The size of the ADLFIA strip is 4 x 40 mm2. FITC antibody and mouse IgG antibody are immobilized on the test and control line, respectively. The mixture is absorbed for ADLFIA, the amplified DNA complex with biotin antibody-labelled gold nanoparticles is captured by the FITC antibody at the test line. Finally, a red color appears as the result of accumulation of gold nanoparticles.
Detection of influenza virus using a lateral flow immunoassay for amplified DNA by a microfluidic RT-PCR chip
Naoki Nagatani, Keiichiro Yamanaka, Hiromi Ushijima, Ritsuko Koketsu, Tadahiro Sasaki, Kazuyoshi Ikuta, Masato Saito, Toshiro Miyahara and Eiichi Tamiya
Analyst, 2012, 137, 3422
(B) Raman images of living HeLa cells, and the same cells were observed after (C) the paraformaldehyde fixation and (D) the H2O2 treatment following the fixation. For each image, Raman intensities at 750, 1686, and 2857 cm-1, which can be assigned to cytochrome c, Amide-I, and CH2 stretching vibration mode, are mapped in green, blue, and red, respectively. Scale bar, 10 μm.
We performed label-free observation ofmolecular dynamics in apoptotic cells by Raman microscopy. Dynamic changes in cytochrome c distribution at the Raman band of 750 cm-1, which is assigned to pyrrole breathing mode ν15 in cytochrome c, were observed after adding an apoptosis inducer to the cells. The comparison of mitochondria fluorescence images and Raman images of cytochrome c confirmed that changes in cytochrome c distribution can be distinguished as release of cytochrome c from mitochondria. Our observation also revealed that the redox state of cytochrome c was maintained during the release from the mitochondria. Monitoring
mitochondrial membrane potential with JC-1 dye confirmed that
the observed cytochrome c release was associated with apoptosis.
PNAS January 3, 2012 vol. 109, p. 28-32.
Label-free Raman observation of cytochrome c dynamics during apoptosis
Masaya Okada, Nicholas Isaac Smith, Almar Flotildes Palonpon,
Hiromi Endo, Satoshi Kawata, Mikiko Sodeoka, and Katsumasa
the 1340 cm−1 image highlights adenine distribution,
189 nm output of CLBO as a function of input fifth-harmonic power.
We report on the phase-matching properties of borate crystals of
LiB3O5 (LBO), CsB3O5 (CBO), and CsLiB6O10 (CLBO) in vacuum–ultraviolet (VUV) light generation at around 190 nm. A new
phase-matching property in the VUV spectral range for CBO grown
from a self-flux solution was found to have better agreement
with new Sellmeier's equations developed in our laboratory. A
189 nm output of 11.4 mW was produced in a CLBO with a conversion efficiency of 7.3% from 213 nm input and the generation efficiency from the source laser was 1.6%. CLBO is suitable for VUV light generation around 190 nm with the present laser system.
Phase-Matching Properties at around 190 nm of Various Borate Crystals
Chen Qu, Masashi Yoshimura, Jun Tsunoda, Kai Zhang, Yushi Kaneda, Mamoru Imade, Takatomo Sasaki, and Yusuke Mori
Appl. Phys. Express 5 (2012) 062601
(a) Schematic of the scattering signals (Rayleigh and Raman) from a Si tip coated with silver, (b) time-dependent lateral displacement of the tip with (solid lines) and without (dotted lines) the scheme of drift compensation and (c) time-dependent change of Raman intensity with and without the compensation scheme. The inset shows a Raman spectrum from the silver-coated Si tip.
We have demonstrated subnanometric stabilization of tip-enhanced optical microscopy under ambient condition. Time-dependent thermal drift of a plasmonic metallic tip was optically sensed at subnanometer scale, and was compensated in real-time. In addition, mechanically induced displacement of the tip, which usually occurs when the amount of tip-applied force varies, was also compensated in situ. The stabilization of tip-enhanced optical microscopy enables us to perform long-time and robust measurement without any degradation of optical signal, resulting in true nanometric optical imaging with high reproducibility and high precision. Even though small-sized samples such as carbon nanotubes and DNA nanocrystals with sizes smaller than 10 nm were positioned under the silver tip, they did not affect the sensitivity and the accuracy of our drift compensation method. This is because scattering efficiency of these samples is much smaller than the metallic tip with the apex size of 40 nm. The technique presented is applicable for AFM-based nanoindentation with subnanometric precision.
Subnanometric stabilization of plasmon-enhanced optical microscopy
Taka-aki Yano, Taro Ichimura, Shota Kuwahara, Prabhat Verma and Satoshi Kawata
Nanotechnology 23 (2012) 205503 (5pp)
TEM images of ZnO–SWNT prepared by ZnO deposition for (a) 3, (b) 7, (c) 15, and (d) 45 min.
(Color online) Photoresponses of ZnO–SWNTs with ZnO layers of various thicknesses and surface morphologies. The theoretical fitting curves are depicted as dashed lines.
Single-walled carbon nanotubes (SWNTs) decorated with zinc oxide (ZnO) nanoparticles show remarkable UV photoresponse and are applicable as UV photodetectors. It is generally accepted that the UV response originates from the adsorption–photodesorption of oxygen from the surface of ZnO nanoparticles. We investigated the UV photoresponse properties of ZnO–decorated SWNTs, which have ZnO layers of various thicknesses and surface morphologies prepared by controlling the pulsed laser deposition (PLD) duration. The magnitude of the negative photocurrent and the recovery time were strongly dependent on the thickness and morphology of the ZnO layer, and were highest when the ZnO layer was 3–4nm thick. We revealed that there are two types of adsorption sites for oxygen on the ZnO layer, which are assigned to the oxygen-vacancy defect site and flat surface site, and that their abundances vary with the thickness and morphology of the ZnO layer, which affect the UV photoresponse properties of ZnO–SWNT devices. The present result suggests that, by controlling the number of defect sites on the ZnO surface, the photoresponse of ZnO–SWNT devices can be improved.
Ultraviolet Photoresponse Properties of Single-Walled Carbon Nanotubes Decorated with Thickness-Controlled ZnO Layer by Pulsed Laser Deposition
Kenta Itabashi, Hiroshi Tabata, Winadda Wongwiriyapan, Shinji Minami, Kazutoshi Matsushita, Ryotaro Shimazaki, Tsuyoshi Ueda, Tatsuya Ito, and Mitsuhiro Katayama
JapaneseJournal of Applied Physics 51 (2012) 055104
Absorption spectrum of Au-capped nanopillars, when they were surrounded by air (n = 1.0), water (n = 1.33), 1 M glucose (n = 1.35), ethylene glycol (n = 1.43), and glycerol (n = 1.47).
Calibration curve for the IgG-anti IgG measurement using Au-capped nanopillar LSPR based-chip. N is 1 μg/mL of CRP as a negative control.
Biosensing with LSPR has the merit of label-free measurement with a highly sensitive signal at long wavelengths. It is widely known that the collective charge density oscillations of nanoparticles are defined as localized surface plasmon resonance. LSPR, in turn, enhances an immediate change in the interfacial refractive index (RI) of the surrounding medium; thus, the signal is greatly afected by the attachment of biomolecules. The excitation of LSPR by light at an incident wavelength, where resonance occurs, results in the appearance of intense surface plasmon (SP) absorption bands. The intensity and position of the SP absorption bands are characteristic to the type of nanomaterial, the diameter of the nanoparticles, and their distribution. Thus, for the development of practical LSPR biosensors, a reliable mass nanofabrication method for noble-metal nanoparticles is one of the key challenges.
In this study, we have developed a novel Au-capped nanopillarplasmonic biosensor based on the combination of porous alumina fabrication and thermal nanoimprinting techniques. A nanoporous alumina was fabricated to use as a mold in transforming nanopillar structures onto a thin film polymer by thermal nanoimprint lithography (NIL). The size of the pores was successfully controlled by varying the applied voltages and etching time. These nanoporous structures were transferred to the Cyclo-olefin polymer (COP) film surface from the porous mold by a thermal nanoimprinting process. A plasmonic substrate was fabricated by sputtering a thin layer of gold onto this nanopillar polymer structure, and the refractive index response in a variety of media was evaluated. Finally, the biosensing capacity of this novel plasmonic substrate was verified by analysis of Human immunoglobulin and achieved a minimum detection limit of 1.0 ng/ mL. With the advantages of mass production with consistent reproducibility stemming from the nanoimprint fabrication process, our gold-capped polymeric pillars are ready for the transition from academic interest into commercialization systems for practical use in diagnostic applications.
Novel Gold-Capped Nanopillars Imprinted on a Polymer Film for Highly Sensitive Plasmonic Biosensing
Masato Saito, Akito Kitamura, Mizuho Murahashi, Keiichiro Yamanaka, Le Quynh Hoa, Yoshinori Yamaguchi, and Eiichi Tamiya
Anal. Chem., 2012, 84 (13), pp 5494-5500
(a) SEM image of a tip fabricated by photoreduction, which we utilized for TERS measurements. (b) Zoomed SEM image of (a). (c) TERS spectra of CNTs taken using the fabricated tip. Inset shows TERS spectra taken using a standard tip that was fully coated with silver. (d) Illustration of experimental conﬁguration for TERS measurement with scanning on two aligned CNTs. (e) TERS intensity at G-band with respect to the tip position for a one-dimensional tip scanning shown in (d). (f) FDTD simulation of ﬁeld distribution in the vicinity of a model tip having a similar shape as the actual tip shown in (b). (g) Line proﬁle of ﬁeld intensity near the tip apex along the white line shown in (f).
Tip-enhanced Raman spectroscopy (TERS) offers one of the best techniques for optical analysis and imaging of samples at nanoscale. The most important point in TERS experiments is to obtain a high signal enhancement through a metallic nanotip.
We present photoreduction as a facile fabrication method for growing near-ﬁeld tips having only one silver nanoparticle at the tip apex. Our technique that selectively grows a silver nanoparticle at the tip apex involves just a simple laser radiation without any requirement of complicated techniques and experimental systems, and the entire fabrication process can be completed in a very short time (a few minutes). It is very easy to control the size of the fabricated silver nanoparticle to meet the TERS experimental requirements.
These tips grown by our method provide an order of magnitude higher enhancement in comparison with the fully metallized standard tips. Our technique of growing tips with a silver nanoparticle has a possibility of improving TERS to a level where it could be a more practical and powerful nanospectroscopic tool due to the better enhancement of the weak Raman signal.Fabrication of Near-Field Plasmonic Tip by Photoreduction for Strong Enhancement in Tip-Enhanced Raman Spectroscopy
Takayuki Umakoshi, Taka-aki Yano, Yuika Saito, and Prabhat Verma
Appl. Phys. Express 5 (2012) 052001
(a) Assumed Kretschmann configuration for calculating plasmon modes at k|| = K/2. Calculated absorptance in terms of the energy, E, versus the relative cylinder radius, r/Λ, for (b)(c) positive plasmonic crystals and (d)(e) negative ones, for (b)(d) p-polarized incidence and (c)(e) s-polarized incidence.
We have investigated the optical properties of two-dimensional plasmonic crystals with triangular lattice structures composed of cylindrical pillars and air holes using rigorous coupled-wave analysis. We revealed the complex band behavior and the radiation properties, which depend on the relative cylinder-radius with respect to the grating pitch, especially around the Γ point. There are always three apparent modes, some of which are degenerate at the Γ point. The number of apparent modes at the Γ point is different from that in photonic crystal slabs with the same lattice structure, which exhibit four apparent modes at that point. All three apparent modes couple to p-polarized radiation, whereas only two of the three apparent modes couple to s-polarized radiation. We also revealed the effect of the shape of the cylinders that compose the lattice of the plasmonic crystals. Deviation of the cylinder cross-section from a perfect circle makes the dispersion relation more complicated and reduces the mode density.
Dispersion relation and radiation properties of plasmonic crystals with triangular lattices
Takayuki Okamoto (RIKEN) and Satoshi KawataOptics Express, Vol. 20, Issue 5, pp. 5168-5177 (2012)
The selective excitation of LRSPs. (a, b) The experimentally observed scattering from the tip (shown by the dashed circle) for the case of Δϕ = 0 (a) and Δϕ = π (b). (c, d) The field distributions (|E|2, on the Ag surface) of SPP modes excited by two beams with Δϕ = 0 (c) and Δϕ = π (d), in the FDTD simulation. The color scale is the same for both figures.
It was demonstrated experimentally that the excitation of long-range surface plasmon polaritons (LRSPs) can be controlled by two incident beams. We have shown the LRSPs modulated by the phase difference or the intensity ratio between the two beams. These results indicate that the excitation control can be applied to active plasmonic devices including modulators, switching and logic gates based on LRSPs. We expect that our findings will further highlight the wide photonic functionality made available by SPPs.
Excitation Control of Long-Range Surface Plasmons by Two Incident Beams
Masashi Miyata and Junichi Takahara
9493 APRIL 2012 VOL 20 OPTICS EXPRESS
Schematic diagrams of micro phase separation in the P3HT:C6PcH2:PCBM active layers, the composition ratios of which are (b) 10:0:10 and (c) 10:3:10.
C6PcH2 transfers electrons and holes through the columnar structures.
We reported on the improvement of the long-wavelength sensitivity in P3HT(poly(3-hexylthiophene)):PCBM (1-(3-methoxy-carbonyl)-propyl-1-1-phenyl-(6,6)C61) bulk heterojunction organic thin-film solar cells by the doping of C6PcH2 (1,4,8,11,15,18,22,25-octahexylphthalocyanine), which is a soluble phthalocyanine derivative exhibiting near-infrared absorption, into the P3HT:PCBM bulk heterojunction active layer. At the composition ratio of P3HT:C6PcH2:PCBM = 10:3:10, the photosensitivity in the wavelength region from 650 to 800 nm was improved, and the short-circuit current density Isc was enhanced from 8.6 to 12.1 mA/cm2. As a result, the energy conversion efficiency was improved from 2.3% to 3.0%. It was found that the bulk heterojunction was composed of both highly ordered P3HT domains and hexagonal columnar structures of C6PcH2 at the P3HT:C6PcH2 composition ratio of 10:3 and that P3HT and C6PcH2 underwent mutual microphase separation in the active layer. We have discussed the mechanisms of photoconversion in the bulk heterojunction organic thin-film solar cell based on the P3HT:C6PcH2:PCBM active layer.Non-peripheral octahexylphthalocyanine doping effects in bulk heterojunction polymer solar cells
Tetsuro Hori, Tetsuya Masuda, Naoki Fukuoka, Takeshi Hayashi, Yasuo Miyake, Toshiya Kamikado, Hiroyuki Yoshida, Akihiko Fujii, Yo Shimizu, Masanori Ozaki
Organic Electronics Volume 13, Issue 2, February 2012, Pages 335–340
Typical SEM images of the PMMA coated Au nanorods with different laser intensity, (a) 1.7 GW/cm2, (b) 3.1 GW/cm2, (c) 3.7 GW/cm2, (d) 4.5 GW/cm2. The scale bar is 100 nm. (e) The thickness of polymer layers covered on the Au nanorods in parallel (black squire) and perpendicular (red dot) directions on the laser intensity. Inset is the schematic of P∥ and P ⊥
(a) Plasmonic field enhancement pattern and (b) contour lines of field strength of the Au nanorods calculated at the 784 nm wavelength
We investigated the plasmonic resonance enhanced two-photon photopolymerization (PETPP) using the isolated chemical synthesized gold nanorods for fabrication of polymer/metal nanocomposites. The isolated gold nanorods with the plasmonic resonance band around 750 nm covered by photoresist were irradiated by a femtosecond laser with the wavelength of 780 nm. The PETPP trigged by the plasmonic resonance enhancement of gold nanorods was localized only in the distance smaller than 30 nm from the surface of gold nanorods, which matched the distance of plasmonic resonant enhanced field of the gold nanorod. The shapes of obtained polymer/gold nanocomposites were changed from the “dumbbell” to the “ellipsoid” with the increase of laser irradiating intensity used for PETPP: the refractive index around the gold nanorod could be changed with the progress of PETPP as the refractive index of the solidified photoresist would be slightly increased after photopolymerization. This change of refractive index from the plasmonic resonance enhanced polymerization of photoresist might occur from the surface area of gold nanorod with strong field enhancement, and lead the new edge forming between the polymer and the surface of gold nanorod and then change the shape of polymer/gold nanocomposites. This study would provide a potential method for fabricating the plasmonic nanomaterials and nanostructures of polymer/metal nanocomposites, which could be expected to be applied in the emerging fields such as anophotonics, nanobiosensor, nanolithography.Plasmonic resonance enhancement of single gold nanorod in two-photon photopolymerization for fabrication of polymer/metal nanocomposites
Kyoko Masui, Satoru Shoji, Feng Jin, Xuan-Ming Duan and Satoshi Kawata
APPLIED PHYSICS A: Volume 106, Number 4 (2012), 773-778, RAPID COMMUNICATION
Absorption spectra (a) and PL emission spectra (b) of OLA-AIS nanoparticles. The excitation wavelength in PL spectra was 430 nm. The numbers in the figures represent the ratios of NAg/Nmetal in precursors. Photographs of the chloroform solution containing OLA-AIS particles under UV light irradiation are shown in (c).
Non-stoichiometric AgInS2 (AIS) semiconductor particles were synthesized by the thermal decomposition of single-source precursors in solutions of two kinds of primary amines (oleylamine and octylamine). The Ag content in the resulting nanoparticles was controlled by adjusting the chemical composition of the precursor used, in which the mole ratio of Ag+ to total metal ions was varied from 0.1 to 0.7, resulting in the production of non-stoichiometric AIS particles with varying amounts of Ag vacancies. The average size of AIS particles was slightly decreased from 4.3 to 3.8 nm on changing the solvent from oleylamine to octylamine in the preparation, while the particle size seemed to be constant regardless of the content of Ag. On the other hand, the optical properties of AIS particles were considerably modified depending on the Ag content in the particles. The absorption onset was blueshifted from 750 to 580 nm with a decrease in the Ag content, due to the enlargement of the energy gap of particles. Intense photoluminescence originating from the donor-acceptor pair recombination was observed for each kind of AIS particle and then the photoluminescence peak wavelength was also blueshifted from 830 to 650 nm, being similar to the behavior of the absorption onset. The maximum photoluminescence quantum yield was ca. 70% for octylamine-modified AIS nanoparticles having a ratio of Ag+ to total metal ions of 0.37, which probably contained the optimum amount of Ag vacancies acting as the sites of donor-acceptor pair recombination with few surface defect sites for nonradiative recombination.
Tunable photoluminescence from the visible to near-infrared wavelength region of non-stoichiometric AgInS2nanoparticles
Meilin Dai, Shoji Ogawa, Tatsuya Kameyama, Ken-ichi Okazaki, Akihiko Kudo, Susumu Kuwabata, Yasuyuki Tsuboi and Tsukasa Torimoto
J. Mater. Chem., 2012, 22, 12851
Correlation between rate constant in photocatalytic degradation k and hydrophobicity index (HI) of zeolite supports (filled circles: degradation of 2-propanol diluted in water; open circles: degradation of acetaldehyde diluted in air; triangle symbols correspond to the physically mixed sample)
Highly hydrophobic FAU zeolite was prepared by a two-step preparation method and was utilized as a support for TiO2photocatalyst. The photocatalytic degradation rates were significantly improved both in aqueous- and in gaseous phase reactions because of its improved hydrophobic character, which was clearly elucidated on the basis of sorptive analyses and photocatalytic tests. It was also practically demonstrated that the photocatalytic efficiency of zeolite-supported TiO2 is strongly associated with the surface hydrophobicity of zeolite and the corresponding adsorption kinetics of water and organic molecules. We expect that this preparation route will be extendable to the other types of zeolite materials by optimizing the preparation conditions, although the highest hydrophobicity was observed in FAU zeolite. Due to their prominent hydrophobicity, they could advantageously replace conventional molecular sieves, adsorbents, and catalyst supports in the specific applications that require a high affinity with organic molecules. In particular, the combination of a TiO2 photocatalyst with the hydrophobic FAU zeolites is expected to greatly assist photocatalytic degradation reactions involving organic molecules and will expand the application of TiO2photocatalysts for environmental remediation.
TiO2 photocatalyst for degradation of organic compounds in water and air supported on highly hydrophobic FAU zeolite: Structural, sorptive, and photocatalytic studies
Journal of Catalysis 285 (2012) 223-234
Yasutaka Kuwahara, Junya Aoyama, Keisuke Miyakubo, Taro Eguchi, Takashi Kamegawa, Kohsuke Mori, Hiromi Yamashita
Results of hyperspectral imaging of PS beads and PMMA beads. Scale bar, 10 μm. (a)-(d) SRS images of different wavenumbers. (e) SRS spectra of PS and PMMA reconstructed from the SRS images.
When the optical frequency difference of the two-color laser pulses, the one of which with high-frequency is intensity modulated, matches the vibrational frequency of the sample molecules, the optical energy of the high-frequency pulse is transferred to the low-frequency pulse and to molecular vibrations through the stimulated Raman scattering (SRS) process. The intensity modulation transferred to the other pulse is measured by the lock-in detection technique. We have developed a high-resolution tunable bandpass filter (TBPF) that can be controlled quickly by a galvanometer mirror and applied it to spectral filtering of broadband Yb fiber laser pulses. After optical amplification, we succeeded in obtaining narrowband pulses with a tunability of >225 cm-1 and a spectral width of <3.3 cm-1. These pulses were used along with picosecond Ti:sapphire pulses to demonstrate hyperspectral imaging of polymer beads in SRS microscopy. The present approach is advantageous in terms of the high tuning speed and the high spectral resolution, and will be useful for high-speed hyperspectral SRS imaging. The wavelength tunability may be extended up to 500 cm-1 by further optimization. Moreover, the use of multiple-wavelength pump pulses, which can be generated by fiber-based laser sources, would enable us to acquire SRS signals in different vibrational regions simultaneously.
6.Optics Letters, Vol. 37, Issue 3, pp. 431-433 (2012)
Stimulated Raman hyperspectral imaging based on spectral filtering of broadband fiber laser pulses
Yasuyuki Ozeki, Wataru Umemura, Kazuhiko Sumimura, Norihiko Nishizawa, Kiichi Fukui, and Kazuyoshi Itoh
A no-wash fluorogenic labeling system by exploiting fluorescence resonance energy transfer (FRET)-based fluorescein-cephalosporin-azopyridinium probes and a mutant β-lactamase tag. Fast quencher elimination, hydrophilicity, and high resistance against autodegradation were achieved by rational refinement of the structure. By applying the probe to real-time pulse-chase analysis, the trafficking of epidermal growth factor receptors between cell surface and intracellular region was imaged. In addition, membrane-permeable derivatization of the probe enabled no-wash fluorogenic labeling of intracellular proteins.
No-wash protein labeling with designed fluorogenic probes and application to real-time pulse-chase analysis
Mizukami S, Watanabe S, Akimoto Y, Kikuchi K.J Am Chem Soc. 2012 Jan 25;134(3):1623-9. Epub 2012 Jan 6.