Browsing by Author "Uwada, Takayuki"

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Assembling and crystallization of amino acids and proteins by intense laser irradiation in solution
(2011-08-28)
Masuhara, Hiroshi
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Sugiyama, Teruki
;
Yuyama, Ken-ichi
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Uwada, Takayuki
;
Miura, Atsushi
Fabrication of gold nanoparticle-doped zeolite L crystals and characterization by optical microscopy: Laser ablation- and crystallization inclusion-based approach
(2008-10-02)
Hashimoto, Shuichi
;
Uwada, Takayuki
;
Masuhara, Hiroshi
;
Asahi, Tsuyoshi
;
應用化學系
This letter reports the optical microscopy characterization of gold nanoparticle-doped zeolite L crystals prepared by applying two key techniques: laser ablation and crystallization inclusion. The former allowed the stable formation of Au NPs in the synthesis gel, while the latter permitted the encapsulation of Au NPs exceeding the pore openings of the zeolite crystals, still maintaining the crystal structure as a whole. The microscopy characterization was performed by exploiting single particle light scattering spectroscopy and imaging techniques which offered the Rayleigh scattering images of individual An particles within the crystals and the scattering spectra ascribable to the surface plasmon resonance band of Au NPs embedded. This is a unique demonstration for the application of laser ablation-induced NPs in solution to practical use for fabricating a nanocomposite material. Furthermore, the present results revealed that the dark field microscopy is capable of visualizing metal nanoparticles as small as 40 nm diameter confined in the light scattering crystalline medium.
Glycine Crystallization in Solution by CW Laser-Induced Microbubble on Gold Thin Film Surface
(2012-03-01)
Uwada, Takayuki
;
Fujii, Sho
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Sugiyama, Teruki
;
Usman, Anwar
;
Miura, Atsushi
We have developed a novel laser-induced crystallization method utilizing local heat-induced bubble/water interface. Continuous laser beam of 1064 nm is focused on a gold nanoparticles thin film surface covered with glycine supersaturated aqueous solution. Light absorption of the film due to localized plasmon resonance caused local heating at the focal position and produced a single thermal vapor microbubble, which generated thermal gradient followed by convection flow around the bubble and eventually induced glycine crystallization and growth. The crystallization mechanism is discussed by considering gathering and accumulating molecules around the bubble/water interface assisted by convection flow and temperature jump.
Gold Nanoparticle-Assisted Laser Surface Modification of Borosilicate Glass Substrates
(2009-12-03)
Hashimoto, Shuichi
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Uwada, Takayuki
;
Hagiri, Masahide
;
Takai, Hiroaki
;
Ueki, Tomoyuki
This paper describes the photomodification of borosilicate glass substrates assembled with 40 nm diameter gold nanoparticles (Au NPs) with surface coverages ranging from 17 to 23% on excitation of the localized surface plasmon band of the NPs with a 532 nm nanosecond pulsed-laser beam. The laser irradiation allowed the splitting and fusion of NPs on the substrate surface and, at the same time, the formation of craters of less than 10 nm diameter at various places following one laser shot with a relatively high intensity of 460 or 370 mJ.cm(-2).pulse(-1) but well below the breakdown threshold of 25-40 J.cm(-2).pulse(-1). The formation of the craters was more and more distinctly observed by continuous irradiations. The number density, average diameter, and the surface coverage of the craters were not linearly dependent on the laser shot number but exhibited the saturation behavior due to the consumption of Au NPs. The threshold laser energy for the crater formation was dependent on the accumulated number of laser shots: a greater number of laser shots were necessary to form craters as the laser fluence decreases. Most interestingly, the laser-irradiated areas of the substrate exhibited a greater susceptibility to the wet chemical etching with aqueous hydrogen fluoride. The mechanism of the laser modification and a possible application to nanofabrication on glass surfaces by utilizing Au NPs were discussed on the basis of the scanning electron microscopy (SEM) observation as well as the extinction and light scattering spectroscopic measurements.
Laser Trapping-Induced Reconfiguration of Individual Smectic Liquid Crystal Micro-Droplet Showing Size-Dependent Dynamics
(2012)
Usman, Anwar
;
Chiang, Wei-Yi
;
Uwada, Takayuki
;
Masuhara, Hiroshi
;
應用化學系
We present laser trapping behavior of individual smectic 4'-n-pentyl-4-cyanobiphenyl liquid crystalline micro-droplet dispersed in heavy water; in particular, laser trapping-induced molecular reconfiguration of the optically trapped droplet when the laser trapping power is above a definite threshold. The reconfiguration undergoes throughout the inside of the droplets even though their size is larger than the focal spot, and the threshold laser power depends on the droplet size. We propose that the reconfiguration mechanism involves optical reorientation at the focal volume competing with the droplet-liquid interfacial anchoring effect, leading to symmetry breaking throughout the inside of the optically confined droplet. With this mechanism, we qualitatively described the existence of the threshold power and the dependence of the threshold upon the droplet size.
Mechanistic Aspect of Surface Modification on Glass Substrates Assisted by Single Shot Pulsed Laser-Induced Fragmentation of Gold Nanoparticles
(2011-03-31)
Hashimoto, Shuichi
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Uwada, Takayuki
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Hagiri, Masahide
;
Shiraishi, Ryowya
;
應用化學系
This paper describes the mechanistic investigation on the photomodification of a borosilicate glass substrate assembled with 47 +/- 8 nm gold nanoparticles and exposed to a single shot of 532 nm nanosecond pulsed-laser light. The laser fluences ranging from 180 to 430 mJ cm(-2) pulse(-1), the values of which are 2 orders of magnitude lower than the breakdown threshold of quartz of 15-20 J cm(-2) pulse(-1) were used. Upon photomodification, the craters of similar to 20 nm diameter and similar to 10 tun depth were formed on the glass surface simultaneously with the laser-induced splitting of Au nanopartides to generate smaller particles of 15 nm diameter. The number density of the craters increased depending on the laser fluence with a sharp rise, the onset of which occurred at similar to 160-170 mJ cm(-2) pulse(-1), and reached a value of twice the number density of original Au particles (150 +/- 10 particles mu m(-2)) with a weak tendency to level off at high fluences. The onset of the crater formation coincides with splitting of gold nanopartides due to the temperature rise above the boiling point of gold resulting from the absorption of the laser energy. Thus, the explosive evaporation of gold nanoparticles is postulated to play a crucial role for the modification observed here. This assumption gained a solid support from the estimation of laser fluence-dependent thermoacoustic pressures due to the sudden evaporation of gold. This finding may represent a new application of the laser ablation/fragmentation of nanoparticles to material processing.
Optical Reorientation and Trapping of Nematic Liquid Crystals Leading to the Formation of Micrometer-Sized Domain
(2011-06-23)
Usman, Anwar
;
Uwada, Takayuki
;
Masuhara, Hiroshi
;
應用化學系
;
應用化學系分子科學碩博班
We report on observation of optical reorientation of homogeneous nematic liquid crystals (LCs) thin slab of 4'-penthyl-4-cyanobiphenyl induced by a tightly focused nearinfrared laser beam. We found that for laser beam with intensity higher than 56 MW/cm(2) the optical reorientation unusually transforms to a new metastable domain, which grows with laser irradiation time up to a dimension much larger than that of the focal spot. The optically reoriented LCs with refractive index mismatch compared to the surroundings can act as a micrometer-sized "ghost particle", leading to the generation of optical trapping and manipulation of the optically reoriented LCs. By using confocal Raman microspectroscopy, we show that the dichroic ratio in the confined focal volume changes upon the domain formation with an increase in the total Raman intensity, indicating that microscopic depolarization leading to deorientation or nematic isotropic phase transition and possible microscopic densification takes place by the tightly focused laser beam.
Polarization and Droplet Size Effects in the Laser-Trapping-Induced Reconfiguration in Individual Nematic Liquid Crystal Microdroplets
(2013-04-25)
Usman, Anwar
;
Chiang, Wei-Yi
;
Uwada, Takayuki
;
Masuhara, Hiroshi
;
應用化學系
We experimentally demonstrate reordering throughout the inside of an individual bipolar nematic liquid-crystalline microdroplet optically trapped by a highly focused laser beam, when the laser powers are above a definite threshold. The threshold depends on the droplet size and laser polarization. A physical interpretation of the results is presented by considering the nonlocal orientations of the nematic liquid-crystal molecules in the droplets with the dimensions on the order of the focal spot diameter or larger. On the basis of the finite size approximation, we show that the dependence of threshold power on the droplet size is calculated to be in qualitative agreement with the experimental data.
Preparation and micropatterning of gold nanoparticles by femtosecond laser-induced optical breakdown
(2017-09-01)
Uwada, Takayuki
;
Wang, Shun-Fa
;
Liu, Tsung-Han
;
Masuhara, Hiroshi
;
應用化學系
We fabricated gold nanoparticles (NPs) via a femtosecond (fs) laser-induced cavitation bubbling. By introducing intense fs laser pulses into HAuCI4 aqueous solution containing 1-propanol, optical breakdown and the following cavitation bubble generation occurred at the focus through multiphoton absorption of water, resulting in the formation of gold nanoparticles (Au NPs). Intermediate species such as radicals and solvated electrons produced upon the bubbling contribute to gold ion reduction, while direct ionization of Au-chloride complex, photothermal decomposition and direct optical decomposition are excluded as possible mechanisms. Utilizing the fs laser-induced bubbling we demonstrate in-situ micropatterning of Au NPs on a substrate from the same HAuCI4 aqueous solution containing 1-propanol. (C) 2017 Elsevier B.V. All rights reserved.
Rayleigh scattering correlation spectroscopy on diffusion dynamics of nanoparticles under intense laser irradiation
(2013)
Hee, Ping-Yu
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Uwada, Takayuki
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Okano, Kazunori
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Miura, Atsushi
;
Masuhara, Hiroshi
Rayleigh scattering correlation microspectroscopy is developed and applied to study diffusion dynamics of some nanospheres in water. It was clearly found that the diffusion constant of gold nanoparticles decreased with increasing excitation laser power at the excitation wavelength of higher absorption cross section. This behavior was explained in terms of a coupling between laser trapping by the scattering excitation laser itself and laser heating of the particle. In the case of non-absorbing nanospheres such as silica and polystyrene, the excitation power dependence can be ascribed only to the laser trapping. Experimental setup is introduced, theoretical formulation is described, and future development of this measurement is considered.
Remarkable Photothermal Effect of Interband Excitation on Nanosecond Laser-Induced Reshaping and Size Reduction of Pseudospherical Gold Nanoparticles in Aqueous Solution
(2010-06-15)
Werner, Daniel
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Hashimoto, Shuichi
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Uwada, Takayuki
;
應用化學系
;
應用化學系分子科學碩博班
An in situ spectroscopic study of the nanosecond laser-induced melting and size reduction of pseudospherical gold nanoparticles with 54 +/- 7 nm diameter allowed the observation of a heating efficiency that was very dependent on the excitation wavelength. A remarkably greater efficiency was observed for the photothermal effect of interband excitation than that of intraband excitation. This noteworthy observation is ascribed to an altered electron heat capacity, c(e), during photoexcitation depending on the excitation energy, which is a phenomenon that has not been realized previously. As a result, a 60% reduction of the specific heat capacity, c(p), compared to that of bulk gold was obtained for interband excitation at 266 nm whereas the c(p) value for the excitation of the intraband transition at 532 nm was unaltered. A semiquantitative explanation was given for this striking phenomenon induced by interband excitation in which excitation relaxation cycles of electrons upon excitation of 5d electrons to the 6sp band lead to a reduced number of electrons contributing to the electron temperature rise in the vicinity of the Fermi level during the nanosecond laser pulse duration. By contrast, electronic-excitation within the 6sp band results in no net reduction in the number of electrons near the Fermi level, giving rise to a value of c(p) similar to that of bulk gold. Our finding that the heat capacity of gold nanoparticles can be changed upon UV laser excitation is important for understanding the fundamental nature of noble metal nanoparticles. Furthermore, this finding might be useful for preparing new metal alloy particles as well as for manipulating the thermodynamic properties of the nanoparticles.
Single femtosecond laser pulse-single crystal formation of glycine at the solution surface
(2013-03-01)
Liu, Tsung-Han
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Uwada, Takayuki
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Sugiyama, Teruki
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Usman, Anwar
;
Hosokawa, Yoichiroh
We demonstrate femtosecond laser-induced crystallization of glycine from its supersaturated solution depending on laser tunable parameters (pulse energy and repetition rate) and focal position, and examine the crystallization probability, crystal morphology, and crystal polymorph. The generation of cavitation bubble through multiphoton absorption of water depends on input laser pulse energy and repetition rate, which strongly determine morphology and number of the obtained crystals. Significant increase in the crystallization probability is observed by irradiating the femtosecond laser pulses to the air/solution interface, and single pulse-induced single crystal formation is successfully achieved. The crystallization mechanism is discussed in view of inhomogeneous mechanical stress induced by cavitation bubble generation and molecular assembly characteristics of the surface. (C) 2012 Elsevier B.V. All rights reserved.
Single particle spectroscopy and tracking of gold nanospheres in living cells by conforcal light scattering microsopy
(2008)
Asahi, Tsuyoshi
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Uwada, Takayuki
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Louit, Guillaume
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Masuhara, Hiroshi
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應用化學系
Size-Dependent Optical Properties of Grana Inside Chloroplast of Plant Cells
(2017-02-09)
Uwada, Takayuki
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Huang, Ling-Ting
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Hee, Ping-Yu
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Usman, Anwar
;
Masuhara, Hiroshi
Well-packed thylakoids known as grana are one of the major functional sites for photosynthesis in algae and plants. Their highly ordered structures can be considered as a few hundred nanometer-sized particles having distinct scattering cross sections from other various macromolecular organizations inside plant cells. With this background we shOw that elastic light scattering imaging and microspectroscopy is an important tool for investigating structure and organisation of grana inside a single chloroplast in plant tells. We have demonstrated this noninvasive method to identify the distribution of grana in intact fresh leaf of robust and rapidly growing Egaria densa, which is also known as Anachris and among the most popular aquarium plants. The scattering efficiency spectra of their individual grana fairly resemble cooperative absorption spectra of porphyrins and carotenoids. We found that the electronic structure of the stacked thylakoids shows granum size-dependence, indicating that size of grana is one of the critical parameters in the regulation of the photochemical functions in the thylakoid.
Spectral and 3-Dimensional Tracking of Single Gold Nanoparticles in Living Cells Studied by Rayleigh Light Scattering Microscopy
(2009-07-09)
Louit, Guillaume
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Asahi, Tsuyoshi
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Tanaka, Go
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Uwada, Takayuki
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Masuhara, Hiroshi
Using a confocal Rayleigh light scattering microspectroscopy and imaging system, we followed and recorded the scattering spectra of single gold nanoparticles interacting with living mouse fibroblast cells, during the scale of I h. A white light continuum produced by a femtosecond laser was focused on gold nanoparticles with a diameter of 80 nm, while an incubation system ensured viability of the living cells. After reporting spectral characteristics of gold nanoparticles and their target fibroblasts, separately and in combination, tracking sequences of single nanoparticles in contact with a single cell are described. Through the study of three separate and representative cases, transitory as well as plasmon resonance band shifts, which can be linked to biological events, have been observed and are discussed here.
Studies on the interaction of pulsed lasers with plasmonic gold nanoparticles toward light manipulation, heat management, and nanofabrication
(2012-03-01)
Hashimoto, Shuichi
;
Werner, Daniel
;
Uwada, Takayuki
;
應用化學系
;
應用化學系分子科學碩博班
This review describes the fundamental aspects of laser-gold nanoparticle (Au NP) interaction that leads to nanoscale energy deposition to the surroundings through light amplification and heat generation. Besides the importance of the primary process in physics and chemistry, application of the light-NP interaction has attracted significant interest from various areas ranging from analytical chemistry to material chemistry and biomedicine. Here we consider both mechanistic and application aspects. Our attention is focused on pulsed-laser-induced fast processes that revealed the heating-cooling dynamics of electrons, lattice (particle), and particle's environment. On the application side, we focus on material fabrication and processing that beat diffraction-limited resolution. Together, we will shed a light on the essence of research activities carried out in the past 10 years. In addition to an abundance of latest information obtained from currently available literature, this review includes figures obtained by our own calculations to provide readers with a better understanding of the basics of the optical properties and energy and heat-transfer processes of Au NPs, which are not familiar to photochemists. (C) 2012 Elsevier B.V. All rights reserved.
Wide-field light scattering imaging of laser trapping dynamics of single gold nanoparticles in solution
(2010)
Uwada, Takayuki
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Sugiyama, Teruki
;
Miura, Atsushi
;
Masuhara, Hiroshi
;
應用化學系
We present direct observation of particle transfer and assembling upon laser irradiation under a microscope. We employed gold nanoparticles (60 nm) dispersed in water as optical markers and studied laser trapping and accompanying phenomenon by wide-field Rayleigh scattering microscopy. At the focal spot of the near IR laser, laser trapping of gold was observed. Simultaneously, we observed that the particle migration toward the focal spot from all the directions within several tens micrometer. We consider that thermocapillary effect due to laser heating can assist the particle migration from far away, resulting in concentration increase not only at the focal point but also near the surrounding area.
Wide-field Rayleigh scattering imaging and spectroscopy of gold nanoparticles in heavy water under laser trapping
(2011-06-25)
Uwada, Takayuki
;
Sugiyama, Teruki
;
Masuhara, Hiroshi
;
應用化學系
;
應用化學系分子科學碩博班
We demonstrated wide-field Rayleigh scattering spectroscopy and imaging of gold nanoparticle trapping upon a focused near-infrared laser irradiation under dark-field illumination. The migration, trapping, and assembling behavior of gold nanoparticles were examined at single nanoparticle level at the focus spot and its surrounding area in heavy water. It is clarified that particle migration to the laser spot within the focal plane is not appreciable while scattering force drives the migration vertically along the direction of light propagation. The gradient force at the focus point and the scattering force are theoretically estimated to be 3.1 and 0.17 pN, which are consistent with the direct observation. Analysis of light scattering intensity fluctuation at the focus shows that three nanoparticles can be trapped at most, which is well supported by light scattering spectral measurement. The particle existence probability at the focus is estimated as a function of lateral distance from the focus, and is compared with numerically obtained photon pressure potential. (C) 2011 Elsevier B.V. All rights reserved.